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PROGRAMMING IN JAVA
A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION
10
Software objects also have a state and a behavior. A software object's state is stored
in fields and behavior is shown via methods.
So in software development, methods operate on the internal state of an object and the
object-to-object communication is done via methods.
First Java Program | Hello World Example
1. Software Requirements
2. Creating Hello Java Example
3. Resolving javac is not recognized
To create a simple java program, you need to create a class that contains the main
method. Let's understand the requirement first.
The requirement for Java , Welcome To Java Example
For executing any java program, you need to
o Install the JDK if you don't have installed it, download the JDK and install it.
o Set path of the jdk/bin directory. http://www.javatpoint.com/how-to-set-path-in-java
o Create the java program
o Compile and run the java program
SYNTAX OF CLASS:
Class classname
{
Type instance variable 1;
.
.
.
Type instance variable N;
Type methodname1(parameter list)
{
Body of the method
}
Type methodnameN(parameter list)
{
Body of the method
}
}
Simple Program:
Class Simple
{
public static void main(String args[])](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-10-320.jpg)
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12
TWO TYPES
Syntax of Object
1. Classname objectname=new classname()
2. Classname objectname;
Objectname=new classname();
Example of Object Declaration
1. Box mybox=new Box());
2. Box mybox;
mybox=new box();
SAMPLE PROGRAM:
Class box
{
Double width;
Double height;
Double depth;
}
Class boxdemo
{
public static void main(String args[])
box mybox=new box();
Double volume;
Mybox.width=10;
Mybox.height=20;
Mybox.depth=15;
Volume=mybox.width*mybox.height*mybox.depth;
System.out.println(“The value is :”+ volume);
}
}
JAVA - BASIC DATATYPES
Variables are nothing but reserved memory locations to store values. This means that
when you create a variable you reserve some space in the memory.
Based on the data type of a variable, the operating system allocates memory and decides
what can be stored in the reserved memory. Therefore, by assigning different data types to
variables, you can store integers, decimals, or characters in these variables.
There are two data types available in Java −
• Primitive Data Types
• Reference/Object Data Types
Primitive Data Types](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-12-320.jpg)
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String literals in Java are specified like they are in most other languages by enclosing a
sequence of characters between a pair of double quotes. Examples of string literals are −
Example
"Hello World"
"twonlines"
""This is in quotes""
String and char types of literals can contain any Unicode characters. For example −
char a = 'u0001';
String a = "u0001";
VARIABLE TYPES
A variable provides us with named storage that our programs can manipulate. Each
variable in Java has a specific type, which determines the size and layout of the variable's
memory; the range of values that can be stored within that memory; and the set of operations
that can be applied to the variable.
You must declare all variables before they can be used. Following is the basic form
of a variable declaration −
data type variable [ = value][, variable [ = value] ...] ;
Here data type is one of Java's datatypes and variable is the name of the variable. To
declare more than one variable of the specified type, you can use a comma-separated list.
Following are valid examples of variable declaration and initialization in Java −
Example
int a, b, c; // Declares three ints, a, b, and c.
int a = 10, b = 10; // Example of initialization
byte B = 22; // initializes a byte type variable B.
double pi = 3.14159; // declares and assigns a value of PI.
char a = 'a'; // the char variable a iis initialized with value 'a'
This chapter will explain various variable types available in Java Language. There are three
kinds of variables in Java −
• Local variables
• Instance variables
• Class/Static variables
Local Variables
• Local variables are declared in methods, constructors, or blocks.
• Local variables are created when the method, constructor or block is entered and the
variable will be destroyed once it exits the method, constructor, or block.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-16-320.jpg)
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• Access modifiers cannot be used for local variables.
• Local variables are visible only within the declared method, constructor, or block.
• Local variables are implemented at stack level internally.
• There is no default value for local variables, so local variables should be declared and
an initial value should be assigned before the first use.
Example
Here, age is a local variable. This is defined inside pupAge() method and its scope is limited
to only this method.
public class Test {
public void pupAge() {
int age = 0;
age = age + 7;
System.out.println("Puppy age is : " + age);
}
public static void main(String args[]) {
Test test = new Test();
test.pupAge();
}
}
This will produce the following result
Output
Puppy age is: 7
Instance Variables
• Instance variables are declared in a class, but outside a method, constructor or any
block.
• When a space is allocated for an object in the heap, a slot for each instance variable
value is created.
• Instance variables are created when an object is created with the use of the keyword
'new' and destroyed when the object is destroyed.
• Instance variables hold values that must be referenced by more than one method,
constructor or block, or essential parts of an object's state that must be present
throughout the class.
• Instance variables can be declared in class level before or after use.
• Access modifiers can be given for instance variables.
• The instance variables are visible for all methods, constructors and block in the class.
Normally, it is recommended to make these variables private (access level).](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-17-320.jpg)
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However, visibility for subclasses can be given for these variables with the use of
access modifiers.
• Instance variables have default values. For numbers, the default value is 0, for
Booleans it is false, and for object references it is null. Values can be assigned during
the declaration or within the constructor.
Instance variables can be accessed directly by calling the variable name inside the class.
However, within static methods (when instance variables are given accessibility), they should
be called using the fully qualified name. ObjectReference.VariableName
import java.io.*;
public class Employee {
// this instance variable is visible for any child class.
public String name;
// salary variable is visible in Employee class only.
private double salary;
// The name variable is assigned in the constructor.
public Employee (String empName) {
name = empName;
}
// The salary variable is assigned a value.
public void setSalary(double empSal) {
salary = empSal;
}
// This method prints the employee details.
public void printEmp() {
System.out.println("name : " + name );
System.out.println("salary :" + salary);
}
public static void main(String args[]) {
Employee empOne = new Employee("Ransika");
empOne.setSalary(1000);
empOne.printEmp();
}
}
Output
name : Ransika
salary :1000.0
Class/Static Variables](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-18-320.jpg)
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• Class variables also known as static variables are declared with the static keyword in
a class, but outside a method, constructor or a block.
• There would only be one copy of each class variable per class, regardless of how
many objects are created from it.
• Static variables are rarely used other than being declared as constants. Constants are
variables that are declared as public/private, final, and static. Constant variables
never change from their initial value.
• Static variables are stored in the static memory. It is rare to use static variables other
than declared final and used as either public or private constants.
• Static variables are created when the program starts and destroyed when the program
stops.
• Visibility is similar to instance variables. However, most static variables are declared
public since they must be available for users of the class.
• Default values are same as instance variables. For numbers, the default value is 0; for
Booleans, it is false; and for object references, it is null. Values can be assigned
during the declaration or within the constructor. Additionally, values can be assigned
in special static initializer blocks.
• Static variables can be accessed by calling with the class
name ClassName.VariableName.
• When declaring class variables as public static final, then variable names (constants)
are all in upper case. If the static variables are not public and final, the naming
syntax is the same as instance and local variables.
import java.io.*;
public class Employee {
// salary variable is a private static variable
private static double salary;
// DEPARTMENT is a constant
public static final String DEPARTMENT = "Development ";
public static void main(String args[]) {
salary = 1000;
System.out.println(DEPARTMENT + "average salary:" + salary);
}](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-19-320.jpg)
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}
Output
Development average salary:1000
MODIFIER TYPES
Modifiers are keywords that you add to those definitions to change their meanings. Java
language has a wide variety of modifiers, including the following −
• Java Access Modifiers
• Non Access Modifiers
To use a modifier, you include its keyword in the definition of a class, method, or variable.
The modifier precedes the rest of the statement, as in the following example.
Example
public class className {
// ...
}
private boolean myFlag;
static final double weeks = 9.5;
protected static final int BOXWIDTH = 42;
public static void main(String[] arguments) {
// body of method
}
Access Control Modifiers
Java provides a number of access modifiers to set access levels for classes, variables,
methods and constructors. The four access levels are −
• Visible to the package, the default. No modifiers are needed.
• Visible to the class only (private).
• Visible to the world (public).
• Visible to the package and all subclasses (protected).
Non-Access Modifiers
Java provides a number of non-access modifiers to achieve many other functionality.
• The static modifier for creating class methods and variables.
• The final modifier for finalizing the implementations of classes, methods, and
variables.
• The abstract modifier for creating abstract classes and methods.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-20-320.jpg)
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• The synchronized and volatile modifiers, which are used for threads.
DYNAMIC INITIALIZATION:
Class sample
{
Public static void main(String args[])
{
int a=,b=4; //dynamic intialization
int c=math.sqrt(a*a + b*b);
System.out.println(“The value of c is “+c);
}
}
Output:
The value of c is: 5
TYPE CONVERSION AND CASTING:
One data type automatically converted into another.
Example:
int a,b;
float c;
c=a+b;
ARRAY AND ITS TYPES
Group of elements and group of array is called array.
▪ One dimensional
▪ Two dimensional
▪ Multi dimensional
Java provides a data structure, the array, which stores a fixed-size sequential
collection of elements of the same type. An array is used to store a collection of data, but it
is often more useful to think of an array as a collection of variables of the same type.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-21-320.jpg)
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Instead of declaring individual variables, such as number0, number1, ..., and number99, you
declare one array variable such as numbers and use numbers[0], numbers[1], and ...,
numbers[99] to represent individual variables.
Declaring Array Variables
To use an array in a program, you must declare a variable to reference the array, and
you must specify the type of array the variable can reference. Here is the syntax for
declaring an array variable −
Syntax
dataType[] arrayRefVar; // preferred way.
or
dataType arrayRefVar[]; // works but not preferred way.
Note − The style dataType[] arrayRefVar is preferred. The style dataType
arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate
C/C++ programmers.
Example
The following code snippets are examples of this syntax −
double[] myList; // preferred way.
or
double myList[]; // works but not preferred way.
Creating Arrays
You can create an array by using the new operator with the following syntax −
Syntax
arrayRefVar = new dataType[arraySize];
The above statement does two things −
• It creates an array using new dataType[arraySize].
• It assigns the reference of the newly created array to the variable arrayRefVar.
Declaring an array variable, creating an array, and assigning the reference of the array to the
variable can be combined in one statement, as shown below −
dataType[] arrayRefVar = new dataType[arraySize];
Alternatively you can create arrays as follows −
dataType[] arrayRefVar = {value0, value1, ..., valuek};
The array elements are accessed through the index. Array indices are 0-based; that is,
they start from 0 to arrayRefVar.length-1.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-22-320.jpg)
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Example
Following statement declares an array variable, myList, creates an array of 10 elements of
double type and assigns its reference to myList −
double[] myList = new double[10];
Following picture represents array myList. Here, myList holds ten double values and the
indices are from 0 to 9.
Processing Arrays
When processing array elements, we often use either for loop or foreach loop because all of
the elements in an array are of the same type and the size of the array is known.
public class TestArray {
public static void main(String[] args) {
double[] myList = {1.9, 2.9, 3.4, 3.5};
// Print all the array elements
for (int i = 0; i < myList.length; i++) {
System.out.println(myList[i] + " ");
}
// Summing all elements
double total = 0;
for (int i = 0; i < myList.length; i++) {
total += myList[i];
}
System.out.println("Total is " + total);
// Finding the largest element
double max = myList[0];
for (int i = 1; i < myList.length; i++) {
if (myList[i] > max) max = myList[i];](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-23-320.jpg)
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}
System.out.println("Max is " + max);
}
}
This will produce the following result −
Output
1.9
2.9
3.4
3.5
Total is 11.7
Max is 3.5
Enhanced for loop in Java
As of Java 5, the enhanced for loop was introduced. This is mainly used to traverse
collection of elements including arrays.
Syntax
Following is the syntax of enhanced for loop −
for(declaration : expression) {
// Statements
}
• Declaration − The newly declared block variable, is of a type compatible with the
elements of the array you are accessing. The variable will be available within the for
block and its value would be the same as the current array element.
• Expression − This evaluates to the array you need to loop through. The expression
can be an array variable or method call that returns an array.
Example
public class Test {
public static void main(String args[]) {
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ) {
System.out.print( x );
System.out.print(",");
}
System.out.print("n");
String [] names = {"James", "Larry", "Tom", "Lacy"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-24-320.jpg)
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STRINGS CLASS
Strings, which are widely used in Java programming, are a sequence of characters. In
Java programming language, strings are treated as objects.
The Java platform provides the String class to create and manipulate strings.
Creating Strings
The most direct way to create a string is to write −
String greeting = "Hello world!";
Whenever it encounters a string literal in your code, the compiler creates a String object
with its value in this case, "Hello world!'.
As with any other object, you can create String objects by using the new keyword and a
constructor. The String class has 11 constructors that allow you to provide the initial value
of the string using different sources, such as an array of characters.
Example
public class StringDemo {
public static void main(String args[]) {
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println( helloString );
}
}
This will produce the following result −
Output
hello.
Note − The String class is immutable, so that once it is created a String object cannot be
changed. If there is a necessity to make a lot of modifications to Strings of characters, then
you should use String Buffer & String Builder Classes.
String Length
Methods used to obtain information about an object are known as accessor methods. One
accessor method that you can use with strings is the length() method, which returns the
number of characters contained in the string object.
The following program is an example of length(), method String class.
Example
public class StringDemo {
public static void main(String args[]) {
String palindrome = "Dot saw I was Tod";](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-28-320.jpg)
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int len = palindrome.length();
System.out.println( "String Length is : " + len );
}
}
This will produce the following result −
Output
String Length is : 17
Concatenating Strings
The String class includes a method for concatenating two strings −
string1.concat(string2);
This returns a new string that is string1 with string2 added to it at the end. You can also use
the concat() method with string literals, as in −
"My name is ".concat("Zara");
Strings are more commonly concatenated with the + operator, as in −
"Hello," + " world" + "!"
which results in −
"Hello, world!"
Let us look at the following example −
Example
public class StringDemo {
public static void main(String args[]) {
String string1 = "saw I was ";
System.out.println("Dot " + string1 + "Tod");
}
}
This will produce the following result −
Output
Dot saw I was Tod
Creating Format Strings
You have printf() and format() methods to print output with formatted numbers. The String
class has an equivalent class method, format(), that returns a String object rather than a
PrintStream object.
Using String's static format() method allows you to create a formatted string that you can
reuse, as opposed to a one-time print statement. For example, instead of −](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-29-320.jpg)
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7 static String copyValueOf(char[] data)
Returns a String that represents the character sequence in the array specified.
8 static String copyValueOf(char[] data, int offset, int count)
Returns a String that represents the character sequence in the array specified.
9 boolean endsWith(String suffix)
Tests if this string ends with the specified suffix.
10 boolean equals(Object anObject)
Compares this string to the specified object.
11 boolean equalsIgnoreCase(String anotherString)
Compares this String to another String, ignoring case considerations.
12 byte getBytes()
Encodes this String into a sequence of bytes using the platform's default charset, storing
the result into a new byte array.
13 byte[] getBytes(String charsetName)
Encodes this String into a sequence of bytes using the named charset, storing the result
into a new byte array.
14 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Copies characters from this string into the destination character array.
15 int hashCode()
Returns a hash code for this string.
16 int indexOf(int ch)
Returns the index within this string of the first occurrence of the specified character.
17 int indexOf(int ch, int fromIndex)](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-31-320.jpg)
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Tests if two string regions are equal.
28 boolean regionMatches(int toffset, String other, int ooffset, int len)
Tests if two string regions are equal.
29 String replace(char oldChar, char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string
with newChar.
30 String replaceAll(String regex, String replacement
Replaces each substring of this string that matches the given regular expression with the
given replacement.
31 String replaceFirst(String regex, String replacement)
Replaces the first substring of this string that matches the given regular expression with
the given replacement.
32 String[] split(String regex)
Splits this string around matches of the given regular expression.
33 String[] split(String regex, int limit)
Splits this string around matches of the given regular expression.
34 boolean startsWith(String prefix)
Tests if this string starts with the specified prefix.
35 boolean startsWith(String prefix, int toffset)
Tests if this string starts with the specified prefix beginning a specified index.
36 CharSequence subSequence(int beginIndex, int endIndex)
Returns a new character sequence that is a subsequence of this sequence.
37 String substring(int beginIndex)
Returns a new string that is a substring of this string.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-33-320.jpg)
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38 String substring(int beginIndex, int endIndex)
Returns a new string that is a substring of this string.
39 char[] toCharArray()
Converts this string to a new character array.
40 String toLowerCase()
Converts all of the characters in this String to lower case using the rules of the default
locale.
41 String toLowerCase(Locale locale)
Converts all of the characters in this String to lower case using the rules of the given
Locale.
42 String toString()
This object (which is already a string!) is itself returned.
43 String toUpperCase()
Converts all of the characters in this String to upper case using the rules of the default
locale.
44 String toUpperCase(Locale locale)
Converts all of the characters in this String to upper case using the rules of the given
Locale.
45 String trim()
Returns a copy of the string, with leading and trailing whitespace omitted.
46 static String valueOf(primitive data type x)
Returns the string representation of the passed data type argument.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-34-320.jpg)
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CONSTRUCTORS
A constructor initializes an object when it is created. It has the same name as its class and is
syntactically similar to a method. However, constructors have no explicit return type.
Typically, you will use a constructor to give initial values to the instance variables defined
by the class, or to perform any other start-up procedures required to create a fully formed
object.
All classes have constructors, whether you define one or not, because Java automatically
provides a default constructor that initializes all member variables to zero. However, once
you define your own constructor, the default constructor is no longer used.
Syntax
Following is the syntax of a constructor −
class ClassName {
ClassName() {
}
}
Java allows two types of constructors namely −
• No argument Constructors
• Parameterized Constructors
No argument Constructors
As the name specifies the no argument constructors of Java does not accept any parameters
instead, using these constructors the instance variables of a method will be initialized with
fixed values for all objects.
Example
Public class MyClass {
Int num;
MyClass() {
num = 100;
}
}
You would call constructor to initialize objects as follows
public class ConsDemo {
public static void main(String args[]) {
MyClass t1 = new MyClass();
MyClass t2 = new MyClass();
System.out.println(t1.num + " " + t2.num);
}](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-35-320.jpg)
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}
This would produce the following result
100 100
Parameterized Constructors
Most often, you will need a constructor that accepts one or more parameters. Parameters are
added to a constructor in the same way that they are added to a method, just declare them
inside the parentheses after the constructor's name.
Example
Here is a simple example that uses a constructor −
// A simple constructor.
class MyClass {
int x;
// Following is the constructor
MyClass(int i ) {
x = i;
}
}
You would call constructor to initialize objects as follows −
public class ConsDemo {
public static void main(String args[]) {
MyClass t1 = new MyClass( 10 );
MyClass t2 = new MyClass( 20 );
System.out.println(t1.x + " " + t2.x);
}
}
This would produce the following result −
10 20
JAVA OPERATORS
Java provides a rich set of operators to manipulate variables. We can divide all the Java
operators into the following groups −
• Arithmetic Operators
• Relational Operators
• Bitwise Operators
• Logical Operators
• Assignment Operators](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-36-320.jpg)
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|=
bitwise inclusive OR and assignment operator. C |= 2 is
same as C
= C | 2
Miscellaneous Operators
There are few other operators supported by Java Language.
Conditional Operator ( ? : )
Conditional operator is also known as the ternary operator. This operator consists of three
operands and is used to evaluate Boolean expressions. The goal of the operator is to decide,
which value should be assigned to the variable. The operator is written as −
variable x = (expression) ? value if true : value if false
Following is an example −
Example
public class Test {
public static void main(String args[]) {
int a, b;
a = 10;
b = (a == 1) ? 20: 30;
System.out.println( "Value of b is : " + b );
b = (a == 10) ? 20: 30;
System.out.println( "Value of b is : " + b );
}
}
This will produce the following result −
Output
Value of b is : 30
Value of b is : 20
instanceof Operator
This operator is used only for object reference variables. The operator checks whether the
object is of a particular type (class type or interface type). instanceof operator is written as −
( Object reference variable ) instanceof (class/interface type)
If the object referred by the variable on the left side of the operator passes the IS-A check for
the class/interface type on the right side, then the result will be true. Following is an
example −
Example](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-42-320.jpg)
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public class Test {
public static void main(String args[]) {
String name = "James";
// following will return true since name is type of String
boolean result = name instanceof String;
System.out.println( result );
}
}
This will produce the following result −
Output
true
This operator will still return true, if the object being compared is the assignment compatible
with the type on the right. Following is one more example −
Example
class Vehicle {}
public class Car extends Vehicle {
public static void main(String args[]) {
Vehicle a = new Car();
boolean result = a instanceof Car;
System.out.println( result );
}
}
This will produce the following result −
Output
true
PRECEDENCE OF JAVA OPERATORS
Operator precedence determines the grouping of terms in an expression. This affects how an
expression is evaluated. Certain operators have higher precedence than others; for example,
the multiplication operator has higher precedence than the addition operator −
For example, x = 7 + 3 * 2; here x is assigned 13, not 20 because operator * has higher
precedence than +, so it first gets multiplied with 3 * 2 and then adds into 7.
Here, operators with the highest precedence appear at the top of the table, those with the
lowest appear at the bottom. Within an expression, higher precedence operators will be
evaluated first.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-43-320.jpg)
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public static void main(String args[]) {
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ) {
System.out.print( x );
System.out.print(",");
}
System.out.print("n");
String [] names = {"James", "Larry", "Tom", "Lacy"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");
}
}
}
This will produce the following result −
Output
10, 20, 30, 40, 50,
James, Larry, Tom, Lacy,
JAVA - DECISION MAKING
Decision making structures have one or more conditions to be evaluated or tested by the
program, along with a statement or statements that are to be executed if the condition is
determined to be true, and optionally, other statements to be executed if the condition is
determined to be false.
Following is the general form of a typical decision making structure found in most of the
programming languages −](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-47-320.jpg)
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Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.
To determine the value of the whole expression, initially exp1 is evaluated.
• If the value of exp1 is true, then the value of Exp2 will be the value of the whole
expression.
• If the value of exp1 is false, then Exp3 is evaluated and its value becomes the value
of the entire expression.
JAVA - NUMBERS CLASS
Normally, when we work with Numbers, we use primitive data types such as byte, int, long,
double, etc.
Example
int i = 5000;
float gpa = 13.65;
double mask = 0xaf;
However, in development, we come across situations where we need to use objects instead
of primitive data types. In order to achieve this, Java provides wrapper classes.
All the wrapper classes (Integer, Long, Byte, Double, Float, Short) are subclasses of the
abstract class Number.
The object of the wrapper class contains or wraps its respective primitive data type.
Converting primitive data types into object is called boxing, and this is taken care by the
compiler. Therefore, while using a wrapper class you just need to pass the value of the
primitive data type to the constructor of the Wrapper class.
And the Wrapper object will be converted back to a primitive data type, and this process is
called unboxing. The Number class is part of the java.lang package.
Following is an example of boxing and unboxing −
Example
public class Test {
public static void main(String args[]) {
Integer x = 5; // boxes int to an Integer object
x = x + 10; // unboxes the Integer to a int
System.out.println(x);](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-49-320.jpg)
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// Unicode for uppercase Greek omega character
char uniChar = 'u039A';
// an array of chars
char[] charArray ={ 'a', 'b', 'c', 'd', 'e' };
However in development, we come across situations where we need to use objects instead of
primitive data types. In order to achieve this, Java provides wrapper class Character for
primitive data type char.
The Character class offers a number of useful class (i.e., static) methods for manipulating
characters. You can create a Character object with the Character constructor −
Character ch = new Character('a');
The Java compiler will also create a Character object for you under some circumstances. For
example, if you pass a primitive char into a method that expects an object, the compiler
automatically converts the char to a Character for you. This feature is called autoboxing or
unboxing, if the conversion goes the other way.
Example
// Here following primitive char 'a'
// is boxed into the Character object ch
Character ch = 'a';
// Here primitive 'x' is boxed for method test,
// return is unboxed to char 'c'
char c = test('x');
Escape Sequences
A character preceded by a backslash () is an escape sequence and has a special meaning to
the compiler.
The newline character (n) has been used frequently in this page in System.out.println()
statements to advance to the next line after the string is printed.
Following table shows the Java escape sequences −
Escape Sequence Description
t Inserts a tab in the text at this point.
b Inserts a backspace in the text at this point.
n Inserts a newline in the text at this point.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-53-320.jpg)
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r Inserts a carriage return in the text at this point.
f Inserts a form feed in the text at this point.
' Inserts a single quote character in the text at this point.
" Inserts a double quote character in the text at this point.
Inserts a backslash character in the text at this point.
When an escape sequence is encountered in a print statement, the compiler interprets it
accordingly.
Example
If you want to put quotes within quotes, you must use the escape sequence, ", on the interior
quotes −
public class Test {
public static void main(String args[]) {
System.out.println("She said "Hello!" to me.");
}
}
This will produce the following result −
Output
She said "Hello!" to me.
CHARACTER METHODS
Following is the list of the important instance methods that all the subclasses of the Character
class implement
Sr.No. Method & Description
1 isLetter()
Determines whether the specified char value is a letter.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-54-320.jpg)
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Returns a hash code for the invoking object.
9
void setTime(long time)
Sets the time and date as specified by time, which represents an elapsed time in
milliseconds from midnight, January 1, 1970.
10
String toString( )
Converts the invoking Date object into a string and returns the result.
Getting Current Date and Time
This is a very easy method to get current date and time in Java. You can use a simple Date
object with toString() method to print the current date and time as follows −
Example
import java.util.Date;
public class DateDemo {
public static void main(String args[]) {
// Instantiate a Date object
Date date = new Date();
// display time and date using toString()
System.out.println(date.toString());
}
}
This will produce the following result −
Output
on May 04 09:51:52 CDT 2009
Date Comparison
Following are the three ways to compare two dates −
• You can use getTime( ) to obtain the number of milliseconds that have elapsed since
midnight, January 1, 1970, for both objects and then compare these two values.
• You can use the methods before( ), after( ), and equals( ). Because the 12th of the
month comes before the 18th, for example, new Date(99, 2, 12).before(new Date
(99, 2, 18)) returns true.
• You can use the compareTo( ) method, which is defined by the Comparable interface
and implemented by Date.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-57-320.jpg)
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Date Formatting Using SimpleDateFormat
SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive
manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for
date-time formatting.
Example
import java.util.*;
import java.text.*;
public class DateDemo {
public static void main(String args[]) {
Date dNow = new Date( );
SimpleDateFormat ft =
new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("Current Date: " + ft.format(dNow));
}
}
This will produce the following result −
Output
Current Date: Sun 2004.07.18 at 04:14:09 PM PDT
Simple DateFormat Format Codes
To specify the time format, use a time pattern string. In this pattern, all ASCII letters are
reserved as pattern letters, which are defined as the following −
Character Description Example
G Era designator AD
y Year in four digits 2001
M Month in year July or 07
d Day in month 10](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-58-320.jpg)
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" Single quote `
Date Formatting Using printf
Date and time formatting can be done very easily using printf method. You use a two-letter
format, starting with t and ending in one of the letters of the table as shown in the following
code.
Example
import java.util.Date;
public class DateDemo {
public static void main(String args[]) {
// Instantiate a Date object
Date date = new Date();
// display time and date
String str = String.format("Current Date/Time : %tc", date );
System.out.printf(str);
}
}
This will produce the following result −
Output
Current Date/Time : Sat Dec 15 16:37:57 MST 2012
It would be a bit silly if you had to supply the date multiple times to format each part. For
that reason, a format string can indicate the index of the argument to be formatted.
The index must immediately follow the % and it must be terminated by a $.
Example
import java.util.Date;
public class DateDemo {
public static void main(String args[]) {
// Instantiate a Date object
Date date = new Date();
// display time and date
System.out.printf("%1$s %2$tB %2$td, %2$tY", "Due date:", date);
}
}
This will produce the following result −](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-60-320.jpg)
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Output
Due date: February 09, 2004
Alternatively, you can use the < flag. It indicates that the same argument as in the preceding
format specification should be used again.
Example
import java.util.Date;
public class DateDemo {
public static void main(String args[]) {
// Instantiate a Date object
Date date = new Date();
// display formatted date
System.out.printf("%s %tB %<te, %<tY", "Due date:", date);
}
}
This will produce the following result −
Output
Due date: February 09, 2004
Date and Time Conversion Characters
Character Description Example
c Complete date and time
Mon May 04 09:51:52 CDT
2009
F ISO 8601 date 2004-02-09
D U.S. formatted date (month/day/year) 02/09/2004
T 24-hour time 18:05:19
r 12-hour time 06:05:19 pm
R 24-hour time, no seconds 18:05](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-61-320.jpg)
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public class DateDemo {
public static void main(String args[]) {
SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd");
String input = args.length == 0 ? "1818-11-11" : args[0];
System.out.print(input + " Parses as ");
Date t;
try {
t = ft.parse(input);
System.out.println(t);
} catch (ParseException e) {
System.out.println("Unparseable using " + ft);
}
}
}
A sample run of the above program would produce the following result −
Output
1818-11-11 Parses as Wed Nov 11 00:00:00 EST 1818
Sleeping for a While
You can sleep for any period of time from one millisecond up to the lifetime of your
computer. For example, the following program would sleep for 3 seconds −
Example
import java.util.*;
public class SleepDemo {
public static void main(String args[]) {
try {
System.out.println(new Date( ) + "n");
Thread.sleep(5*60*10);
System.out.println(new Date( ) + "n");
} catch (Exception e) {
System.out.println("Got an exception!");
}
}
}
This will produce the following result −
Output
Sun May 03 18:04:41 GMT 2009
Sun May 03 18:04:51 GMT 2009
Measuring Elapsed Time](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-64-320.jpg)
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Sometimes, you may need to measure point in time in milliseconds. So let's re-write the
above example once again −
Example
import java.util.*;
public class DiffDemo {
public static void main(String args[]) {
try {
long start = System.currentTimeMillis( );
System.out.println(new Date( ) + "n");
Thread.sleep(5*60*10);
System.out.println(new Date( ) + "n");
long end = System.currentTimeMillis( );
long diff = end - start;
System.out.println("Difference is : " + diff);
} catch (Exception e) {
System.out.println("Got an exception!");
}
}
}
This will produce the following result −
Output
Sun May 03 18:16:51 GMT 2009
Sun May 03 18:16:57 GMT 2009
Difference is : 5993
GregorianCalendar Class
GregorianCalendar is a concrete implementation of a Calendar class that implements the
normal Gregorian calendar with which you are familiar. We did not discuss Calendar class
in this page, you can look up standard Java documentation for this.
The getInstance( ) method of Calendar returns a GregorianCalendar initialized with the
current date and time in the default locale and time zone. GregorianCalendar defines two
fields: AD and BC. These represent the two eras defined by the Gregorian calendar.
There are also several constructors for GregorianCalendar objects −
Sr.No. Constructor & Description
1
GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-65-320.jpg)
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Sets the GregorianCalendar change date.
24
void setTime(Date date)
Sets this Calendar's current time with the given Date.
25
void setTimeInMillis(long millis)
Sets this Calendar's current time from the given long value.
26
void setTimeZone(TimeZone value)
Sets the time zone with the given time zone value.
27
String toString()
Returns a string representation of this calendar.
Example
import java.util.*;
public class GregorianCalendarDemo {
public static void main(String args[]) {
String months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep",
"Oct", "Nov", "Dec"};
int year;
// Create a Gregorian calendar initialized
// with the current date and time in the
// default locale and timezone.
GregorianCalendar gcalendar = new GregorianCalendar();
// Display current time and date information.
System.out.print("Date: ");
System.out.print(months[gcalendar.get(Calendar.MONTH)]);
System.out.print(" " + gcalendar.get(Calendar.DATE) + " ");
System.out.println(year = gcalendar.get(Calendar.YEAR));
System.out.print("Time: ");
System.out.print(gcalendar.get(Calendar.HOUR) + ":");
System.out.print(gcalendar.get(Calendar.MINUTE) + ":");
System.out.println(gcalendar.get(Calendar.SECOND));
// Test if the current year is a leap year
if(gcalendar.isLeapYear(year)) {](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-69-320.jpg)
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• returnType − Method may return a value.
• nameOfMethod − This is the method name. The method signature consists of the
method name and the parameter list.
• Parameter List − The list of parameters, it is the type, order, and number of
parameters of a method. These are optional, method may contain zero parameters.
• method body − The method body defines what the method does with the statements.
Example
Here is the source code of the above defined method called min(). This method takes two
parameters num1 and num2 and returns the maximum between the two −
/** the snippet returns the minimum between two numbers */
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
Method Calling
For using a method, it should be called. There are two ways in which a method is called i.e.,
method returns a value or returning nothing (no return value).
The process of method calling is simple. When a program invokes a method, the program
control gets transferred to the called method. This called method then returns control to the
caller in two conditions, when −
• the return statement is executed.
• it reaches the method ending closing brace.
The methods returning void is considered as call to a statement. Lets consider an example −
System.out.println("This is pagespoint.com!");
The method returning value can be understood by the following example −
int result = sum(6, 9);
Following is the example to demonstrate how to define a method and how to call it −
Example
public class ExampleMinNumber {
public static void main(String[] args) {](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-71-320.jpg)
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int a = 11;
int b = 6;
int c = minFunction(a, b);
System.out.println("Minimum Value = " + c);
}
/** returns the minimum of two numbers */
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
}
This will produce the following result −
Output
Minimum value = 6
The void Keyword
The void keyword allows us to create methods which do not return a value. Here, in the
following example we're considering a void method methodRankPoints. This method is a
void method, which does not return any value. Call to a void method must be a statement
i.e. methodRankPoints(255.7);. It is a Java statement which ends with a semicolon as shown
in the following example.
Example
public class ExampleVoid {
public static void main(String[] args) {
methodRankPoints(255.7);
}
public static void methodRankPoints(double points) {
if (points >= 202.5) {
System.out.println("Rank:A1");
}else if (points >= 122.4) {
System.out.println("Rank:A2");
}else {
System.out.println("Rank:A3");
}
}
}](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-72-320.jpg)
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This will produce the following result −
Output
Rank:A1
Passing Parameters by Value
While working under calling process, arguments is to be passed. These should be in the
same order as their respective parameters in the method specification. Parameters can be
passed by value or by reference.
Passing Parameters by Value means calling a method with a parameter. Through this, the
argument value is passed to the parameter.
Example
The following program shows an example of passing parameter by value. The values of the
arguments remains the same even after the method invocation.
public class swappingExample {
public static void main(String[] args) {
int a = 30;
int b = 45;
System.out.println("Before swapping, a = " + a + " and b = " + b);
// Invoke the swap method
swapFunction(a, b);
System.out.println("n**Now, Before and After swapping values will be same here**:");
System.out.println("After swapping, a = " + a + " and b is " + b);
}
public static void swapFunction(int a, int b) {
System.out.println("Before swapping(Inside), a = " + a + " b = " + b);
// Swap n1 with n2
int c = a;
a = b;
b = c;
System.out.println("After swapping(Inside), a = " + a + " b = " + b);
}
}
This will produce the following result −
Output
Before swapping, a = 30 and b = 45
Before swapping(Inside), a = 30 b = 45
After swapping(Inside), a = 45 b = 30](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-73-320.jpg)
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**Now, Before and After swapping values will be same here**:
After swapping, a = 30 and b is 45
METHOD OVERLOADING
When a class has two or more methods by the same name but different parameters, it is
known as method overloading. It is different from overriding. In overriding, a method has
the same method name, type, number of parameters, etc.
Let’s consider the example discussed earlier for finding minimum numbers of integer type.
If, let’s say we want to find the minimum number of double type. Then the concept of
overloading will be introduced to create two or more methods with the same name but
different parameters.
The following example explains the same −
Example
public class ExampleOverloading {
public static void main(String[] args) {
int a = 11;
int b = 6;
double c = 7.3;
double d = 9.4;
int result1 = minFunction(a, b);
// same function name with different parameters
double result2 = minFunction(c, d);
System.out.println("Minimum Value = " + result1);
System.out.println("Minimum Value = " + result2);
}
// for integer
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
// for double
public static double minFunction(double n1, double n2) {
double min;
if (n1 > n2)
min = n2;
else](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-74-320.jpg)
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min = n1;
return min;
}
}
This will produce the following result −
Output
Minimum Value = 6
Minimum Value = 7.3
Overloading methods makes program readable. Here, two methods are given by the same
name but with different parameters. The minimum number from integer and double types is
the result.
Using Command-Line Arguments
Sometimes you will want to pass some information into a program when you run it. This is
accomplished by passing command-line arguments to main( ).
A command-line argument is the information that directly follows the program's name on
the command line when it is executed. To access the command-line arguments inside a Java
program is quite easy. They are stored as strings in the String array passed to main( ).
Example
The following program displays all of the command-line arguments that it is called with −
public class CommandLine {
public static void main(String args[]) {
for(int i = 0; i<args.length; i++) {
System.out.println("args[" + i + "]: " + args[i]);
}
}
}
Try executing this program as shown here −
$java CommandLine this is a command line 200 -100
This will produce the following result −
Output
args[0]: this
args[1]: is
args[2]: a
args[3]: command
args[4]: line
args[5]: 200
args[6]: -100](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-75-320.jpg)
![SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603.
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This_Example() {
System.out.println("This is an example program on keyword this");
}
This_Example(int num) {
// Invoking the default constructor
this();
// Assigning the local variable num to the instance variable num
this.num = num;
}
public void greet() {
System.out.println("Hi Welcome to Pagespoint");
}
public void print() {
// Local variable num
int num = 20;
// Printing the local variable
System.out.println("value of local variable num is : "+num);
// Printing the instance variable
System.out.println("value of instance variable num is : "+this.num);
// Invoking the greet method of a class
this.greet();
}
public static void main(String[] args) {
// Instantiating the class
This_Example obj1 = new This_Example();
// Invoking the print method
obj1.print();
// Passing a new value to the num variable through parametrized constructor
This_Example obj2 = new This_Example(30);
// Invoking the print method again
obj2.print();
}
}
This will produce the following result −
Output
This is an example program on keyword this](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-77-320.jpg)
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value of local variable num is : 20
value of instance variable num is : 10
Hi Welcome to Pagespoint
This is an example program on keyword this
value of local variable num is : 20
value of instance variable num is : 30
Hi Welcome to Pagespoint
Variable Arguments(var-args)
JDK 1.5 enables you to pass a variable number of arguments of the same type to a method.
The parameter in the method is declared as follows −
typeName... parameterName
In the method declaration, you specify the type followed by an ellipsis (...). Only one
variable-length parameter may be specified in a method, and this parameter must be the last
parameter. Any regular parameters must precede it.
Example
public class VarargsDemo {
public static void main(String args[]) {
// Call method with variable args
printMax(34, 3, 3, 2, 56.5);
printMax(new double[]{1, 2, 3});
}
public static void printMax( double... numbers) {
if (numbers.length == 0) {
System.out.println("No argument passed");
return;
}
double result = numbers[0];
for (int i = 1; i < numbers.length; i++)
if (numbers[i] > result)
result = numbers[i];
System.out.println("The max value is " + result);
}
}
This will produce the following result −
Output
The max value is 56.5
The max value is 3.0
The finalize( ) Method](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-78-320.jpg)
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If a package statement is not used then the class, interfaces, enumerations, and annotation
types will be placed in the current default package.
To compile the Java programs with package statements, you have to use -d option as shown
below.
javac -d Destination_folder file_name.java
Then a folder with the given package name is created in the specified destination, and the
compiled class files will be placed in that folder.
Example
Let us look at an example that creates a package called animals. It is a good practice to use
names of packages with lower case letters to avoid any conflicts with the names of classes
and interfaces.
Following package example contains interface named animals −
/* File name : Animal.java */
package animals;
interface Animal {
public void eat();
public void travel();
}
Now, let us implement the above interface in the same package animals −
package animals;
/* File name : MammalInt.java */
public class MammalInt implements Animal {
public void eat() {
System.out.println("Mammal eats");
}
public void travel() {
System.out.println("Mammal travels");
}
public int noOfLegs() {
return 0;
}
public static void main(String args[]) {
MammalInt m = new MammalInt();
m.eat();
m.travel();
}
}](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-80-320.jpg)
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Example of static variable
1. //Java Program to demonstrate the use of static variable
2. class Student{
3. int rollno;//instance variable
4. String name;
5. static String college ="ITS";//static variable
6. //constructor
7. Student(int r, String n){
8. rollno = r;
9. name = n;
10. }
11. //method to display the values
12. void display (){System.out.println(rollno+" "+name+" "+college);}
13. }
14. //Test class to show the values of objects
15. public class TestStaticVariable1{
16. public static void main(String args[]){
17. Student s1 = new Student(111,"Karan");
18. Student s2 = new Student(222,"Aryan");
19. //we can change the college of all objects by the single line of code
20. //Student.college="BBDIT";
21. s1.display();
22. s2.display();
23. }
24. }
Output:
111 Karan ITS
222 Aryan ITS
Program of the counter without static variable
In this example, we have created an instance variable named count which is incremented in
the constructor. Since instance variable gets the memory at the time of object creation, each
object will have the copy of the instance variable. If it is incremented, it won't reflect other
objects. So each object will have the value 1 in the count variable.
1. //Java Program to demonstrate the use of an instance variable
2. //which get memory each time when we create an object of the class.
3. class Counter{
4. int count=0;//will get memory each time when the instance is created
5.
6. Counter(){](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-86-320.jpg)
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7. count++;//incrementing value
8. System.out.println(count);
9. }
10.
11. public static void main(String args[]){
12. //Creating objects
13. Counter c1=new Counter();
14. Counter c2=new Counter();
15. Counter c3=new Counter();
16. }
17. }
Output:
1
1
1
Program of counter by static variable
As we have mentioned above, static variable will get the memory only once, if any object
changes the value of the static variable, it will retain its value.
1. //Java Program to illustrate the use of static variable which
2. //is shared with all objects.
3. class Counter2{
4. static int count=0;//will get memory only once and retain its value
5.
6. Counter2(){
7. count++;//incrementing the value of static variable
8. System.out.println(count);
9. }
10.
11. public static void main(String args[]){
12. //creating objects
13. Counter2 c1=new Counter2();
14. Counter2 c2=new Counter2();
15. Counter2 c3=new Counter2();
16. }
17. }
Output:](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-87-320.jpg)
![SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603.
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1
2
3
2) Java static method
If you apply static keyword with any method, it is known as static method.
o A static method belongs to the class rather than the object of a class.
o A static method can be invoked without the need for creating an instance of a class.
o A static method can access static data member and can change the value of it.
Example of static method
1. //Java Program to demonstrate the use of a static method.
2. class Student{
3. int rollno;
4. String name;
5. static String college = "ITS";
6. //static method to change the value of static variable
7. static void change(){
8. college = "BBDIT";
9. }
10. //constructor to initialize the variable
11. Student(int r, String n){
12. rollno = r;
13. name = n;
14. }
15. //method to display values
16. void display(){System.out.println(rollno+" "+name+" "+college);}
17. }
18. //Test class to create and display the values of object
19. public class TestStaticMethod{
20. public static void main(String args[]){
21. Student.change();//calling change method
22. //creating objects
23. Student s1 = new Student(111,"Karan");
24. Student s2 = new Student(222,"Aryan");
25. Student s3 = new Student(333,"Sonoo");
26. //calling display method
27. s1.display();
28. s2.display();
29. s3.display();
30. }](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-88-320.jpg)
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89
31. }
Output:111 Karan BBDIT
222 Aryan BBDIT
333 Sonoo BBDIT
Another example of a static method that performs a normal calculation
1. //Java Program to get the cube of a given number using the static method
2.
3. class Calculate{
4. static int cube(int x){
5. return x*x*x;
6. }
7.
8. public static void main(String args[]){
9. int result=Calculate.cube(5);
10. System.out.println(result);
11. }
12. }
Output:125
Restrictions for the static method
There are two main restrictions for the static method. They are:
1. The static method can not use non static data member or call non-static method
directly.
2. this and super cannot be used in static context.
1. class A{
2. int a=40;//non static
3.
4. public static void main(String args[]){
5. System.out.println(a);
6. }
7. }
Output:Compile Time Error
Q) Why is the Java main method static?
Ans) It is because the object is not required to call a static method. If it were a non-static
method, JVM creates an object first then call main() method that will lead the problem of
extra memory allocation.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-89-320.jpg)
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3) Java static block
o Is used to initialize the static data member.
o It is executed before the main method at the time of classloading.
Example of static block
1. class A2{
2. static{System.out.println("static block is invoked");}
3. public static void main(String args[]){
4. System.out.println("Hello main");
5. }
6. }
Output:static block is invoked
Hello main
Q) Can we execute a program without main() method?
Ans) No, one of the ways was the static block, but it was possible till JDK 1.6. Since JDK
1.7, it is not possible to execute a Java class without the main method.
1. class A3{
2. static{
3. System.out.println("static block is invoked");
4. System.exit(0);
5. }
6. }
Output:
static block is invoked
Since JDK 1.7 and above, output would be:
Error: Main method not found in class A3, please define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
METHOD OVERLOADING
In Java, two or more methods can have same name if they differ in parameters (different
number of parameters, different types of parameters, or both). These methods are called
overloaded methods and this feature is called method overloading. For example:](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-90-320.jpg)
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private static void display(int a, int b){
System.out.println("Arguments: " + a + " and " + b);
}
public static void main(String[] args) {
display(1);
display(1, 4);
}
}
Output:
Arguments: 1
Arguments: 1 and 4
2. By changing the datatype of parameters
class MethodOverloading {
// this method accepts int
private static void display(int a){
System.out.println("Got Integer data.");
}
// this method accepts String object
private static void display(String a){
System.out.println("Got String object.");
}
public static void main(String[] args) {
display(1);
display("Hello");
}
}
Output:
Got Integer data.
Got String object.
Here, both overloaded methods accept one argument. However, one accepts the argument of
type int whereas other accepts String object.
Let’s look at a real-world example:](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-92-320.jpg)
![SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603.
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class HelperService {
private String formatNumber(int value) {
return String.format("%d", value);
}
private String formatNumber(double value) {
return String.format("%.3f", value);
}
private String formatNumber(String value) {
return String.format("%.2f", Double.parseDouble(value));
}
public static void main(String[] args) {
HelperService hs = new HelperService();
System.out.println(hs.formatNumber(500));
System.out.println(hs.formatNumber(89.9934));
System.out.println(hs.formatNumber("550"));
}
}
When you run the program, the output will be:
500
89.993
550.00
Note: In Java, you can also overload constructors in a similar way like methods.
Recommended Reading: Java Constructor Overloading
Important Points
• Two or more methods can have same name inside the same class if they accept different
arguments. This feature is known as method overloading.
• Method overloading is achieved by either:
o changing the number of arguments.
o or changing the datatype of arguments.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-93-320.jpg)
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Simple Example of Java Enum
1. class EnumExample1{
2. //defining the enum inside the class
3. public enum Season { WINTER, SPRING, SUMMER, FALL }
4. //main method
5. public static void main(String[] args) {
6. //traversing the enum
7. for (Season s : Season.values())
8. System.out.println(s);
9. }}
Output:
WINTER
SPRING
SUMMER
FALL
Let us see another example of Java enum where we are using value(), valueOf(), and
ordinal() methods of Java enum.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-95-320.jpg)
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1. class EnumExample1{
2. //defining enum within class
3. public enum Season { WINTER, SPRING, SUMMER, FALL }
4. //creating the main method
5. public static void main(String[] args) {
6. //printing all enum
7. for (Season s : Season.values()){
8. System.out.println(s);
9. }
10. System.out.println("Value of WINTER is: "+Season.valueOf("WINTER"));
11. System.out.println("Index of WINTER is: "+Season.valueOf("WINTER").ordinal());
12. System.out.println("Index of SUMMER is: "+Season.valueOf("SUMMER").ordinal());
13.
14. }}
Output:
WINTER
SPRING
SUMMER
FALL
Value of WINTER is: WINTER
Index of WINTER is: 0
Index of SUMMER is: 2
Note: Java compiler internally adds values(), valueOf() and ordinal() methods within the
enum at compile time. It internally creates a static and final class for the enum.
What is the purpose of the values() method in the enum?
The Java compiler internally adds the values() method when it creates an enum. The values()
method returns an array containing all the values of the enum.
What is the purpose of the valueOf() method in the enum?
The Java compiler internally adds the valueOf() method when it creates an enum. The
valueOf() method returns the value of given constant enum.
What is the purpose of the ordinal() method in the enum?
The Java compiler internally adds the ordinal() method when it creates an enum. The
ordinal() method returns the index of the enum value.](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-96-320.jpg)
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Defining Java Enum
The enum can be defined within or outside the class because it is similar to a class. The
semicolon (;) at the end of the enum constants are optional. For example:
1. enum Season { WINTER, SPRING, SUMMER, FALL }
Or,
1. enum Season { WINTER, SPRING, SUMMER, FALL; }
Both the definitions of Java enum are the same.
Java Enum Example: Defined outside class
1. enum Season { WINTER, SPRING, SUMMER, FALL }
2. class EnumExample2{
3. public static void main(String[] args) {
4. Season s=Season.WINTER;
5. System.out.println(s);
6. }}
Output:
WINTER
Java Enum Example: Defined inside class
1. class EnumExample3{
2. enum Season { WINTER, SPRING, SUMMER, FALL; }//semicolon(;) is optional here
3. public static void main(String[] args) {
4. Season s=Season.WINTER;//enum type is required to access WINTER
5. System.out.println(s);
6. }}
Output:
WINTER
Java Enum Example: main method inside Enum
If you put main() method inside the enum, you can run the enum directly.
1. enum Season {
2. WINTER, SPRING, SUMMER, FALL;
3. public static void main(String[] args) {
4. Season s=Season.WINTER;
5. System.out.println(s);](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-97-320.jpg)
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6. }
7. }
Output:
WINTER
Initializing specific values to the enum constants
The enum constants have an initial value which starts from 0, 1, 2, 3, and so on. But, we can
initialize the specific value to the enum constants by defining fields and constructors. As
specified earlier, Enum can have fields, constructors, and methods.
Example of specifying initial value to the enum constants
1. class EnumExample4{
2. enum Season{
3. WINTER(5), SPRING(10), SUMMER(15), FALL(20);
4.
5. private int value;
6. private Season(int value){
7. this.value=value;
8. }
9. }
10. public static void main(String args[]){
11. for (Season s : Season.values())
12. System.out.println(s+" "+s.value);
13.
14. }}
15.
Output:
WINTER 5
SPRING 10
SUMMER 15
FALL 20
1. enum Season{
2. WINTER(10),SUMMER(20);
3. private int value;
4. Season(int value){
5. this.value=value;
6. }](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-98-320.jpg)
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7. }
Internal code generated by the compiler for the above example of enum type
1. final class Season extends Enum
2. {
3. public static Season[] values()
4. {
5. return (Season[])$VALUES.clone();
6. }
7. public static Season valueOf(String s)
8. {
9. return (Season)Enum.valueOf(Season, s);
10. }
11. private Season(String s, int i, int j)
12. {
13. super(s, i);
14. value = j;
15. }
16. public static final Season WINTER;
17. public static final Season SUMMER;
18. private int value;
19. private static final Season $VALUES[];
20. static
21. {
22. WINTER = new Season("WINTER", 0, 10);
23. SUMMER = new Season("SUMMER", 1, 20);
24. $VALUES = (new Season[] {
25. WINTER, SUMMER
26. });
27. }
28. }
Java Enum in a switch statement
We can apply enum on switch statement as in the given example:
Example of applying Enum on a switch statement
1. class EnumExample5{
2. enum Day{ SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, S
ATURDAY}
3. public static void main(String args[]){
4. Day day=Day.MONDAY;](https://image.slidesharecdn.com/javabookbysivasankari-201010141315/85/JAVA-BOOK-BY-SIVASANKARI-99-320.jpg)
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- 1. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 1 PROGRAMMING IN JAVA Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. HISTORY OF JAVA Java was originally designed for interactive television, but it was too advanced technology for the digital cable television industry at the time. The history of Java starts with the Green Team. Java team members (also known as Green Team), initiated this project to develop a language for digital devices such as set-top boxes, televisions, etc. However, it was suited for internet programming. Later, Java technology was incorporated by Netscape. The principles for creating Java programming were "Simple, Robust, Portable, Platform-independent, Secured, High Performance, Multithreaded, Architecture Neutral, Object-Oriented, Interpreted, and Dynamic". Java was developed by James Gosling, who is known as the father of Java, in 1995. James Gosling and his team members started the project in the early '90s. James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team of sun engineers called Green Team.Initially designed for small, embedded systems in electronic appliances like set-top boxes. Firstly, it was called "Greentalk" by James Gosling, and the file extension was .gt. After that, it was called Oak and was developed as a part of the Green project.Oak is a symbol of strength and chosen as a national tree of many countries like the U.S.A., France, Germany, Romania, etc.In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies. JDK 1.0 released in(January 23, 1996). After the first release of Java, there have been many additional features added to the language. Now Java is being used in Windows applications, Web applications, enterprise applications, mobile applications, cards, etc. Each new version adds the new features in Java. Java Version 1. JDK Alpha and Beta (1995) 2. JDK 1.0 (23rd Jan 1996) 3. JDK 1.1 (19th Feb 1997) 4. J2SE 1.2 (8th Dec 1998) 5. J2SE 1.3 (8th May 2000) 6. J2SE 1.4 (6th Feb 2002) 7. J2SE 5.0 (30th Sep 2004) 8. Java SE 6 (11th Dec 2006) 9. Java SE 7 (28th July 2011) 10. Java SE 8 (18th Mar 2014)
- 2. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 2 11. Java SE 9 (21st Sep 2017) 12. Java SE 10 (20th Mar 2018) For performing the examples discussed ,we will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM (128 MB of RAM recommended). We will also need the following software’s − • Linux 7.1 or Windows xp/7/8 operating system • Java JDK 8 ❖ Microsoft Notepad or any other text editor Java is developed by James Gosling at Sun Micro system in the year 1991. ❖ Initially it was named “OAK”. ❖ Java is case sensitive. Example: System.in ❖ Java was not the internet but also used in internet. ❖ It is a platform independent language. ❖ It is used to create a software on electronic device. Example: Microwave Oven, Remote Control. ❖ Java programs run in variety of CPU and different environments. IMPORTANCE OF JAVA: ❖ Java is forefront of program. ❖ Java expends the universe of object. We can access and create Object University. ❖ Client and server process also access in java. ❖ It is divided into 3 performance ▪ Passive ▪ Dynamic ▪ Active APPLET AND APPLICATIONS: ❖ Java divided into applet and applications. ❖ Applications having Animations is called applets. APPLICATIONS: ❖ It is a program that runs on our computer under the operating system of that computer. Example: C, C++, Java APPLETS: ❖ It is an application designed to be transmitted over the internet and executed by a java compatible with browser. ❖ It is an intelligence program.
- 3. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 3 Example: sound, Image, Video clips. SECURITY: ❖ To avoid the viral infection. Use security. Example: Firewall method, K7, Trojan Horse. PORTABILITY: ❖ Many type of computers and operating system are in use throughout the world and many are connected to the internet. ❖ It is elegant and efficient. Difference between JDK, JRE, and JVM 1. A summary of JVM 2. Java Runtime Environment (JRE) 3. Java Development Kit (JDK) JVM JVM (Java Virtual Machine) is an abstract machine. It is called a virtual machine because it doesn't physically exist. It is a specification that provides a runtime environment in which Java byte code can be executed. It can also run those programs which are written in other languages and compiled to Java byte code. JVMs are available for many hardware and software platforms. JVM, JRE, and JDK are platform dependent because the configuration of each OS is different from each other. However, Java is platform independent. There are three notions of the JVM: specification, implementation, and instance. The JVM performs the following main tasks: o Loads code o Verifies code o Executes code o Provides runtime environment
- 4. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 4 JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java byte code can be executed. JVMs are available for many hardware and software platforms (i.e. JVM is platform dependent). What is JVM It is: 1. A specification where working of Java Virtual Machine is specified. But implementation provider is independent to choose the algorithm. Its implementation has been provided by Oracle and other companies. 2. An implementation Its implementation is known as JRE (Java Runtime Environment). 3. Runtime Instance Whenever you write java command on the command prompt to run the java class, an instance of JVM is created. JVM provides definitions for the: o Memory area o Class file format o Register set o Garbage-collected heap o Fatal error reporting etc. Local Environment Setup If you are still willing to set up your environment for Java programming language, then this section guides you on how to download and set up Java on your machine. Following are the steps to set up the environment. Java SE is freely available from the link Download Java. You can download a version based on your operating system.
- 5. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 5 Follow the instructions to download Java and run the .exe to install Java on your machine. Once you installed Java on your machine, you will need to set environment variables to point to correct installation directories − Setting Up the Path for Windows Assuming you have installed Java in c:Program Filesjavajdk directory − • Right-click on 'My Computer' and select 'Properties'. • Click the 'Environment variables' button under the 'Advanced' tab. • Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:WINDOWSSYSTEM32', then change your path to read 'C:WINDOWSSYSTEM32;c:Program Filesjavajdkbin'. Setting Up the Path for Linux, UNIX, Solaris, FreeBSD Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation, if you have trouble doing this. Example, if you use bash as your shell, then you would add the following line to the end of your '.bashrc: export PATH = /path/to/java:$PATH' Popular Java Editors To write your Java programs, you will need a text editor. There are even more sophisticated IDEs available in the market. But for now, you can consider one of the following − • Notepad − On Windows machine, you can use any simple text editor like Notepad TextPad. • Netbeans − A Java IDE that is open-source and free which can be downloaded from https://www.netbeans.org/index.html. • Eclipse − A Java IDE developed by the eclipse open-source community. • Object Oriented − In Java, everything is an Object. Java can be easily extended since it is based on the Object model. • Platform Independent − Unlike many other programming languages including C and C++, when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on. FEATURES OF JAVA The primary objective of Java programming language creation was to make it portable, simple and secure programming language. Apart from this, there are also some excellent features which play an important role in the popularity of this language. The features of Java are also known as java buzzwords. A list of most important features of Java language is given below
- 6. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 6 1. Simple 2. Object-Oriented 3. Portable 4. Platform independent 5. Secured 6. Robust 7. Architecture neutral 8. Interpreted 9. High Performance 10. Multithreaded 11. Distributed 12. Dynamic Simple Java is very easy to learn, and its syntax is simple, clean and easy to understand. According to Sun, Java language is a simple programming language because: o Java syntax is based on C++ (so easier for programmers to learn it after C++). o Java has removed many complicated and rarely-used features, for example, explicit pointers, operator overloading, etc. There is no need to remove unreferenced objects because there is an Automatic Garbage Collection in Java Object-oriented Java is an object-oriented programming language. Everything in Java is an object. Object-oriented means we organize our software as a combination of different types of objects that incorporates both data and behavior. Object-oriented programming (OOPs) is a methodology that simplifies software development and maintenance by providing some rules. Basic concepts of OOPs are: 1. Object 2. Class 3. Inheritance 4. Polymorphism 5. Abstraction
- 7. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 7 6. Encapsulation Platform Independent Java is platform independent because it is different from other languages like C, C++, etc. which are compiled into platform specific machines while Java is a write once, run anywhere language. A platform is the hardware or software environment in which a program runs. There are two types of platforms software-based and hardware-based. Java provides a software-based platform. The Java platform differs from most other platforms in the sense that it is a software-based platform that runs on the top of other hardware-based platforms. It has two components: 1. Runtime Environment 2. API(Application Programming Interface) Java code can be run on multiple platforms, for example, Windows, Linux, Sun Solaris, Mac/OS, etc. Java code is compiled by the compiler and converted into bytecode. This bytecode is a platform-independent code because it can be run on multiple platforms, i.e., Write Once and Run Anywhere(WORA). Secured Java is best known for its security. With Java, we can develop virus-free systems. Java is secured because: o No explicit pointer o Java Programs run inside a virtual machine sandbox o Classloader: Classloader in Java is a part of the Java Runtime Environment(JRE) which is used to load Java classes into the Java Virtual Machine dynamically. It adds security by separating the package for the classes of the local file system from those that are imported from network sources. o Bytecode Verifier: It checks the code fragments for illegal code that can violate access right to objects. o Security Manager: It determines what resources a class can access such as reading and writing to the local disk. o Java language provides these securities by default. Some security can also be provided by an application developer explicitly through SSL, JAAS, Cryptography, etc.
- 8. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 8 Robust Robust simply means strong. Java is robust because: o It uses strong memory management. o There is a lack of pointers that avoids security problems. o There is automatic garbage collection in java which runs on the Java Virtual Machine to get rid of objects which are not being used by a Java application anymore. o There are exception handling and the type checking mechanism in Java. All these points make Java robust. Architecture-neutral Java is architecture neutral because there are no implementation dependent features, for example, the size of primitive types is fixed. In C programming, int data type occupies 2 bytes of memory for 32-bit architecture and 4 bytes of memory for 64-bit architecture. However, it occupies 4 bytes of memory for both 32 and 64-bit architectures in Java Portable Java is portable because it facilitates you to carry the Java bytecode to any platform. It doesn't require any implementation High-performance Java is faster than other traditional interpreted programming languages because Java bytecode is "close" to native code. It is still a little bit slower than a compiled language (e.g., C++). Java is an interpreted language that is why it is slower than compiled languages, e.g., C, C++, etc.
- 9. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 9 Distributed Java is distributed because it facilitates users to create distributed applications in Java. RMI and EJB are used for creating distributed applications. This feature of Java makes us able to access files by calling the methods from any machine on the internet Multi-threaded A thread is like a separate program, executing concurrently. We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it doesn't occupy memory for each thread. It shares a common memory area. Threads are important for multi-media, Web applications, etc. Dynamic Java is a dynamic language. It supports dynamic loading of classes. It means classes are loaded on demand. It also supports functions from its native languages, i.e., C and C++. Java supports dynamic compilation and automatic memory management (garbage collection). The latest release of the Java Standard Edition is Java SE 8. With the advancement of Java and its widespread popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications, J2ME for Mobile Applications. The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere. CLASSES AND OBJECTS • Object − Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors – wagging the tail, barking, eating. An object is an instance of a class. • Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type support. Objects in Java Let us now look deep into what are objects. If we consider the real-world, we can find many objects around us, cars, dogs, humans, etc. All these objects have a state and a behavior. If we consider a dog, then its state is - name, breed, color, and the behavior is - barking, wagging the tail, running. If you compare the software object with a real-world object, they have very similar characteristics.
- 10. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 10 Software objects also have a state and a behavior. A software object's state is stored in fields and behavior is shown via methods. So in software development, methods operate on the internal state of an object and the object-to-object communication is done via methods. First Java Program | Hello World Example 1. Software Requirements 2. Creating Hello Java Example 3. Resolving javac is not recognized To create a simple java program, you need to create a class that contains the main method. Let's understand the requirement first. The requirement for Java , Welcome To Java Example For executing any java program, you need to o Install the JDK if you don't have installed it, download the JDK and install it. o Set path of the jdk/bin directory. http://www.javatpoint.com/how-to-set-path-in-java o Create the java program o Compile and run the java program SYNTAX OF CLASS: Class classname { Type instance variable 1; . . . Type instance variable N; Type methodname1(parameter list) { Body of the method } Type methodnameN(parameter list) { Body of the method } } Simple Program: Class Simple { public static void main(String args[])
- 11. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 11 { System.out.println(“Welcome to JAVA”); } } Compilation: C:> bin> javac Simple.java Run: C:> bin> java Simple Output: Welcome to JAVA Compilation Flow: When we compile Java program using javac tool, java compiler converts the source code into byte code CREATING AN OBJECT As mentioned previously, a class provides the blueprints for objects. So basically, an object is created from a class. In Java, the new keyword is used to create new objects. There are three steps when creating an object from a class − • Declaration − A variable declaration with a variable name with an object type. • Instantiation − The 'new' keyword is used to create the object. • Initialization − The 'new' keyword is followed by a call to a constructor. This call initializes the new object. DECLARING OBJECTS:
- 12. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 12 TWO TYPES Syntax of Object 1. Classname objectname=new classname() 2. Classname objectname; Objectname=new classname(); Example of Object Declaration 1. Box mybox=new Box()); 2. Box mybox; mybox=new box(); SAMPLE PROGRAM: Class box { Double width; Double height; Double depth; } Class boxdemo { public static void main(String args[]) box mybox=new box(); Double volume; Mybox.width=10; Mybox.height=20; Mybox.depth=15; Volume=mybox.width*mybox.height*mybox.depth; System.out.println(“The value is :”+ volume); } } JAVA - BASIC DATATYPES Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in the memory. Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables. There are two data types available in Java − • Primitive Data Types • Reference/Object Data Types Primitive Data Types
- 13. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 13 There are eight primitive datatypes supported by Java. Primitive datatypes are predefined by the language and named by a keyword. Let us now look into the eight primitive data types in detail. Data type long int short byte double float char Boolean Width 64 32 16 8 64 32 255 True/False byte • Byte data type is an 8-bit signed two's complement integer • Minimum value is -128 (-2^7) • Maximum value is 127 (inclusive)(2^7 -1) • Default value is 0 • Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an integer. • Example: byte a = 100, byte b = -50 short • Short data type is a 16-bit signed two's complement integer • Minimum value is -32,768 (-2^15) • Maximum value is 32,767 (inclusive) (2^15 -1) • Short data type can also be used to save memory as byte data type. A short is 2 times smaller than an integer • Default value is 0. • Example: short s = 10000, short r = -20000 int • Int data type is a 32-bit signed two's complement integer. • Minimum value is - 2,147,483,648 (-2^31)
- 14. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 14 • Maximum value is 2,147,483,647(inclusive) (2^31 -1) • Integer is generally used as the default data type for integral values unless there is a concern about memory. • The default value is 0 • Example: int a = 100000, int b = -200000 long • Long data type is a 64-bit signed two's complement integer • Minimum value is -9,223,372,036,854,775,808(-2^63) • Maximum value is 9,223,372,036,854,775,807 (inclusive)(2^63 -1) • This type is used when a wider range than int is needed • Default value is 0L • Example: long a = 100000L, long b = -200000L float • Float data type is a single-precision 32-bit IEEE 754 floating point • Float is mainly used to save memory in large arrays of floating point numbers • Default value is 0.0f • Float data type is never used for precise values such as currency • Example: float f1 = 234.5f double • double data type is a double-precision 64-bit IEEE 754 floating point • This data type is generally used as the default data type for decimal values, generally the default choice • Double data type should never be used for precise values such as currency • Default value is 0.0d • Example: double d1 = 123.4 boolean • boolean data type represents one bit of information • There are only two possible values: true and false • This data type is used for simple flags that track true/false conditions • Default value is false • Example: boolean one = true
- 15. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 15 char • char data type is a single 16-bit Unicode character • Minimum value is 'u0000' (or 0) • Maximum value is 'uffff' (or 65,535 inclusive) • Char data type is used to store any character • Example: char letterA = 'A' REFERENCE DATATYPES • Reference variables are created using defined constructors of the classes. They are used to access objects. These variables are declared to be of a specific type that cannot be changed. For example, Employee, Puppy, etc. • Class objects and various type of array variables come under reference datatype. • Default value of any reference variable is null. • A reference variable can be used to refer any object of the declared type or any compatible type. • Example: Animal animal = new Animal("giraffe"); LEXICAL ISSUES: o White space o Identifier o Literals o Commends o Separators o Java Keywords JAVA LITERALS A literal is a source code representation of a fixed value. They are represented directly in the code without any computation. Literals can be assigned to any primitive type variable. For example − byte a = 68; char a = 'A'; byte, int, long, and short can be expressed in decimal(base 10), hexadecimal(base 16) or octal(base 8) number systems as well. Prefix 0 is used to indicate octal, and prefix 0x indicates hexadecimal when using these number systems for literals. For example − int decimal = 100; int octal = 0144; int hexa = 0x64;
- 16. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 16 String literals in Java are specified like they are in most other languages by enclosing a sequence of characters between a pair of double quotes. Examples of string literals are − Example "Hello World" "twonlines" ""This is in quotes"" String and char types of literals can contain any Unicode characters. For example − char a = 'u0001'; String a = "u0001"; VARIABLE TYPES A variable provides us with named storage that our programs can manipulate. Each variable in Java has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable. You must declare all variables before they can be used. Following is the basic form of a variable declaration − data type variable [ = value][, variable [ = value] ...] ; Here data type is one of Java's datatypes and variable is the name of the variable. To declare more than one variable of the specified type, you can use a comma-separated list. Following are valid examples of variable declaration and initialization in Java − Example int a, b, c; // Declares three ints, a, b, and c. int a = 10, b = 10; // Example of initialization byte B = 22; // initializes a byte type variable B. double pi = 3.14159; // declares and assigns a value of PI. char a = 'a'; // the char variable a iis initialized with value 'a' This chapter will explain various variable types available in Java Language. There are three kinds of variables in Java − • Local variables • Instance variables • Class/Static variables Local Variables • Local variables are declared in methods, constructors, or blocks. • Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block.
- 17. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 17 • Access modifiers cannot be used for local variables. • Local variables are visible only within the declared method, constructor, or block. • Local variables are implemented at stack level internally. • There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use. Example Here, age is a local variable. This is defined inside pupAge() method and its scope is limited to only this method. public class Test { public void pupAge() { int age = 0; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]) { Test test = new Test(); test.pupAge(); } } This will produce the following result Output Puppy age is: 7 Instance Variables • Instance variables are declared in a class, but outside a method, constructor or any block. • When a space is allocated for an object in the heap, a slot for each instance variable value is created. • Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed. • Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object's state that must be present throughout the class. • Instance variables can be declared in class level before or after use. • Access modifiers can be given for instance variables. • The instance variables are visible for all methods, constructors and block in the class. Normally, it is recommended to make these variables private (access level).
- 18. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 18 However, visibility for subclasses can be given for these variables with the use of access modifiers. • Instance variables have default values. For numbers, the default value is 0, for Booleans it is false, and for object references it is null. Values can be assigned during the declaration or within the constructor. Instance variables can be accessed directly by calling the variable name inside the class. However, within static methods (when instance variables are given accessibility), they should be called using the fully qualified name. ObjectReference.VariableName import java.io.*; public class Employee { // this instance variable is visible for any child class. public String name; // salary variable is visible in Employee class only. private double salary; // The name variable is assigned in the constructor. public Employee (String empName) { name = empName; } // The salary variable is assigned a value. public void setSalary(double empSal) { salary = empSal; } // This method prints the employee details. public void printEmp() { System.out.println("name : " + name ); System.out.println("salary :" + salary); } public static void main(String args[]) { Employee empOne = new Employee("Ransika"); empOne.setSalary(1000); empOne.printEmp(); } } Output name : Ransika salary :1000.0 Class/Static Variables
- 19. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 19 • Class variables also known as static variables are declared with the static keyword in a class, but outside a method, constructor or a block. • There would only be one copy of each class variable per class, regardless of how many objects are created from it. • Static variables are rarely used other than being declared as constants. Constants are variables that are declared as public/private, final, and static. Constant variables never change from their initial value. • Static variables are stored in the static memory. It is rare to use static variables other than declared final and used as either public or private constants. • Static variables are created when the program starts and destroyed when the program stops. • Visibility is similar to instance variables. However, most static variables are declared public since they must be available for users of the class. • Default values are same as instance variables. For numbers, the default value is 0; for Booleans, it is false; and for object references, it is null. Values can be assigned during the declaration or within the constructor. Additionally, values can be assigned in special static initializer blocks. • Static variables can be accessed by calling with the class name ClassName.VariableName. • When declaring class variables as public static final, then variable names (constants) are all in upper case. If the static variables are not public and final, the naming syntax is the same as instance and local variables. import java.io.*; public class Employee { // salary variable is a private static variable private static double salary; // DEPARTMENT is a constant public static final String DEPARTMENT = "Development "; public static void main(String args[]) { salary = 1000; System.out.println(DEPARTMENT + "average salary:" + salary); }
- 20. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 20 } Output Development average salary:1000 MODIFIER TYPES Modifiers are keywords that you add to those definitions to change their meanings. Java language has a wide variety of modifiers, including the following − • Java Access Modifiers • Non Access Modifiers To use a modifier, you include its keyword in the definition of a class, method, or variable. The modifier precedes the rest of the statement, as in the following example. Example public class className { // ... } private boolean myFlag; static final double weeks = 9.5; protected static final int BOXWIDTH = 42; public static void main(String[] arguments) { // body of method } Access Control Modifiers Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are − • Visible to the package, the default. No modifiers are needed. • Visible to the class only (private). • Visible to the world (public). • Visible to the package and all subclasses (protected). Non-Access Modifiers Java provides a number of non-access modifiers to achieve many other functionality. • The static modifier for creating class methods and variables. • The final modifier for finalizing the implementations of classes, methods, and variables. • The abstract modifier for creating abstract classes and methods.
- 21. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 21 • The synchronized and volatile modifiers, which are used for threads. DYNAMIC INITIALIZATION: Class sample { Public static void main(String args[]) { int a=,b=4; //dynamic intialization int c=math.sqrt(a*a + b*b); System.out.println(“The value of c is “+c); } } Output: The value of c is: 5 TYPE CONVERSION AND CASTING: One data type automatically converted into another. Example: int a,b; float c; c=a+b; ARRAY AND ITS TYPES Group of elements and group of array is called array. ▪ One dimensional ▪ Two dimensional ▪ Multi dimensional Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.
- 22. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 22 Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. Declaring Array Variables To use an array in a program, you must declare a variable to reference the array, and you must specify the type of array the variable can reference. Here is the syntax for declaring an array variable − Syntax dataType[] arrayRefVar; // preferred way. or dataType arrayRefVar[]; // works but not preferred way. Note − The style dataType[] arrayRefVar is preferred. The style dataType arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate C/C++ programmers. Example The following code snippets are examples of this syntax − double[] myList; // preferred way. or double myList[]; // works but not preferred way. Creating Arrays You can create an array by using the new operator with the following syntax − Syntax arrayRefVar = new dataType[arraySize]; The above statement does two things − • It creates an array using new dataType[arraySize]. • It assigns the reference of the newly created array to the variable arrayRefVar. Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combined in one statement, as shown below − dataType[] arrayRefVar = new dataType[arraySize]; Alternatively you can create arrays as follows − dataType[] arrayRefVar = {value0, value1, ..., valuek}; The array elements are accessed through the index. Array indices are 0-based; that is, they start from 0 to arrayRefVar.length-1.
- 23. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 23 Example Following statement declares an array variable, myList, creates an array of 10 elements of double type and assigns its reference to myList − double[] myList = new double[10]; Following picture represents array myList. Here, myList holds ten double values and the indices are from 0 to 9. Processing Arrays When processing array elements, we often use either for loop or foreach loop because all of the elements in an array are of the same type and the size of the array is known. public class TestArray { public static void main(String[] args) { double[] myList = {1.9, 2.9, 3.4, 3.5}; // Print all the array elements for (int i = 0; i < myList.length; i++) { System.out.println(myList[i] + " "); } // Summing all elements double total = 0; for (int i = 0; i < myList.length; i++) { total += myList[i]; } System.out.println("Total is " + total); // Finding the largest element double max = myList[0]; for (int i = 1; i < myList.length; i++) { if (myList[i] > max) max = myList[i];
- 24. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 24 } System.out.println("Max is " + max); } } This will produce the following result − Output 1.9 2.9 3.4 3.5 Total is 11.7 Max is 3.5 Enhanced for loop in Java As of Java 5, the enhanced for loop was introduced. This is mainly used to traverse collection of elements including arrays. Syntax Following is the syntax of enhanced for loop − for(declaration : expression) { // Statements } • Declaration − The newly declared block variable, is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element. • Expression − This evaluates to the array you need to loop through. The expression can be an array variable or method call that returns an array. Example public class Test { public static void main(String args[]) { int [] numbers = {10, 20, 30, 40, 50}; for(int x : numbers ) { System.out.print( x ); System.out.print(","); } System.out.print("n"); String [] names = {"James", "Larry", "Tom", "Lacy"}; for( String name : names ) { System.out.print( name ); System.out.print(",");
- 25. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 25 } } } This will produce the following result − Output 10, 20, 30, 40, 50, James, Larry, Tom, Lacy, JAVA KEYWORDS Java keywords are also known as reserved words. Keywords are particular words which acts as a key to a code. These are predefined words by Java so it cannot be used as a variable or object name. List of Java Keywords A list of Java keywords or reserved words are given below: 1. abstract: Java abstract keyword is used to declare abstract class. Abstract class can provide the implementation of interface. It can have abstract and non-abstract methods. 2. boolean: Java boolean keyword is used to declare a variable as a boolean type. It can hold True and False values only. 3. break: Java break keyword is used to break loop or switch statement. It breaks the current flow of the program at specified condition. 4. byte: Java byte keyword is used to declare a variable that can hold an 8-bit data values. 5. case: Java case keyword is used to with the switch statements to mark blocks of text. 6. catch: Java catch keyword is used to catch the exceptions generated by try statements. It must be used after the try block only. 7. char: Java char keyword is used to declare a variable that can hold unsigned 16-bit Unicode characters 8. class: Java class keyword is used to declare a class. 9. continue: Java continue keyword is used to continue the loop. It continues the current flow of the program and skips the remaining code at the specified condition. 10. default: Java default keyword is used to specify the default block of code in a switch statement. 11. do: Java do keyword is used in control statement to declare a loop. It can iterate a part of the program several times.
- 26. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 26 12. double: Java double keyword is used to declare a variable that can hold a 64-bit floating-point numbers. 13. else: Java else keyword is used to indicate the alternative branches in an if statement. 14. enum: Java enum keyword is used to define a fixed set of constants. Enum constructors are always private or default. 15. extends: Java extends keyword is used to indicate that a class is derived from another class or interface. 16. final: Java final keyword is used to indicate that a variable holds a constant value. It is applied with a variable. It is used to restrict the user. 17. finally: Java finally keyword indicates a block of code in a try-catch structure. This block is always executed whether exception is handled or not. 18. float: Java float keyword is used to declare a variable that can hold a 32-bit floating- point number. 19. for: Java for keyword is used to start a for loop. It is used to execute a set of instructions/functions repeatedly when some conditions become true. If the number of iteration is fixed, it is recommended to use for loop. 20. if: Java if keyword tests the condition. It executes the if block if condition is true. 21. implements: Java implements keyword is used to implement an interface. 22. import: Java import keyword makes classes and interfaces available and accessible to the current source code. 23. instanceof: Java instanceof keyword is used to test whether the object is an instance of the specified class or implements an interface. 24. int: Java int keyword is used to declare a variable that can hold a 32-bit signed integer. 25. interface: Java interface keyword is used to declare an interface. It can have only abstract methods. 26. long: Java long keyword is used to declare a variable that can hold a 64-bit integer. 27. native: Java native keyword is used to specify that a method is implemented in native code using JNI (Java Native Interface). 28. new: Java new keyword is used to create new objects. 29. null: Java null keyword is used to indicate that a reference does not refer to anything. It removes the garbage value. 30. package: Java package keyword is used to declare a Java package that includes the classes. 31. private: Java private keyword is an access modifier. It is used to indicate that a method or variable may be accessed only in the class in which it is declared. 32. protected: Java protected keyword is an access modifier. It can be accessible within package and outside the package but through inheritance only. It can't be applied on the class.
- 27. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 27 33. public: Java public keyword is an access modifier. It is used to indicate that an item is accessible anywhere. It has the widest scope among all other modifiers. 34. return: Java return keyword is used to return from a method when its execution is complete. 35. short: Java short keyword is used to declare a variable that can hold a 16-bit integer. 36. static: Java static keyword is used to indicate that a variable or method is a class method. The static keyword in Java is used for memory management mainly. 37. strictfp: Java strictfp is used to restrict the floating-point calculations to ensure portability. 38. super: Java super keyword is a reference variable that is used to refer parent class object. It can be used to invoke immediate parent class method. 39. switch: The Java switch keyword contains a switch statement that executes code based on test value. The switch statement tests the equality of a variable against multiple values. 40. synchronized: Java synchronized keyword is used to specify the critical sections or methods in multithreaded code. 41. this: Java this keyword can be used to refer the current object in a method or constructor. 42. throw: The Java throw keyword is used to explicitly throw an exception. The throw keyword is mainly used to throw custom exception. It is followed by an instance. 43. throws: The Java throws keyword is used to declare an exception. Checked exception can be propagated with throws. 44. transient: Java transient keyword is used in serialization. If you define any data member as transient, it will not be serialized. 45. try: Java try keyword is used to start a block of code that will be tested for exceptions. The try block must be followed by either catch or finally block. 46. void: Java void keyword is used to specify that a method does not have a return value. 47. volatile: Java volatile keyword is used to indicate that a variable may change asynchronously. 48. while: Java while keyword is used to start a while loop. This loop iterates a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop
- 28. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 28 STRINGS CLASS Strings, which are widely used in Java programming, are a sequence of characters. In Java programming language, strings are treated as objects. The Java platform provides the String class to create and manipulate strings. Creating Strings The most direct way to create a string is to write − String greeting = "Hello world!"; Whenever it encounters a string literal in your code, the compiler creates a String object with its value in this case, "Hello world!'. As with any other object, you can create String objects by using the new keyword and a constructor. The String class has 11 constructors that allow you to provide the initial value of the string using different sources, such as an array of characters. Example public class StringDemo { public static void main(String args[]) { char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String(helloArray); System.out.println( helloString ); } } This will produce the following result − Output hello. Note − The String class is immutable, so that once it is created a String object cannot be changed. If there is a necessity to make a lot of modifications to Strings of characters, then you should use String Buffer & String Builder Classes. String Length Methods used to obtain information about an object are known as accessor methods. One accessor method that you can use with strings is the length() method, which returns the number of characters contained in the string object. The following program is an example of length(), method String class. Example public class StringDemo { public static void main(String args[]) { String palindrome = "Dot saw I was Tod";
- 29. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 29 int len = palindrome.length(); System.out.println( "String Length is : " + len ); } } This will produce the following result − Output String Length is : 17 Concatenating Strings The String class includes a method for concatenating two strings − string1.concat(string2); This returns a new string that is string1 with string2 added to it at the end. You can also use the concat() method with string literals, as in − "My name is ".concat("Zara"); Strings are more commonly concatenated with the + operator, as in − "Hello," + " world" + "!" which results in − "Hello, world!" Let us look at the following example − Example public class StringDemo { public static void main(String args[]) { String string1 = "saw I was "; System.out.println("Dot " + string1 + "Tod"); } } This will produce the following result − Output Dot saw I was Tod Creating Format Strings You have printf() and format() methods to print output with formatted numbers. The String class has an equivalent class method, format(), that returns a String object rather than a PrintStream object. Using String's static format() method allows you to create a formatted string that you can reuse, as opposed to a one-time print statement. For example, instead of −
- 30. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 30 Example System.out.printf("The value of the float variable is " + "%f, while the value of the integer " + "variable is %d, and the string " + "is %s", floatVar, intVar, stringVar); You can write − String fs; fs = String.format("The value of the float variable is " + "%f, while the value of the integer " + "variable is %d, and the string " + "is %s", floatVar, intVar, stringVar); System.out.println(fs); String Methods Here is the list of methods supported by String class − Sr.No. Method & Description 1 char charAt(int index) Returns the character at the specified index. 2 int compareTo(Object o) Compares this String to another Object. 3 int compareTo(String anotherString) Compares two strings lexicographically. 4 int compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences. 5 String concat(String str) Concatenates the specified string to the end of this string. 6 boolean contentEquals(StringBuffer sb) Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
- 31. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 31 7 static String copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified. 8 static String copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified. 9 boolean endsWith(String suffix) Tests if this string ends with the specified suffix. 10 boolean equals(Object anObject) Compares this string to the specified object. 11 boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations. 12 byte getBytes() Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array. 13 byte[] getBytes(String charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array. 14 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array. 15 int hashCode() Returns a hash code for this string. 16 int indexOf(int ch) Returns the index within this string of the first occurrence of the specified character. 17 int indexOf(int ch, int fromIndex)
- 32. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 32 Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index. 18 int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring. 19 int indexOf(String str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. 20 String intern() Returns a canonical representation for the string object. 21 int lastIndexOf(int ch) Returns the index within this string of the last occurrence of the specified character. 22 int lastIndexOf(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index. 23 int lastIndexOf(String str) Returns the index within this string of the rightmost occurrence of the specified substring. 24 int lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index. 25 int length() Returns the length of this string. 26 boolean matches(String regex) Tells whether or not this string matches the given regular expression. 27 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
- 33. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 33 Tests if two string regions are equal. 28 boolean regionMatches(int toffset, String other, int ooffset, int len) Tests if two string regions are equal. 29 String replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar. 30 String replaceAll(String regex, String replacement Replaces each substring of this string that matches the given regular expression with the given replacement. 31 String replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement. 32 String[] split(String regex) Splits this string around matches of the given regular expression. 33 String[] split(String regex, int limit) Splits this string around matches of the given regular expression. 34 boolean startsWith(String prefix) Tests if this string starts with the specified prefix. 35 boolean startsWith(String prefix, int toffset) Tests if this string starts with the specified prefix beginning a specified index. 36 CharSequence subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence. 37 String substring(int beginIndex) Returns a new string that is a substring of this string.
- 34. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 34 38 String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string. 39 char[] toCharArray() Converts this string to a new character array. 40 String toLowerCase() Converts all of the characters in this String to lower case using the rules of the default locale. 41 String toLowerCase(Locale locale) Converts all of the characters in this String to lower case using the rules of the given Locale. 42 String toString() This object (which is already a string!) is itself returned. 43 String toUpperCase() Converts all of the characters in this String to upper case using the rules of the default locale. 44 String toUpperCase(Locale locale) Converts all of the characters in this String to upper case using the rules of the given Locale. 45 String trim() Returns a copy of the string, with leading and trailing whitespace omitted. 46 static String valueOf(primitive data type x) Returns the string representation of the passed data type argument.
- 35. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 35 CONSTRUCTORS A constructor initializes an object when it is created. It has the same name as its class and is syntactically similar to a method. However, constructors have no explicit return type. Typically, you will use a constructor to give initial values to the instance variables defined by the class, or to perform any other start-up procedures required to create a fully formed object. All classes have constructors, whether you define one or not, because Java automatically provides a default constructor that initializes all member variables to zero. However, once you define your own constructor, the default constructor is no longer used. Syntax Following is the syntax of a constructor − class ClassName { ClassName() { } } Java allows two types of constructors namely − • No argument Constructors • Parameterized Constructors No argument Constructors As the name specifies the no argument constructors of Java does not accept any parameters instead, using these constructors the instance variables of a method will be initialized with fixed values for all objects. Example Public class MyClass { Int num; MyClass() { num = 100; } } You would call constructor to initialize objects as follows public class ConsDemo { public static void main(String args[]) { MyClass t1 = new MyClass(); MyClass t2 = new MyClass(); System.out.println(t1.num + " " + t2.num); }
- 36. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 36 } This would produce the following result 100 100 Parameterized Constructors Most often, you will need a constructor that accepts one or more parameters. Parameters are added to a constructor in the same way that they are added to a method, just declare them inside the parentheses after the constructor's name. Example Here is a simple example that uses a constructor − // A simple constructor. class MyClass { int x; // Following is the constructor MyClass(int i ) { x = i; } } You would call constructor to initialize objects as follows − public class ConsDemo { public static void main(String args[]) { MyClass t1 = new MyClass( 10 ); MyClass t2 = new MyClass( 20 ); System.out.println(t1.x + " " + t2.x); } } This would produce the following result − 10 20 JAVA OPERATORS Java provides a rich set of operators to manipulate variables. We can divide all the Java operators into the following groups − • Arithmetic Operators • Relational Operators • Bitwise Operators • Logical Operators • Assignment Operators
- 37. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 37 • Misc Operators The Arithmetic Operators Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators − Assume integer variable A holds 10 and variable B holds 20, then − Show Examples Operator Description Example + (Addition) Adds values on either side of the operator. A + B will give 30 - (Subtraction) Subtracts right-hand operand from left-hand operand. A - B will give -10 * (Multiplication) Multiplies values on either side of the operator. A * B will give 200 / (Division) Divides left-hand operand by right-hand operand. B / A will give 2 % (Modulus) Divides left-hand operand by right-hand operand and returns remainder. B % A will give 0 ++ (Increment) Increases the value of operand by 1. B++ gives 21 -- (Decrement) Decreases the value of operand by 1. B-- gives 19 The Relational Operators There are following relational operators supported by Java language. Assume variable A holds 10 and variable B holds 20, then − Show Examples
- 38. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 38 Operator Description Example == (equal to) Checks if the values of two operands are equal or not, if yes then condition becomes true. (A == B) is not true. != (not equal to) Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true. > (greater than) Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true. < (less than) Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true. >= (greater than or equal to) Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true. <= (less than or equal to) Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true. The Bitwise Operators Java defines several bitwise operators, which can be applied to the integer types, long, int, short, char, and byte. Bitwise operator works on bits and performs bit-by-bit operation. Assume if a = 60 and b = 13; now in binary format they will be as follows − a = 0011 1100 b = 0000 1101 ----------------- a&b = 0000 1100 a|b = 0011 1101 a^b = 0011 0001 ~a = 1100 0011 The following table lists the bitwise operators −
- 39. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 39 Assume integer variable A holds 60 and variable B holds 13 then − Show Examples Operator Description Example & (bitwise and) Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100 | (bitwise or) Binary OR Operator copies a bit if it exists in either operand. (A | B) will give 61 which is 0011 1101 ^ (bitwise XOR) Binary XOR Operator copies the bit if it is set in one operand but not both. (A ^ B) will give 49 which is 0011 0001 ~ (bitwise compliment) Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. (~A ) will give -61 which is 1100 0011 in 2's complement form due to a signed binary number. << (left shift) Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. A << 2 will give 240 which is 1111 0000 >> (right shift) Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is 1111 >>> (zero fill right shift) Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros. A >>>2 will give 15 which is 0000 1111 The Logical Operators The following table lists the logical operators − Assume Boolean variables A holds true and variable B holds false, then −
- 40. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 40 Show Examples Operator Description Example && (logical and) Called Logical AND operator. If both the operands are non-zero, then the condition becomes true. (A && B) is false || (logical or) Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true. (A || B) is true ! (logical not) Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false. !(A && B) is true The Assignment Operators Following are the assignment operators supported by Java language − Show Examples Operator Description Example = Simple assignment operator. Assigns values from right side operands to left side operand. C = A + B will assign value of A + B into C += Add AND assignment operator. It adds right operand to the left operand and assign the result to left operand. C += A is equivalent to C = C + A -= Subtract AND assignment operator. It subtracts right operand from the left operand and assign the result to left operand. C -= A is equivalent to C = C
- 41. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 41 – A *= Multiply AND assignment operator. It multiplies right operand with the left operand and assign the result to left operand. C *= A is equivalent to C = C * A /= Divide AND assignment operator. It divides left operand with the right operand and assign the result to left operand. C /= A is equivalent to C = C / A %= Modulus AND assignment operator. It takes modulus using two operands and assign the result to left operand. C %= A is equivalent to C = C % A <<= Left shift AND assignment operator. C <<= 2 is same as C = C << 2 >>= Right shift AND assignment operator. C >>= 2 is same as C = C >> 2 &= Bitwise AND assignment operator. C &= 2 is same as C = C & 2 ^= bitwise exclusive OR and assignment operator. C ^= 2 is same as C = C ^ 2
- 42. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 42 |= bitwise inclusive OR and assignment operator. C |= 2 is same as C = C | 2 Miscellaneous Operators There are few other operators supported by Java Language. Conditional Operator ( ? : ) Conditional operator is also known as the ternary operator. This operator consists of three operands and is used to evaluate Boolean expressions. The goal of the operator is to decide, which value should be assigned to the variable. The operator is written as − variable x = (expression) ? value if true : value if false Following is an example − Example public class Test { public static void main(String args[]) { int a, b; a = 10; b = (a == 1) ? 20: 30; System.out.println( "Value of b is : " + b ); b = (a == 10) ? 20: 30; System.out.println( "Value of b is : " + b ); } } This will produce the following result − Output Value of b is : 30 Value of b is : 20 instanceof Operator This operator is used only for object reference variables. The operator checks whether the object is of a particular type (class type or interface type). instanceof operator is written as − ( Object reference variable ) instanceof (class/interface type) If the object referred by the variable on the left side of the operator passes the IS-A check for the class/interface type on the right side, then the result will be true. Following is an example − Example
- 43. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 43 public class Test { public static void main(String args[]) { String name = "James"; // following will return true since name is type of String boolean result = name instanceof String; System.out.println( result ); } } This will produce the following result − Output true This operator will still return true, if the object being compared is the assignment compatible with the type on the right. Following is one more example − Example class Vehicle {} public class Car extends Vehicle { public static void main(String args[]) { Vehicle a = new Car(); boolean result = a instanceof Car; System.out.println( result ); } } This will produce the following result − Output true PRECEDENCE OF JAVA OPERATORS Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator − For example, x = 7 + 3 * 2; here x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3 * 2 and then adds into 7. Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
- 44. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 44 Category Operator Associativity Postfix expression++ expression-- Left to right Unary ++expression –-expression +expression –expression ~ ! Right to left Multiplicative * / % Left to right Additive + - Left to right Shift << >> >>> Left to right Relational < > <= >= instanceof Left to right Equality == != Left to right Bitwise AND & Left to right Bitwise XOR ^ Left to right Bitwise OR | Left to right Logical AND && Left to right Logical OR || Left to right Conditional ?: Right to left Assignment = += -= *= /= %= ^= |= <<= >>= >>>= Right to left
- 45. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 45 JAVA - LOOP CONTROL There may be a situation when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. Programming languages provide various control structures that allow for more complicated execution paths. A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages − Java programming language provides the following types of loop to handle looping requirements. Click the following links to check their detail. Sr.No. Loop & Description 1 while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body. 2 for loop Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable.
- 46. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 46 3 do...while loop Like a while statement, except that it tests the condition at the end of the loop body. Loop Control Statements Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Java supports the following control statements. Click the following links to check their detail. Sr.No. Control Statement & Description 1 break statement Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. 2 continue statement Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. Enhanced for loop in Java As of Java 5, the enhanced for loop was introduced. This is mainly used to traverse collection of elements including arrays. Syntax Following is the syntax of enhanced for loop − for(declaration : expression) { // Statements } • Declaration − The newly declared block variable, is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element. • Expression − This evaluates to the array you need to loop through. The expression can be an array variable or method call that returns an array. Example public class Test {
- 47. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 47 public static void main(String args[]) { int [] numbers = {10, 20, 30, 40, 50}; for(int x : numbers ) { System.out.print( x ); System.out.print(","); } System.out.print("n"); String [] names = {"James", "Larry", "Tom", "Lacy"}; for( String name : names ) { System.out.print( name ); System.out.print(","); } } } This will produce the following result − Output 10, 20, 30, 40, 50, James, Larry, Tom, Lacy, JAVA - DECISION MAKING Decision making structures have one or more conditions to be evaluated or tested by the program, along with a statement or statements that are to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false. Following is the general form of a typical decision making structure found in most of the programming languages −
- 48. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 48 Java programming language provides following types of decision making statements. Click the following links to check their detail. Sr.No. Statement & Description 1 if statement An if statement consists of a boolean expression followed by one or more statements. 2 if...else statement An if statement can be followed by an optional else statement, which executes when the boolean expression is false. 3 nested if statement You can use one if or else if statement inside another if or else if statement(s). 4 switch statement A switch statement allows a variable to be tested for equality against a list of values. The ? : Operator We have covered conditional operator ? : in the previous chapter which can be used to replace if...else statements. It has the following general form − Exp1 ? Exp2 : Exp3;
- 49. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 49 Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon. To determine the value of the whole expression, initially exp1 is evaluated. • If the value of exp1 is true, then the value of Exp2 will be the value of the whole expression. • If the value of exp1 is false, then Exp3 is evaluated and its value becomes the value of the entire expression. JAVA - NUMBERS CLASS Normally, when we work with Numbers, we use primitive data types such as byte, int, long, double, etc. Example int i = 5000; float gpa = 13.65; double mask = 0xaf; However, in development, we come across situations where we need to use objects instead of primitive data types. In order to achieve this, Java provides wrapper classes. All the wrapper classes (Integer, Long, Byte, Double, Float, Short) are subclasses of the abstract class Number. The object of the wrapper class contains or wraps its respective primitive data type. Converting primitive data types into object is called boxing, and this is taken care by the compiler. Therefore, while using a wrapper class you just need to pass the value of the primitive data type to the constructor of the Wrapper class. And the Wrapper object will be converted back to a primitive data type, and this process is called unboxing. The Number class is part of the java.lang package. Following is an example of boxing and unboxing − Example public class Test { public static void main(String args[]) { Integer x = 5; // boxes int to an Integer object x = x + 10; // unboxes the Integer to a int System.out.println(x);
- 50. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 50 } } This will produce the following result − Output 15 When x is assigned an integer value, the compiler boxes the integer because x is integer object. Later, x is unboxed so that they can be added as an integer. NUMBER METHODS Following is the list of the instance methods that all the subclasses of the Number class implements − Sr.No. Method & Description 1 xxxValue() Converts the value of this Number object to the xxx data type and returns it. 2 compareTo() Compares this Number object to the argument. 3 equals() Determines whether this number object is equal to the argument. 4 valueOf() Returns an Integer object holding the value of the specified primitive. 5 toString() Returns a String object representing the value of a specified int or Integer. 6 parseInt() This method is used to get the primitive data type of a certain String. 7 abs() Returns the absolute value of the argument.
- 51. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 51 8 ceil() Returns the smallest integer that is greater than or equal to the argument. Returned as a double. 9 floor() Returns the largest integer that is less than or equal to the argument. Returned as a double. 10 rint() Returns the integer that is closest in value to the argument. Returned as a double. 11 round() Returns the closest long or int, as indicated by the method's return type to the argument. 12 min() Returns the smaller of the two arguments. 13 max() Returns the larger of the two arguments. 14 exp() Returns the base of the natural logarithms, e, to the power of the argument. 15 log() Returns the natural logarithm of the argument. 16 pow() Returns the value of the first argument raised to the power of the second argument. 17 sqrt() Returns the square root of the argument. 18 sin() Returns the sine of the specified double value.
- 52. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 52 19 cos() Returns the cosine of the specified double value. 20 tan() Returns the tangent of the specified double value. 21 asin() Returns the arcsine of the specified double value. 22 acos() Returns the arccosine of the specified double value. 23 atan() Returns the arctangent of the specified double value. 24 atan2() Converts rectangular coordinates (x, y) to polar coordinate (r, theta) and returns theta. 25 toDegrees() Converts the argument to degrees. 26 toRadians() Converts the argument to radians. 27 random() Returns a random number. CHARACTER CLASS Normally, when we work with characters, we use primitive data types char. Example char ch = 'a';
- 53. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 53 // Unicode for uppercase Greek omega character char uniChar = 'u039A'; // an array of chars char[] charArray ={ 'a', 'b', 'c', 'd', 'e' }; However in development, we come across situations where we need to use objects instead of primitive data types. In order to achieve this, Java provides wrapper class Character for primitive data type char. The Character class offers a number of useful class (i.e., static) methods for manipulating characters. You can create a Character object with the Character constructor − Character ch = new Character('a'); The Java compiler will also create a Character object for you under some circumstances. For example, if you pass a primitive char into a method that expects an object, the compiler automatically converts the char to a Character for you. This feature is called autoboxing or unboxing, if the conversion goes the other way. Example // Here following primitive char 'a' // is boxed into the Character object ch Character ch = 'a'; // Here primitive 'x' is boxed for method test, // return is unboxed to char 'c' char c = test('x'); Escape Sequences A character preceded by a backslash () is an escape sequence and has a special meaning to the compiler. The newline character (n) has been used frequently in this page in System.out.println() statements to advance to the next line after the string is printed. Following table shows the Java escape sequences − Escape Sequence Description t Inserts a tab in the text at this point. b Inserts a backspace in the text at this point. n Inserts a newline in the text at this point.
- 54. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 54 r Inserts a carriage return in the text at this point. f Inserts a form feed in the text at this point. ' Inserts a single quote character in the text at this point. " Inserts a double quote character in the text at this point. Inserts a backslash character in the text at this point. When an escape sequence is encountered in a print statement, the compiler interprets it accordingly. Example If you want to put quotes within quotes, you must use the escape sequence, ", on the interior quotes − public class Test { public static void main(String args[]) { System.out.println("She said "Hello!" to me."); } } This will produce the following result − Output She said "Hello!" to me. CHARACTER METHODS Following is the list of the important instance methods that all the subclasses of the Character class implement Sr.No. Method & Description 1 isLetter() Determines whether the specified char value is a letter.
- 55. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 55 2 isDigit() Determines whether the specified char value is a digit. 3 isWhitespace() Determines whether the specified char value is white space. 4 isUpperCase() Determines whether the specified char value is uppercase. 5 isLowerCase() Determines whether the specified char value is lowercase. 6 toUpperCase() Returns the uppercase form of the specified char value. 7 toLowerCase() Returns the lowercase form of the specified char value. 8 toString() Returns a String object representing the specified character value that is, a one- character string. DATE AND TIME Java provides the Date class available in java.util package, this class encapsulates the current date and time. The Date class supports two constructors as shown in the following table. Sr.No. Constructor & Description 1 Date( ) This constructor initializes the object with the current date and time. 2 Date(long millisec)
- 56. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 56 This constructor accepts an argument that equals the number of milliseconds that have elapsed since midnight, January 1, 1970. Following are the methods of the date class. Sr.No. Method & Description 1 boolean after(Date date) Returns true if the invoking Date object contains a date that is later than the one specified by date, otherwise, it returns false. 2 boolean before(Date date) Returns true if the invoking Date object contains a date that is earlier than the one specified by date, otherwise, it returns false. 3 Object clone( ) Duplicates the invoking Date object. 4 int compareTo(Date date) Compares the value of the invoking object with that of date. Returns 0 if the values are equal. Returns a negative value if the invoking object is earlier than date. Returns a positive value if the invoking object is later than date. 5 int compareTo(Object obj) Operates identically to compareTo(Date) if obj is of class Date. Otherwise, it throws a ClassCastException. 6 boolean equals(Object date) Returns true if the invoking Date object contains the same time and date as the one specified by date, otherwise, it returns false. 7 long getTime( ) Returns the number of milliseconds that have elapsed since January 1, 1970. 8 int hashCode( )
- 57. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 57 Returns a hash code for the invoking object. 9 void setTime(long time) Sets the time and date as specified by time, which represents an elapsed time in milliseconds from midnight, January 1, 1970. 10 String toString( ) Converts the invoking Date object into a string and returns the result. Getting Current Date and Time This is a very easy method to get current date and time in Java. You can use a simple Date object with toString() method to print the current date and time as follows − Example import java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display time and date using toString() System.out.println(date.toString()); } } This will produce the following result − Output on May 04 09:51:52 CDT 2009 Date Comparison Following are the three ways to compare two dates − • You can use getTime( ) to obtain the number of milliseconds that have elapsed since midnight, January 1, 1970, for both objects and then compare these two values. • You can use the methods before( ), after( ), and equals( ). Because the 12th of the month comes before the 18th, for example, new Date(99, 2, 12).before(new Date (99, 2, 18)) returns true. • You can use the compareTo( ) method, which is defined by the Comparable interface and implemented by Date.
- 58. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 58 Date Formatting Using SimpleDateFormat SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting. Example import java.util.*; import java.text.*; public class DateDemo { public static void main(String args[]) { Date dNow = new Date( ); SimpleDateFormat ft = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz"); System.out.println("Current Date: " + ft.format(dNow)); } } This will produce the following result − Output Current Date: Sun 2004.07.18 at 04:14:09 PM PDT Simple DateFormat Format Codes To specify the time format, use a time pattern string. In this pattern, all ASCII letters are reserved as pattern letters, which are defined as the following − Character Description Example G Era designator AD y Year in four digits 2001 M Month in year July or 07 d Day in month 10
- 59. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 59 h Hour in A.M./P.M. (1~12) 12 H Hour in day (0~23) 22 m Minute in hour 30 s Second in minute 55 S Millisecond 234 E Day in week Tuesday D Day in year 360 F Day of week in month 2 (second Wed. in July) w Week in year 40 W Week in month 1 a A.M./P.M. marker PM k Hour in day (1~24) 24 K Hour in A.M./P.M. (0~11) 10 z Time zone Eastern Standard Time ' Escape for text Delimiter
- 60. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 60 " Single quote ` Date Formatting Using printf Date and time formatting can be done very easily using printf method. You use a two-letter format, starting with t and ending in one of the letters of the table as shown in the following code. Example import java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display time and date String str = String.format("Current Date/Time : %tc", date ); System.out.printf(str); } } This will produce the following result − Output Current Date/Time : Sat Dec 15 16:37:57 MST 2012 It would be a bit silly if you had to supply the date multiple times to format each part. For that reason, a format string can indicate the index of the argument to be formatted. The index must immediately follow the % and it must be terminated by a $. Example import java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display time and date System.out.printf("%1$s %2$tB %2$td, %2$tY", "Due date:", date); } } This will produce the following result −
- 61. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 61 Output Due date: February 09, 2004 Alternatively, you can use the < flag. It indicates that the same argument as in the preceding format specification should be used again. Example import java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display formatted date System.out.printf("%s %tB %<te, %<tY", "Due date:", date); } } This will produce the following result − Output Due date: February 09, 2004 Date and Time Conversion Characters Character Description Example c Complete date and time Mon May 04 09:51:52 CDT 2009 F ISO 8601 date 2004-02-09 D U.S. formatted date (month/day/year) 02/09/2004 T 24-hour time 18:05:19 r 12-hour time 06:05:19 pm R 24-hour time, no seconds 18:05
- 62. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 62 Y Four-digit year (with leading zeroes) 2004 y Last two digits of the year (with leading zeroes) 04 C First two digits of the year (with leading zeroes) 20 B Full month name February b Abbreviated month name Feb m Two-digit month (with leading zeroes) 02 d Two-digit day (with leading zeroes) 03 e Two-digit day (without leading zeroes) 9 A Full weekday name Monday a Abbreviated weekday name Mon j Three-digit day of year (with leading zeroes) 069 H Two-digit hour (with leading zeroes), between 00 and 23 18 k Two-digit hour (without leading zeroes), between 0 and 23 18 I Two-digit hour (with leading zeroes), between 01 and 12 06
- 63. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 63 l Two-digit hour (without leading zeroes), between 1 and 12 6 M Two-digit minutes (with leading zeroes) 05 S Two-digit seconds (with leading zeroes) 19 L Three-digit milliseconds (with leading zeroes) 047 N Nine-digit nanoseconds (with leading zeroes) 047000000 P Uppercase morning or afternoon marker PM p Lowercase morning or afternoon marker pm z RFC 822 numeric offset from GMT -0800 Z Time zone PST s Seconds since 1970-01-01 00:00:00 GMT 1078884319 Q Milliseconds since 1970-01-01 00:00:00 GMT 1078884319047 There are other useful classes related to Date and time. For more details, you can refer to Java Standard documentation. Parsing Strings into Dates The SimpleDateFormat class has some additional methods, notably parse( ), which tries to parse a string according to the format stored in the given SimpleDateFormat object. Example import java.util.*; import java.text.*;
- 64. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 64 public class DateDemo { public static void main(String args[]) { SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd"); String input = args.length == 0 ? "1818-11-11" : args[0]; System.out.print(input + " Parses as "); Date t; try { t = ft.parse(input); System.out.println(t); } catch (ParseException e) { System.out.println("Unparseable using " + ft); } } } A sample run of the above program would produce the following result − Output 1818-11-11 Parses as Wed Nov 11 00:00:00 EST 1818 Sleeping for a While You can sleep for any period of time from one millisecond up to the lifetime of your computer. For example, the following program would sleep for 3 seconds − Example import java.util.*; public class SleepDemo { public static void main(String args[]) { try { System.out.println(new Date( ) + "n"); Thread.sleep(5*60*10); System.out.println(new Date( ) + "n"); } catch (Exception e) { System.out.println("Got an exception!"); } } } This will produce the following result − Output Sun May 03 18:04:41 GMT 2009 Sun May 03 18:04:51 GMT 2009 Measuring Elapsed Time
- 65. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 65 Sometimes, you may need to measure point in time in milliseconds. So let's re-write the above example once again − Example import java.util.*; public class DiffDemo { public static void main(String args[]) { try { long start = System.currentTimeMillis( ); System.out.println(new Date( ) + "n"); Thread.sleep(5*60*10); System.out.println(new Date( ) + "n"); long end = System.currentTimeMillis( ); long diff = end - start; System.out.println("Difference is : " + diff); } catch (Exception e) { System.out.println("Got an exception!"); } } } This will produce the following result − Output Sun May 03 18:16:51 GMT 2009 Sun May 03 18:16:57 GMT 2009 Difference is : 5993 GregorianCalendar Class GregorianCalendar is a concrete implementation of a Calendar class that implements the normal Gregorian calendar with which you are familiar. We did not discuss Calendar class in this page, you can look up standard Java documentation for this. The getInstance( ) method of Calendar returns a GregorianCalendar initialized with the current date and time in the default locale and time zone. GregorianCalendar defines two fields: AD and BC. These represent the two eras defined by the Gregorian calendar. There are also several constructors for GregorianCalendar objects − Sr.No. Constructor & Description 1 GregorianCalendar() Constructs a default GregorianCalendar using the current time in the default time zone
- 66. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 66 with the default locale. 2 GregorianCalendar(int year, int month, int date) Constructs a GregorianCalendar with the given date set in the default time zone with the default locale. 3 GregorianCalendar(int year, int month, int date, int hour, int minute) Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale. 4 GregorianCalendar(int year, int month, int date, int hour, int minute, int second) Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale. 5 GregorianCalendar(Locale aLocale) Constructs a GregorianCalendar based on the current time in the default time zone with the given locale. 6 GregorianCalendar(TimeZone zone) Constructs a GregorianCalendar based on the current time in the given time zone with the default locale. 7 GregorianCalendar(TimeZone zone, Locale aLocale) Constructs a GregorianCalendar based on the current time in the given time zone with the given locale. Here is the list of few useful support methods provided by GregorianCalendar class − Sr.No. Method & Description 1 void add(int field, int amount) Adds the specified (signed) amount of time to the given time field, based on the calendar's rules. 2 protected void computeFields()
- 67. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 67 Converts UTC as milliseconds to time field values. 3 protected void computeTime() Overrides Calendar Converts time field values to UTC as milliseconds. 4 boolean equals(Object obj) Compares this GregorianCalendar to an object reference. 5 int get(int field) Gets the value for a given time field. 6 int getActualMaximum(int field) Returns the maximum value that this field could have, given the current date. 7 int getActualMinimum(int field) Returns the minimum value that this field could have, given the current date. 8 int getGreatestMinimum(int field) Returns highest minimum value for the given field if varies. 9 Date getGregorianChange() Gets the Gregorian Calendar change date. 10 int getLeastMaximum(int field) Returns lowest maximum value for the given field if varies. 11 int getMaximum(int field) Returns maximum value for the given field. 12 Date getTime() Gets this Calendar's current time.
- 68. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 68 13 long getTimeInMillis() Gets this Calendar's current time as a long. 14 TimeZone getTimeZone() Gets the time zone. 15 int getMinimum(int field) Returns minimum value for the given field. 16 int hashCode() Overrides hashCode. 17 boolean isLeapYear(int year) Determines if the given year is a leap year. 18 void roll(int field, boolean up) Adds or subtracts (up/down) a single unit of time on the given time field without changing larger fields. 19 void set(int field, int value) Sets the time field with the given value. 20 void set(int year, int month, int date) Sets the values for the fields year, month, and date. 21 void set(int year, int month, int date, int hour, int minute) Sets the values for the fields year, month, date, hour, and minute. 22 void set(int year, int month, int date, int hour, int minute, int second) Sets the values for the fields year, month, date, hour, minute, and second. 23 void setGregorianChange(Date date)
- 69. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 69 Sets the GregorianCalendar change date. 24 void setTime(Date date) Sets this Calendar's current time with the given Date. 25 void setTimeInMillis(long millis) Sets this Calendar's current time from the given long value. 26 void setTimeZone(TimeZone value) Sets the time zone with the given time zone value. 27 String toString() Returns a string representation of this calendar. Example import java.util.*; public class GregorianCalendarDemo { public static void main(String args[]) { String months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"}; int year; // Create a Gregorian calendar initialized // with the current date and time in the // default locale and timezone. GregorianCalendar gcalendar = new GregorianCalendar(); // Display current time and date information. System.out.print("Date: "); System.out.print(months[gcalendar.get(Calendar.MONTH)]); System.out.print(" " + gcalendar.get(Calendar.DATE) + " "); System.out.println(year = gcalendar.get(Calendar.YEAR)); System.out.print("Time: "); System.out.print(gcalendar.get(Calendar.HOUR) + ":"); System.out.print(gcalendar.get(Calendar.MINUTE) + ":"); System.out.println(gcalendar.get(Calendar.SECOND)); // Test if the current year is a leap year if(gcalendar.isLeapYear(year)) {
- 70. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 70 System.out.println("The current year is a leap year"); }else { System.out.println("The current year is not a leap year"); } } } This will produce the following result − Output Date: Apr 22 2009 Time: 11:25:27 The current year is not a leap year METHODS A Java method is a collection of statements that are grouped together to perform an operation. When you call the System.out.println() method, for example, the system actually executes several statements in order to display a message on the console. Now you will learn how to create your own methods with or without return values, invoke a method with or without parameters, and apply method abstraction in the program design. Creating Method Considering the following example to explain the syntax of a method − Syntax public static int methodName(int a, int b) { // body } Here, • public static − modifier • int − return type • methodName − name of the method • a, b − formal parameters • int a, int b − list of parameters Method definition consists of a method header and a method body. The same is shown in the following syntax − Syntax modifier returnType nameOfMethod (Parameter List) { // method body } The syntax shown above includes − • modifier − It defines the access type of the method and it is optional to use.
- 71. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 71 • returnType − Method may return a value. • nameOfMethod − This is the method name. The method signature consists of the method name and the parameter list. • Parameter List − The list of parameters, it is the type, order, and number of parameters of a method. These are optional, method may contain zero parameters. • method body − The method body defines what the method does with the statements. Example Here is the source code of the above defined method called min(). This method takes two parameters num1 and num2 and returns the maximum between the two − /** the snippet returns the minimum between two numbers */ public static int minFunction(int n1, int n2) { int min; if (n1 > n2) min = n2; else min = n1; return min; } Method Calling For using a method, it should be called. There are two ways in which a method is called i.e., method returns a value or returning nothing (no return value). The process of method calling is simple. When a program invokes a method, the program control gets transferred to the called method. This called method then returns control to the caller in two conditions, when − • the return statement is executed. • it reaches the method ending closing brace. The methods returning void is considered as call to a statement. Lets consider an example − System.out.println("This is pagespoint.com!"); The method returning value can be understood by the following example − int result = sum(6, 9); Following is the example to demonstrate how to define a method and how to call it − Example public class ExampleMinNumber { public static void main(String[] args) {
- 72. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 72 int a = 11; int b = 6; int c = minFunction(a, b); System.out.println("Minimum Value = " + c); } /** returns the minimum of two numbers */ public static int minFunction(int n1, int n2) { int min; if (n1 > n2) min = n2; else min = n1; return min; } } This will produce the following result − Output Minimum value = 6 The void Keyword The void keyword allows us to create methods which do not return a value. Here, in the following example we're considering a void method methodRankPoints. This method is a void method, which does not return any value. Call to a void method must be a statement i.e. methodRankPoints(255.7);. It is a Java statement which ends with a semicolon as shown in the following example. Example public class ExampleVoid { public static void main(String[] args) { methodRankPoints(255.7); } public static void methodRankPoints(double points) { if (points >= 202.5) { System.out.println("Rank:A1"); }else if (points >= 122.4) { System.out.println("Rank:A2"); }else { System.out.println("Rank:A3"); } } }
- 73. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 73 This will produce the following result − Output Rank:A1 Passing Parameters by Value While working under calling process, arguments is to be passed. These should be in the same order as their respective parameters in the method specification. Parameters can be passed by value or by reference. Passing Parameters by Value means calling a method with a parameter. Through this, the argument value is passed to the parameter. Example The following program shows an example of passing parameter by value. The values of the arguments remains the same even after the method invocation. public class swappingExample { public static void main(String[] args) { int a = 30; int b = 45; System.out.println("Before swapping, a = " + a + " and b = " + b); // Invoke the swap method swapFunction(a, b); System.out.println("n**Now, Before and After swapping values will be same here**:"); System.out.println("After swapping, a = " + a + " and b is " + b); } public static void swapFunction(int a, int b) { System.out.println("Before swapping(Inside), a = " + a + " b = " + b); // Swap n1 with n2 int c = a; a = b; b = c; System.out.println("After swapping(Inside), a = " + a + " b = " + b); } } This will produce the following result − Output Before swapping, a = 30 and b = 45 Before swapping(Inside), a = 30 b = 45 After swapping(Inside), a = 45 b = 30
- 74. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 74 **Now, Before and After swapping values will be same here**: After swapping, a = 30 and b is 45 METHOD OVERLOADING When a class has two or more methods by the same name but different parameters, it is known as method overloading. It is different from overriding. In overriding, a method has the same method name, type, number of parameters, etc. Let’s consider the example discussed earlier for finding minimum numbers of integer type. If, let’s say we want to find the minimum number of double type. Then the concept of overloading will be introduced to create two or more methods with the same name but different parameters. The following example explains the same − Example public class ExampleOverloading { public static void main(String[] args) { int a = 11; int b = 6; double c = 7.3; double d = 9.4; int result1 = minFunction(a, b); // same function name with different parameters double result2 = minFunction(c, d); System.out.println("Minimum Value = " + result1); System.out.println("Minimum Value = " + result2); } // for integer public static int minFunction(int n1, int n2) { int min; if (n1 > n2) min = n2; else min = n1; return min; } // for double public static double minFunction(double n1, double n2) { double min; if (n1 > n2) min = n2; else
- 75. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 75 min = n1; return min; } } This will produce the following result − Output Minimum Value = 6 Minimum Value = 7.3 Overloading methods makes program readable. Here, two methods are given by the same name but with different parameters. The minimum number from integer and double types is the result. Using Command-Line Arguments Sometimes you will want to pass some information into a program when you run it. This is accomplished by passing command-line arguments to main( ). A command-line argument is the information that directly follows the program's name on the command line when it is executed. To access the command-line arguments inside a Java program is quite easy. They are stored as strings in the String array passed to main( ). Example The following program displays all of the command-line arguments that it is called with − public class CommandLine { public static void main(String args[]) { for(int i = 0; i<args.length; i++) { System.out.println("args[" + i + "]: " + args[i]); } } } Try executing this program as shown here − $java CommandLine this is a command line 200 -100 This will produce the following result − Output args[0]: this args[1]: is args[2]: a args[3]: command args[4]: line args[5]: 200 args[6]: -100
- 76. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 76 THE THIS KEYWORD this is a keyword in Java which is used as a reference to the object of the current class, with in an instance method or a constructor. Using this you can refer the members of a class such as constructors, variables and methods. Note − The keyword this is used only within instance methods or constructors In general, the keyword this is used to − • Differentiate the instance variables from local variables if they have same names, within a constructor or a method. class Student { int age; Student(int age) { this.age = age; } } • Call one type of constructor (parametrized constructor or default) from other in a class. It is known as explicit constructor invocation. class Student { int age Student() { this(20); } Student(int age) { this.age = age; } } Example Here is an example that uses this keyword to access the members of a class. Copy and paste the following program in a file with the name, This_Example.java. public class This_Example { // Instance variable num int num = 10;
- 77. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 77 This_Example() { System.out.println("This is an example program on keyword this"); } This_Example(int num) { // Invoking the default constructor this(); // Assigning the local variable num to the instance variable num this.num = num; } public void greet() { System.out.println("Hi Welcome to Pagespoint"); } public void print() { // Local variable num int num = 20; // Printing the local variable System.out.println("value of local variable num is : "+num); // Printing the instance variable System.out.println("value of instance variable num is : "+this.num); // Invoking the greet method of a class this.greet(); } public static void main(String[] args) { // Instantiating the class This_Example obj1 = new This_Example(); // Invoking the print method obj1.print(); // Passing a new value to the num variable through parametrized constructor This_Example obj2 = new This_Example(30); // Invoking the print method again obj2.print(); } } This will produce the following result − Output This is an example program on keyword this
- 78. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 78 value of local variable num is : 20 value of instance variable num is : 10 Hi Welcome to Pagespoint This is an example program on keyword this value of local variable num is : 20 value of instance variable num is : 30 Hi Welcome to Pagespoint Variable Arguments(var-args) JDK 1.5 enables you to pass a variable number of arguments of the same type to a method. The parameter in the method is declared as follows − typeName... parameterName In the method declaration, you specify the type followed by an ellipsis (...). Only one variable-length parameter may be specified in a method, and this parameter must be the last parameter. Any regular parameters must precede it. Example public class VarargsDemo { public static void main(String args[]) { // Call method with variable args printMax(34, 3, 3, 2, 56.5); printMax(new double[]{1, 2, 3}); } public static void printMax( double... numbers) { if (numbers.length == 0) { System.out.println("No argument passed"); return; } double result = numbers[0]; for (int i = 1; i < numbers.length; i++) if (numbers[i] > result) result = numbers[i]; System.out.println("The max value is " + result); } } This will produce the following result − Output The max value is 56.5 The max value is 3.0 The finalize( ) Method
- 79. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 79 It is possible to define a method that will be called just before an object's final destruction by the garbage collector. This method is called finalize( ), and it can be used to ensure that an object terminates cleanly. For example, you might use finalize( ) to make sure that an open file owned by that object is closed. To add a finalizer to a class, you simply define the finalize( ) method. The Java runtime calls that method whenever it is about to recycle an object of that class. Inside the finalize( ) method, you will specify those actions that must be performed before an object is destroyed. The finalize( ) method has this general form − protected void finalize( ) { // finalization code here } Here, the keyword protected is a specifier that prevents access to finalize( ) by code defined outside its class. This means that you cannot know when or even if finalize( ) will be executed. For example, if your program ends before garbage collection occurs, finalize( ) will not execute. PACKAGES Packages are used in Java in order to prevent naming conflicts, to control access, to make searching/locating and usage of classes, interfaces, enumerations and annotations easier, etc. A Package can be defined as a grouping of related types (classes, interfaces, enumerations and annotations ) providing access protection and namespace management. Some of the existing packages in Java are − • java.lang − bundles the fundamental classes • java.io − classes for input , output functions are bundled in this package Programmers can define their own packages to bundle group of classes/interfaces, etc. It is a good practice to group related classes implemented by you so that a programmer can easily determine that the classes, interfaces, enumerations, and annotations are related. Since the package creates a new namespace there won't be any name conflicts with names in other packages. Using packages, it is easier to provide access control and it is also easier to locate the related classes. Creating a Package While creating a package, you should choose a name for the package and include a package statement along with that name at the top of every source file that contains the classes, interfaces, enumerations, and annotation types that you want to include in the package. The package statement should be the first line in the source file. There can be only one package statement in each source file, and it applies to all types in the file.
- 80. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 80 If a package statement is not used then the class, interfaces, enumerations, and annotation types will be placed in the current default package. To compile the Java programs with package statements, you have to use -d option as shown below. javac -d Destination_folder file_name.java Then a folder with the given package name is created in the specified destination, and the compiled class files will be placed in that folder. Example Let us look at an example that creates a package called animals. It is a good practice to use names of packages with lower case letters to avoid any conflicts with the names of classes and interfaces. Following package example contains interface named animals − /* File name : Animal.java */ package animals; interface Animal { public void eat(); public void travel(); } Now, let us implement the above interface in the same package animals − package animals; /* File name : MammalInt.java */ public class MammalInt implements Animal { public void eat() { System.out.println("Mammal eats"); } public void travel() { System.out.println("Mammal travels"); } public int noOfLegs() { return 0; } public static void main(String args[]) { MammalInt m = new MammalInt(); m.eat(); m.travel(); } }
- 81. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 81 Now compile the java files as shown below − $ javac -d . Animal.java $ javac -d . MammalInt.java Now a package/folder with the name animals will be created in the current directory and these class files will be placed in it as shown below. You can execute the class file within the package and get the result as shown below. Mammal eats Mammal travels The import Keyword If a class wants to use another class in the same package, the package name need not be used. Classes in the same package find each other without any special syntax. Example Here, a class named Boss is added to the payroll package that already contains Employee. The Boss can then refer to the Employee class without using the payroll prefix, as demonstrated by the following Boss class. package payroll; public class Boss { public void payEmployee(Employee e) { e.mailCheck(); } } What happens if the Employee class is not in the payroll package? The Boss class must then use one of the following techniques for referring to a class in a different package. • The fully qualified name of the class can be used. For example −
- 82. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 82 payroll.Employee • The package can be imported using the import keyword and the wild card (*). For example − import payroll.*; • The class itself can be imported using the import keyword. For example − import payroll.Employee; Note − A class file can contain any number of import statements. The import statements must appear after the package statement and before the class declaration. The Directory Structure of Packages Two major results occur when a class is placed in a package − • The name of the package becomes a part of the name of the class, as we just discussed in the previous section. • The name of the package must match the directory structure where the corresponding bytecode resides. Here is simple way of managing your files in Java − Put the source code for a class, interface, enumeration, or annotation type in a text file whose name is the simple name of the type and whose extension is .java. For example − // File Name : Car.java package vehicle; public class Car { // Class implementation. } Now, put the source file in a directory whose name reflects the name of the package to which the class belongs − ....vehicleCar.java Now, the qualified class name and pathname would be as follows − • Class name → vehicle.Car • Path name → vehicleCar.java (in windows) In general, a company uses its reversed Internet domain name for its package names. Example − A company's Internet domain name is apple.com, then all its package names would start with com.apple. Each component of the package name corresponds to a subdirectory.
- 83. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 83 Example − The company had a com.apple.computers package that contained a Dell.java source file, it would be contained in a series of subdirectories like this − ....comapplecomputersDell.java At the time of compilation, the compiler creates a different output file for each class, interface and enumeration defined in it. The base name of the output file is the name of the type, and its extension is .class. For example − // File Name: Dell.java package com.apple.computers; public class Dell { } class Ups { } Now, compile this file as follows using -d option − $javac -d . Dell.java The files will be compiled as follows − .comapplecomputersDell.class .comapplecomputersUps.class You can import all the classes or interfaces defined in comapplecomputers as follows − import com.apple.computers.*; Like the .java source files, the compiled .class files should be in a series of directories that reflect the package name. However, the path to the .class files does not have to be the same as the path to the .java source files. You can arrange your source and class directories separately, as − <path-one>sourcescomapplecomputersDell.java <path-two>classescomapplecomputersDell.class By doing this, it is possible to give access to the classes directory to other programmers without revealing your sources. You also need to manage source and class files in this manner so that the compiler and the Java Virtual Machine (JVM) can find all the types your program uses. The full path to the classes directory, <path-two>classes, is called the class path, and is set with the CLASSPATH system variable. Both the compiler and the JVM construct the path to your .class files by adding the package name to the class path. Say <path-two>classes is the class path, and the package name is com.apple.computers, then the compiler and JVM will look for .class files in <path- two>classescomapplecomputers.
- 84. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 84 A class path may include several paths. Multiple paths should be separated by a semicolon (Windows) or colon (Unix). By default, the compiler and the JVM search the current directory and the JAR file containing the Java platform classes so that these directories are automatically in the class path. Set CLASSPATH System Variable To display the current CLASSPATH variable, use the following commands in Windows and UNIX (Bourne shell) − • In Windows → C:> set CLASSPATH • In UNIX → % echo $CLASSPATH To delete the current contents of the CLASSPATH variable, use − • In Windows → C:> set CLASSPATH = • In UNIX → % unset CLASSPATH; export CLASSPATH To set the CLASSPATH variable − • In Windows → set CLASSPATH = C:usersjackjavaclasses • In UNIX → % CLASSPATH = /home/jack/java/classes; export CLASSPATH STATIC CLASS The static keyword in Java is used for memory management mainly. We can apply static keyword with variables, methods, blocks and nested classes. The static keyword belongs to the class than an instance of the class. The static can be: 1. Variable (also known as a class variable) 2. Method (also known as a class method) 3. Block 4. Nested class
- 85. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 85 1) Java static variable If you declare any variable as static, it is known as a static variable. o The static variable can be used to refer to the common property of all objects (which is not unique for each object), for example, the company name of employees, college name of students, etc. o The static variable gets memory only once in the class area at the time of class loading. Advantages of static variable It makes your program memory efficient (i.e., it saves memory). Understanding the problem without static variable 1. class Student{ 2. int rollno; 3. String name; 4. String college="ITS"; 5. } Suppose there are 500 students in my college, now all instance data members will get memory each time when the object is created. All students have its unique rollno and name, so instance data member is good in such case. Here, "college" refers to the common property of all objects. If we make it static, this field will get the memory only once.
- 86. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 86 Example of static variable 1. //Java Program to demonstrate the use of static variable 2. class Student{ 3. int rollno;//instance variable 4. String name; 5. static String college ="ITS";//static variable 6. //constructor 7. Student(int r, String n){ 8. rollno = r; 9. name = n; 10. } 11. //method to display the values 12. void display (){System.out.println(rollno+" "+name+" "+college);} 13. } 14. //Test class to show the values of objects 15. public class TestStaticVariable1{ 16. public static void main(String args[]){ 17. Student s1 = new Student(111,"Karan"); 18. Student s2 = new Student(222,"Aryan"); 19. //we can change the college of all objects by the single line of code 20. //Student.college="BBDIT"; 21. s1.display(); 22. s2.display(); 23. } 24. } Output: 111 Karan ITS 222 Aryan ITS Program of the counter without static variable In this example, we have created an instance variable named count which is incremented in the constructor. Since instance variable gets the memory at the time of object creation, each object will have the copy of the instance variable. If it is incremented, it won't reflect other objects. So each object will have the value 1 in the count variable. 1. //Java Program to demonstrate the use of an instance variable 2. //which get memory each time when we create an object of the class. 3. class Counter{ 4. int count=0;//will get memory each time when the instance is created 5. 6. Counter(){
- 87. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 87 7. count++;//incrementing value 8. System.out.println(count); 9. } 10. 11. public static void main(String args[]){ 12. //Creating objects 13. Counter c1=new Counter(); 14. Counter c2=new Counter(); 15. Counter c3=new Counter(); 16. } 17. } Output: 1 1 1 Program of counter by static variable As we have mentioned above, static variable will get the memory only once, if any object changes the value of the static variable, it will retain its value. 1. //Java Program to illustrate the use of static variable which 2. //is shared with all objects. 3. class Counter2{ 4. static int count=0;//will get memory only once and retain its value 5. 6. Counter2(){ 7. count++;//incrementing the value of static variable 8. System.out.println(count); 9. } 10. 11. public static void main(String args[]){ 12. //creating objects 13. Counter2 c1=new Counter2(); 14. Counter2 c2=new Counter2(); 15. Counter2 c3=new Counter2(); 16. } 17. } Output:
- 88. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 88 1 2 3 2) Java static method If you apply static keyword with any method, it is known as static method. o A static method belongs to the class rather than the object of a class. o A static method can be invoked without the need for creating an instance of a class. o A static method can access static data member and can change the value of it. Example of static method 1. //Java Program to demonstrate the use of a static method. 2. class Student{ 3. int rollno; 4. String name; 5. static String college = "ITS"; 6. //static method to change the value of static variable 7. static void change(){ 8. college = "BBDIT"; 9. } 10. //constructor to initialize the variable 11. Student(int r, String n){ 12. rollno = r; 13. name = n; 14. } 15. //method to display values 16. void display(){System.out.println(rollno+" "+name+" "+college);} 17. } 18. //Test class to create and display the values of object 19. public class TestStaticMethod{ 20. public static void main(String args[]){ 21. Student.change();//calling change method 22. //creating objects 23. Student s1 = new Student(111,"Karan"); 24. Student s2 = new Student(222,"Aryan"); 25. Student s3 = new Student(333,"Sonoo"); 26. //calling display method 27. s1.display(); 28. s2.display(); 29. s3.display(); 30. }
- 89. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 89 31. } Output:111 Karan BBDIT 222 Aryan BBDIT 333 Sonoo BBDIT Another example of a static method that performs a normal calculation 1. //Java Program to get the cube of a given number using the static method 2. 3. class Calculate{ 4. static int cube(int x){ 5. return x*x*x; 6. } 7. 8. public static void main(String args[]){ 9. int result=Calculate.cube(5); 10. System.out.println(result); 11. } 12. } Output:125 Restrictions for the static method There are two main restrictions for the static method. They are: 1. The static method can not use non static data member or call non-static method directly. 2. this and super cannot be used in static context. 1. class A{ 2. int a=40;//non static 3. 4. public static void main(String args[]){ 5. System.out.println(a); 6. } 7. } Output:Compile Time Error Q) Why is the Java main method static? Ans) It is because the object is not required to call a static method. If it were a non-static method, JVM creates an object first then call main() method that will lead the problem of extra memory allocation.
- 90. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 90 3) Java static block o Is used to initialize the static data member. o It is executed before the main method at the time of classloading. Example of static block 1. class A2{ 2. static{System.out.println("static block is invoked");} 3. public static void main(String args[]){ 4. System.out.println("Hello main"); 5. } 6. } Output:static block is invoked Hello main Q) Can we execute a program without main() method? Ans) No, one of the ways was the static block, but it was possible till JDK 1.6. Since JDK 1.7, it is not possible to execute a Java class without the main method. 1. class A3{ 2. static{ 3. System.out.println("static block is invoked"); 4. System.exit(0); 5. } 6. } Output: static block is invoked Since JDK 1.7 and above, output would be: Error: Main method not found in class A3, please define the main method as: public static void main(String[] args) or a JavaFX application class must extend javafx.application.Application METHOD OVERLOADING In Java, two or more methods can have same name if they differ in parameters (different number of parameters, different types of parameters, or both). These methods are called overloaded methods and this feature is called method overloading. For example:
- 91. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 91 void func() { ... } void func(int a) { ... } float func(double a) { ... } float func(int a, float b) { ... } Here, the func() method is overloaded. These methods have the same name but accept different arguments. Notice that, the return type of these methods is not the same. Overloaded methods may or may not have different return types, but they must differ in parameters they accept. Why method overloading? Suppose, you have to perform the addition of given numbers but there can be any number of arguments (let’s say either 2 or 3 arguments for simplicity). In order to accomplish the task, you can create two methods sum2num(int, int) and sum3num(int, int, int) for two and three parameters respectively. However, other programmers, as well as you in the future may get confused as the behavior of both methods are the same but they differ by name. The better way to accomplish this task is by overloading methods. And, depending upon the argument passed, one of the overloaded methods is called. This helps to increase the readability of the program. How to perform method overloading in Java? Here are different ways to perform method overloading: 1. Overloading by changing the number of arguments class MethodOverloading { private static void display(int a){ System.out.println("Arguments: " + a); }
- 92. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 92 private static void display(int a, int b){ System.out.println("Arguments: " + a + " and " + b); } public static void main(String[] args) { display(1); display(1, 4); } } Output: Arguments: 1 Arguments: 1 and 4 2. By changing the datatype of parameters class MethodOverloading { // this method accepts int private static void display(int a){ System.out.println("Got Integer data."); } // this method accepts String object private static void display(String a){ System.out.println("Got String object."); } public static void main(String[] args) { display(1); display("Hello"); } } Output: Got Integer data. Got String object. Here, both overloaded methods accept one argument. However, one accepts the argument of type int whereas other accepts String object. Let’s look at a real-world example:
- 93. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 93 class HelperService { private String formatNumber(int value) { return String.format("%d", value); } private String formatNumber(double value) { return String.format("%.3f", value); } private String formatNumber(String value) { return String.format("%.2f", Double.parseDouble(value)); } public static void main(String[] args) { HelperService hs = new HelperService(); System.out.println(hs.formatNumber(500)); System.out.println(hs.formatNumber(89.9934)); System.out.println(hs.formatNumber("550")); } } When you run the program, the output will be: 500 89.993 550.00 Note: In Java, you can also overload constructors in a similar way like methods. Recommended Reading: Java Constructor Overloading Important Points • Two or more methods can have same name inside the same class if they accept different arguments. This feature is known as method overloading. • Method overloading is achieved by either: o changing the number of arguments. o or changing the datatype of arguments.
- 94. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 94 • Method overloading is not possible by changing the return type of methods. JAVA ENUMS The Enum in Java is a data type which contains a fixed set of constants. It can be used for days of the week (SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY) , directions (NORTH, SOUTH, EAST, and WEST), season (SPRING, SUMMER, WINTER, and AUTUMN or FALL), colors (RED, YELLOW, BLUE, GREEN, WHITE, and BLACK) etc. According to the Java naming conventions, we should have all constants in capital letters. So, we have enum constants in capital letters. Java Enums can be thought of as classes which have a fixed set of constants (a variable that does not change). The Java enum constants are static and final implicitly. It is available since JDK 1.5. Enums are used to create our own data type like classes. The enum data type (also known as Enumerated Data Type) is used to define an enum in Java. Unlike C/C++, enum in Java is more powerful. Here, we can define an enum either inside the class or outside the class. Java Enum internally inherits the Enum class, so it cannot inherit any other class, but it can implement many interfaces. We can have fields, constructors, methods, and main methods in Java enum. Points to remember for Java Enum o Enum improves type safety o Enum can be easily used in switch o Enum can be traversed o Enum can have fields, constructors and methods o Enum may implement many interfaces but cannot extend any class because it internally extends Enum class
- 95. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 95 Simple Example of Java Enum 1. class EnumExample1{ 2. //defining the enum inside the class 3. public enum Season { WINTER, SPRING, SUMMER, FALL } 4. //main method 5. public static void main(String[] args) { 6. //traversing the enum 7. for (Season s : Season.values()) 8. System.out.println(s); 9. }} Output: WINTER SPRING SUMMER FALL Let us see another example of Java enum where we are using value(), valueOf(), and ordinal() methods of Java enum.
- 96. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 96 1. class EnumExample1{ 2. //defining enum within class 3. public enum Season { WINTER, SPRING, SUMMER, FALL } 4. //creating the main method 5. public static void main(String[] args) { 6. //printing all enum 7. for (Season s : Season.values()){ 8. System.out.println(s); 9. } 10. System.out.println("Value of WINTER is: "+Season.valueOf("WINTER")); 11. System.out.println("Index of WINTER is: "+Season.valueOf("WINTER").ordinal()); 12. System.out.println("Index of SUMMER is: "+Season.valueOf("SUMMER").ordinal()); 13. 14. }} Output: WINTER SPRING SUMMER FALL Value of WINTER is: WINTER Index of WINTER is: 0 Index of SUMMER is: 2 Note: Java compiler internally adds values(), valueOf() and ordinal() methods within the enum at compile time. It internally creates a static and final class for the enum. What is the purpose of the values() method in the enum? The Java compiler internally adds the values() method when it creates an enum. The values() method returns an array containing all the values of the enum. What is the purpose of the valueOf() method in the enum? The Java compiler internally adds the valueOf() method when it creates an enum. The valueOf() method returns the value of given constant enum. What is the purpose of the ordinal() method in the enum? The Java compiler internally adds the ordinal() method when it creates an enum. The ordinal() method returns the index of the enum value.
- 97. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 97 Defining Java Enum The enum can be defined within or outside the class because it is similar to a class. The semicolon (;) at the end of the enum constants are optional. For example: 1. enum Season { WINTER, SPRING, SUMMER, FALL } Or, 1. enum Season { WINTER, SPRING, SUMMER, FALL; } Both the definitions of Java enum are the same. Java Enum Example: Defined outside class 1. enum Season { WINTER, SPRING, SUMMER, FALL } 2. class EnumExample2{ 3. public static void main(String[] args) { 4. Season s=Season.WINTER; 5. System.out.println(s); 6. }} Output: WINTER Java Enum Example: Defined inside class 1. class EnumExample3{ 2. enum Season { WINTER, SPRING, SUMMER, FALL; }//semicolon(;) is optional here 3. public static void main(String[] args) { 4. Season s=Season.WINTER;//enum type is required to access WINTER 5. System.out.println(s); 6. }} Output: WINTER Java Enum Example: main method inside Enum If you put main() method inside the enum, you can run the enum directly. 1. enum Season { 2. WINTER, SPRING, SUMMER, FALL; 3. public static void main(String[] args) { 4. Season s=Season.WINTER; 5. System.out.println(s);
- 98. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 98 6. } 7. } Output: WINTER Initializing specific values to the enum constants The enum constants have an initial value which starts from 0, 1, 2, 3, and so on. But, we can initialize the specific value to the enum constants by defining fields and constructors. As specified earlier, Enum can have fields, constructors, and methods. Example of specifying initial value to the enum constants 1. class EnumExample4{ 2. enum Season{ 3. WINTER(5), SPRING(10), SUMMER(15), FALL(20); 4. 5. private int value; 6. private Season(int value){ 7. this.value=value; 8. } 9. } 10. public static void main(String args[]){ 11. for (Season s : Season.values()) 12. System.out.println(s+" "+s.value); 13. 14. }} 15. Output: WINTER 5 SPRING 10 SUMMER 15 FALL 20 1. enum Season{ 2. WINTER(10),SUMMER(20); 3. private int value; 4. Season(int value){ 5. this.value=value; 6. }
- 99. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 99 7. } Internal code generated by the compiler for the above example of enum type 1. final class Season extends Enum 2. { 3. public static Season[] values() 4. { 5. return (Season[])$VALUES.clone(); 6. } 7. public static Season valueOf(String s) 8. { 9. return (Season)Enum.valueOf(Season, s); 10. } 11. private Season(String s, int i, int j) 12. { 13. super(s, i); 14. value = j; 15. } 16. public static final Season WINTER; 17. public static final Season SUMMER; 18. private int value; 19. private static final Season $VALUES[]; 20. static 21. { 22. WINTER = new Season("WINTER", 0, 10); 23. SUMMER = new Season("SUMMER", 1, 20); 24. $VALUES = (new Season[] { 25. WINTER, SUMMER 26. }); 27. } 28. } Java Enum in a switch statement We can apply enum on switch statement as in the given example: Example of applying Enum on a switch statement 1. class EnumExample5{ 2. enum Day{ SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, S ATURDAY} 3. public static void main(String args[]){ 4. Day day=Day.MONDAY;
- 100. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 100 5. 6. switch(day){ 7. case SUNDAY: 8. System.out.println("sunday"); 9. break; 10. case MONDAY: 11. System.out.println("monday"); 12. break; 13. default: 14. System.out.println("other day"); 15. } 16. }} Output: monday JAVA GARBAGE COLLECTION In java, garbage means unreferenced objects. Garbage Collection is process of reclaiming the runtime unused memory automatically. In other words, it is a way to destroy the unused objects. To do so, we were using free() function in C language and delete() in C++. But, in java it is performed automatically. So, java provides better memory management. Advantage of Garbage Collection o It makes java memory efficient because garbage collector removes the unreferenced objects from heap memory. o It is automatically done by the garbage collector(a part of JVM) so we don't need to make extra efforts. How can an object be unreferenced? There are many ways: o By nulling the reference o By assigning a reference to another o By anonymous object etc.
- 101. SHANMUGA INDUSTRIES ARTS AND SCIENCE COLLEGE, TIRUVANNAMALAI-606603. PROGRAMMING IN JAVA A. SIVASANKARI, ASSISTANT PROFESSOR, DEPT OF COMPUTER APPLICATION 101