Java Presentation For Syntax

What is Java Technology?
Java technology is:
A programming language
●
–
A development environment
An application environment
–
–
It is similar in syntax to C++.
It is used for developing both applets
●
and applications.●
Thanks to its scalable nature, Java has emerged as the most preferred language
in Web and Mobile application development

Primary Goals of the
Java Technology
Provides an easy-to-use language by:
Avoiding many pitfalls of other languages
●
–
Being object-oriented
Enabling users to create streamlined and clear code
–
–
Provides an interpreted environment for:Provides an interpreted environment for:
Improved speed of development
●
–
Code portability–

Java Technology
Enables users to run more than one thread of activity
Loads classes dynamically; that is, at the time they are actually
needed
Supports changing programs dynamically during runtime by loading
classes from disparate sources
●
●
●
classes from disparate sources
Furnishes better security●

Java Technology
The following features fulfill these goals:
The Java Virtual Machine (JVMTM) 1
Garbage collection
The Java Runtime Environment (JRE)
●
●
●
●

The Java Virtual Machine
a specification that provides runtime environment in which java byte
code can be executed.
Reads compiled byte codes that are platform-independent
JVMs are available for many hardware and software platforms.
JVM is platform dependent because configuration of each OS differs.
The Java Virtual Machine(JVM) make the code run in any platform, thereby
making it platform independent
JVM is platform dependent because configuration of each OS differs.
But, Java is platform independent

Garbage Collection
Allocated memory that is no longer needed should be deallocated.
In other languages, deallocation is the programmer’s responsibility.
The Java programming language provides a system-level thread to
track memory allocation.
●
●
●

Garbage Collection
Garbage collection has the following characteristics:
Checks for and frees memory no longer needed
Is done automatically
Can vary dramatically across JVM implementations
●
●
●

JVM Tasks
The JVM performs
Loads code
Verifies code
Executes code
three main tasks:
●
●
●

The Class Loader
Loads all classes necessary for the execution of a program
Maintains classes of the local file system in separate namespaces
●
●

The Bytecode Verifier
The
The
The
The
code
code
code
adheres to the JVM specification.
does not violate system integrity.
causes no operand stack overflows or underflows.
●
●
●
parameter types for all operational code are●
correct.
No illegal data conversions (the conversion of integers to pointers)
have occurred.
●

Simple
Object-Oriented
Platform independent
Features of Java
Secured
Robust
Architecture neutral
Multithreaded
Distributed

Simple Java Application
The TestGreeting.java Application
//
// Sample "Hello World" application
//
public class TestGreeting{public class TestGreeting{
public static void main (String[]
args)
Greeting hello = new Greeting();
hello.greet();
}
}
{

A Simple Java Application
The Greeting.java Class
public class Greeting {
public void greet() {
System.out.println(“hi”);
}
}

Compiling and Running
the TestGreeting Program
Compile TestGreeting.java:
javac TestGreeting.java
The Greeting.java is compiled
●
automatically.●
Run the application by using the following command:●
java TestGreeting
Locate common compile and runtime errors.●

Java Technology Runtime
Environment

Classes as Blueprints for
Objects
In Java technology, classes support three key features of object-
oriented programming (OOP):
Encapsulation
●
–
Inheritance
Polymorphism
–
– Polymorphism–

Declaring Java Technology
Classes
Basic syntax of a Java class:
<modifier>* class <class_name>
<attribute_declaration>*
<constructor_declaration>*
●
{
<method_declaration>*
}

Declaring Java Technology
Classes
public class Vehicle {
private double maxLoad;
public void setMaxLoad(double
maxLoad = value;
value) {
}
}

Declaring Attributes
Basic syntax of an attribute:●
<modifier>* <type>
<name>
[ = <initial_value>];
Examples:
public class Foo {
●
public class Foo {
private
private
private
}
int x;
float y = 10000.0F;
String name = "Bates Motel";

Declaring Methods
Basic syntax of a method:
<modifier>* <return_type>
<statement>*
}
<name> ( <argument>* ) {

Declaring Methods
public class Dog {
private int weight;
public int getWeight() {
return weight;
}}
public void setWeight(int
if ( newWeight > 0 ) {
weight = newWeight;
}
}
newWeight) {

Accessing Object Members
The dot notation is: <object>.<member>
This is used to access object members, including
methods.
Examples of dot notation are:
d.setWeight(42);
●
attributes and●
●
d.setWeight(42);
d.weight = 42; // only permissible if weight is public

Declaring Constructors
Basic syntax of a constructor:●
[<modifier>] <class_name>
<statement>*
}
Example:
( <argument>* ) {
●
public class Dog {
private int weight;
public Dog() {
weight = 42;
}
}

The Default Constructor
There is always at least one constructor in every class.
If the writer does not supply any constructors, the default
constructor is present automatically:
●
●
The default constructor takes no arguments
The default constructor body is empty
–
– The default constructor body is empty–
The default enables you to create object instances with new
Xxx()without having to write a constructor.
●

Source File Layout
Basic syntax of a Java source file is:
[<package_declaration>]
<import_declaration>*
<class_declaration>+
●

Source File Layout
package shipping.reports;
import
import
import
shipping.domain.*;
java.util.List;
java.io.*;import java.io.*;
public class VehicleCapacityReport
private List vehicles;
{
public void generateReport(Writer output)
{...}
}

Software Packages
Packages help manage large software systems.
Packages can contain classes and sub-packages.
●
●

The package Statement
Basic syntax of the package statement is: package
<top_pkg_name>[.<sub_pkg_name>]*;
●
–
Examples of the statement are:
package shipping.gui.reportscreens;
●
–
Specify the package declaration at the beginning of the source file.Specify the package declaration at the beginning of
Only one package declaration per source file.
the source file.●
●
If no package is declared, then the class is placed into the default
package.
Package names must be hierarchical and separated by dots.
●
●

The import Statement
Basic syntax of the import statement is:
Import<pkg_name>[.<sub_pkg_name>]*.<class_name>;
OR
import<pkg_name>[.<sub_pkg_name>]*.*;
●
Examples of the statement are:●
import
import
import
java.util.List;
java.io.*;
shipping.gui.reportscreens.*;

The import Statement
The import statement does the following:
Precedes all class declarations
Tells the compiler where to find classes
●
●

Comments
The three permissible
styles
program are:
// comment on one line
/* comment on one
of comment in a Java technology
/* comment on one
* or more lines
*/
/** documentation
comment
* can also span one or more
lines
*/

Semicolons, Blocks, and
White Space
A statement is one or more lines of code terminated by a semicolon (;):●
totals = a +
+ d + e + f;
A block is a
and closing
b + c
collection
braces:
of statements bound by opening●
and closing
{
x = y + 1;
y = x + 1;
}
braces:

White Space
A class definition uses
public class MyDate {
a special block:
private
private
int
int
day;
month;
private
}
int year;

White Space
You can nest block statements:
while ( i < large
a = a + i;
// nested block
if ( a == max ) {
) {
if ( a == max ) {
b = b + a;
a = 0;
}
i = i + 1;
}

White Space
Any amount of white
For example:
{int x;x=23*54;}
is equivalent to:
space is permitted in a Java:
{
int x;
x = 23 * 54;
}

Identifiers
Identifiers have the following characteristics:
Are names given to a variable, class, or method
Can start with a Unicode letter, underscore (_),
or
●
dollar sign ($)●
Are case-sensitive
Examples:
and have no maximum length●
● Examples:
identifier
userName
user_name
_sys_var1
$change
●

Keywords
abstract continue for new switch●
assert default goto package
this
synchronized●
boolean do if private●
break
byte
double implements
else import public
protected
throws
throw●
● byte
case
catch
char
class
const
else import public throws●
enum instanceof return transient●
extends int short try●
final interface static void●
finally long strictfp volatile
while
●
floatnative super●

Primitive Types
The Java programming
Logical – boolean
Textual – char
language defines eight primitive types:
●
●
Integral – byte, short, int, and long●
Floating – double and float●

Java Reference Types
In Java technology, beyond primitive types all others are reference
types.
A reference variable contains a handle to an object.
●
●
Car c = new Car();
C is a reference variable
–
– C is a reference variable–

Constructing and
Initializing Objects
Calling new Xyz() performs the following actions:
a. Memory is allocated for the object.
b. Explicit attribute initialization is
performed.
c. A constructor is executed.
●
c. A constructor is executed.
d. The object reference is returned by the
new operator.
The reference to the object is assigned to a variable.
An example is:
MyDate my_birth = new MyDate(22, 7, 1964);
●
●

Memory Allocation and
Layout
A declaration allocates storage only for a reference:
●
Use the new operator to allocate space for MyDate:
●

Executing the Constructor
MyDate my_birth = new MyDate(22, 7, 1964);●

Assigning a Variable
Assign the newly created object to the reference variable as
follows:
●

Assigning References
Two variables refer to a
int x = 7;
int y = x;
single object:
MyDate s = new MyDate(22, 7, 1964);
MyDate t = s;MyDate t = s;

Java Programming Language
Coding Conventions
Packages:
com.example.domain;
●
–
Classes, interfaces, and
SavingsAccount
enum types:●
–
Methods:●
Methods:
GetAccount()–
Variables:
currentCustomer
●
–
Constants:
HEAD_COUNT
●
–

Coding Conventions
Control structures:●
if ( condition
statement1;
} else {
) {
statement2;
}
Spacing:●
Use one statement per line.–
Use two or four spaces for indentation.–

Coding Conventions
Comments:
Use // to comment inline code.
●
–
Use /** documentation */ for class members.–

Variables and Scope
Local variables are:
Variables that are defined inside a method and are called local,
automatic, temporary, or stack variables
Variables that are created when the method is executed are
destroyed when the method is exited
●
●
destroyed when the method is exited
Variable initialization comprises the following:
Local variables require explicit initialization.
Instance variables are initialized automatically.
●
●

Initialization Before
Use Principle
The compiler
before used.
will verify that local variables have been initialized
int
int
int
x=8;
y;
z;int z;
z=x+y;

Logical Operators
The boolean operators
! – NOT
are:●
–
| – OR
& – AND
^ – XOR
–
–
^ – XOR–
The short-circuit
&& – AND
boolean operators are:●
–
|| – OR–

Bitwise Logical Operators
The integer bitwise operators
~ – Complement
are:●
–
^ – XOR
& – AND
| – OR
–
–
| – OR–

Bitwise Logical Operators:
Example

Right-Shift Operators >>
and >>>
Arithmetic or signed right
shift
Examples are:
( >> ) operator:●
●
128 >> 1 returns 128/2 1 = 64
256 >> 4 returns 256/2 4 = 16
-256 >> 4 returns -256/2 4 = -
–
–
-256 >> 4 returns -256/2 4 = -
16
–
The sign bit is copied during the shift.
Logical or unsigned right-shift ( >>> )
operator: This operator is used for bit
patterns.
●
●
–
The sign bit is not copied during the
shift.
–

Left-Shift Operator <<
Left-shift ( << ) operator works as follows:
128 << 1 returns 128 * 2 1 = 256
●
–
16 << 2 returns 16 * 2 2 = 64–

Shift Operator Examples
·101010101010101010101
0101010101010101010101
0101010101110111011101
13
57
)
)
5
s>
>
·l1l1l1l1l1l1l1l1l1l1l
1l1l1l1l1l1l1l1l1l1l1l
1l1l1l1l1lol1lol1lol1I
-
135
7
~1
~s,
s ·lololololol1l1l1l1l1l1
l1l1l1l1l1l1l1l1l1l1l1l
1l1l1l1lol1lol1lol1I
>>
>
1
3
"
5
·1°1°1°1°1°1°1°1°1°1°
1°1°1°1°1°1°111°11lol
1lolol1l1lol11ol01°1°1
°1
(
(
>

String Concatenation With +
The + operator works as follows:
Performs String concatenation
●
–
Produces a new String:–
String salutation = "Dr.";String
String
String
salutation = "Dr.";
name = "Pete" + " " + "Seymour";
title = salutation + " " + name;

Casting
If information might be lost in an assignment, the programmer
must
the assignment with a cast.
confirm●
The assignment between long and int requires
an
long bigValue = 99L;
explicit cast.●
int squashed = bigValue;// Wrong, needs a castint
int
squashed
squashed
=
=
bigValue;// Wrong, needs a cast
(int) bigValue; // OK
int
int
int
squashed
squashed
squashed
=
=
=
99L;// Wrong, needs a cast
(int) 99L;// OK, but...
99; // default integer literal

Promotion and Casting
of Expressions
Variables are promoted automatically to a longer form (such as int
to long).
●
Expression is assignment-compatible if the variable
as large
long bigval = 6;// 6 is an int type, OK
type is at least●
long bigval = 6;// 6 is an int type, OK
int smallval = 99L; // 99L is a long, illegal
double z = 12.414F;// 12.414F is float, OK
float z1 = 12.414; // 12.414 is double, illegal

Simple if, else Statements
The if statement syntax:
if ( <boolean_expression> )
<statement_or_block>
Example:
if ( x < 10 )
●
●
if ( x < 10 )
System.out.println("Are
or (recommended): if (
x < 10 ) {
}
you finished yet?");

Complex if, else Statements
The if-else statement syntax:
else
●
Example:
if ( x < 10 ) {
●
} else {
System.out.println("Keep working...");
}

Complex if, else Statements
The if-else-if statement syntax:
else if ( <boolean_expression> )
●

if-else-if statement: Example
Example:
int count = getCount(); // a method
defined if (count < 0) {
●
in the class
System.out.println("Error: count value is
negative.");
} else if (count > getMaxCount()) {
System.out.println("Error: count value is too
big.");
} else {
System.out.println("There will be " + count
+
" people for lunch today.");
}

Switch Statements
The switch statement syntax:
switch ( <expression> ) {
case <constant1>:
<statement_or_block>*
[break;]
case <constant2>:case <constant2>:
[break;]
default:
[break;]
}

Switch Statement Example
String carModel = ”STANDARD”;
switch ( carModel ) { case
DELUXE:
System.out.println(“DELUXE”);
break;
case STANDARD:
System.out.println(“Standard”);
break;
default:
System.out.println(“Default”);
}

Switch Statements
Without the break statements, the execution falls through each
subsequent case clause.
●

For Loop
The for loop syntax:
for ( <init_expr>; <test_expr>; <alter_expr> )
●

For Loop Example
for ( int i = 0; i < 10; i++ )
System.out.println(i + " squared
or (recommended):
for ( int i = 0; i < 10; i++ ) {
is " + (i*i));
System.out.println(i + " squared
}
is " + (i*i));

While Loop
The while loop syntax:
while ( <test_expr> )

While Loop Example
Example:
int i = 0;
while ( i < 10 ) {
System.out.println(i + " squared is " + (i*i));
i++;
}

The do/while Loop
The do/while loop syntax:
do
while ( <test_expr> );
●

The do/while
Example
Loop:
Example:
int i = 0; do {
System.out.println(i
i++;
●
+ " squared is " + (i*i));
} while ( i < 10 );

Special Loop Flow
Control
The
The
The
break [<label>]; command
continue [<label>]; command
<label> : <statement> command, where <statement> should be
●
●
●
a loop

The break Statement
do {
statement;
if ( condition
break;
) {
}
statement;
} while ( test_expr );

The continue Statement
do {
statement;
if ( condition
continue;
) {
}
statement;
} while ( test_expr );

Using break
with Labels
Statements
outer:
do {
statement1
;
do {
statement2statement2
;
if ( condition ) {
break outer;
}
statement3;
} while ( test_expr
);
statement4;
} while ( test_expr
);

Using continue
with Labels
Statements
test:
do {
statement1;
do {
statement2;
if ( condition ) {if ( condition ) {
continue test;
}
statement3;
} while ( test_expr
statement4;
} while ( test_expr
);
);

Declaring Arrays
Group data objects of the same type.●
Declare arrays
char s[];
int p[];
of primitive or class types:●
char[] s;
int[] p;
Create space for a reference.●
An array is an object; it is created with new.●

Creating Arrays
Use the new keyword to create an arrayobject.
For example, a primitive (char) array:
public char[] createArray()
char[] s;
{
s = new char[26];
for ( int i=0; i<26; i++ ) {
s[i] = (char) (’A’ + i);
}
return s;
}

Creating an Array of
Character Primitives

Creating Reference Arrays
Another example, an object
array:
public Point[] createArray()
Point[] p;
p = new Point[10];
for ( int i=0; i<10; i++ ) {
{
for ( int i=0; i<10; i++ ) {
p[i] = new Point(i, i+1);
}
return p;
}

Initializing Arrays
Initialize an array element.
Create an array with initial
String[] names;
names = new String[3];
●
values.●
names[0]
names[1]
names[2]
=
=
=
"Georgianna";
"Jen";
"Simon";

Multidimensional Arrays
Arrays of arrays:
int[][] twoDim = new int[4][];
twoDim[0] = new int[5];
twoDim[1] = new int[5];
●
int[][] twoDim = new int[][4]; // illegal
Array of four arrays of five integers each:
int[][] twoDim = new int[4][5];
●

Array Bounds
All array subscripts begin at 0:
public void printElements(int[] list) {
for (int i = 0; i < list.length; i++) {
System.out.println(list[i]);
}
}

Using the Enhanced
for Loop
Java 2 Platform, Standard Edition (J2SETM) version 5.0 introduced●
an enhanced for loop for iterating over
public void printElements(int[] list) {
for ( int element : list ) {
System.out.println(element);
arrays:
System.out.println(element);
}
}

Array Resizing
You
You
cannot resize an array.
can use the same reference variable to refer to an entirely new
●
●
array, such as:
int[] myArray = new int[6];
myArray = new int[10];myArray = new int[10];

Copying Arrays
The System.arraycopy() method to copy arrays
//original array
int[] myArray = { 1, 2, 3, 4, 5, 6 };
// new larger array
is:
int[] hold = { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 };
// copy all of the myArray array to the hold
// array, starting with the 0th index
System.arraycopy(myArray, 0, hold, 0, myArray.length);

Java Presentation For Syntax

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