DITEC - Programming with Java

Diploma in Information Technology
Module VIII: Programming with Java
Rasan Samarasinghe
ESOFT Computer Studies (pvt) Ltd.
No 68/1, Main Street, Pallegama, Embilipitiya.

Contents
1. Introduction to Java
2. Features of Java
3. What you can create by Java?
4. Start Java Programming
5. Creating First Java Program
6. Java Virtual Machine
7. Basic Rules to Remember
8. Keywords in Java
9. Comments in Java Programs
10. Printing Statements
11. Primitive Data Types in Java
12. Arithmetic Operators
13. Assignment Operators
14. Comparison Operators
15. Logical Operators
16. If Statement
17. If… Else Statement
18. If… Else if… Else Statement
19. Nested If Statement
20. While Loop
21. Do While Loop
22. For Loop
23. Reading User Input
24. Arrays
25. Two Dimensional Arrays
26. Objects and Classes
27. Java Classes
28. Java Objects
29. Methods with Return Value
30. Methods without Return Value
31. Method Overloading
32. Variable Types
33. Inheritance
34. Method Overriding
35. Access Modifiers
36. Packages
37. GUI Applications in Java
38. Java Applets

Introduction to Java
• Developed by Sun Microsystems (has merged
into Oracle Corporation later)
• Initiated by James Gosling
• Released in 1995
• Java has 3 main versions as Java SE, Java EE
and Java ME

Features of Java
 Object Oriented
 Platform independent
 Simple
 Secure
 Portable
 Robust
 Multi-threaded
 Interpreted
 High Performance

What you can create by Java?
• Desktop (GUI) applications
• Enterprise level applications
• Web applications
• Web services
• Java Applets
• Mobile applications

Start Java Programming
What you need to program in Java?
Java Development Kit (JDK)
Microsoft Notepad or any other text editor
Command Prompt

Creating First Java Program
public class MyFirstApp{
public static void main(String[] args){
System.out.println("Hello World");
}
}
MyFirstApp.java

Java Virtual Machine (JVM)
1. When Java source code (.java files) is
compiled, it is translated into Java bytecodes
and then placed into (.class) files.
2. The JVM executes Java bytecodes and run
the program.
Java was designed with a concept of write once and
run anywhere. Java Virtual Machine plays the
central role in this concept.

Basic Rules to Remember
Java is case sensitive…
Hello not equals to hello

Class name should be a single word and it
cannot contain symbols and should be started
with a character…
Wrong class name Correct way
Hello World HelloWorld
Java Window Java_Window
3DUnit Unit3D
“FillForm” FillForm

}
}
Name of the program file should exactly match
the class name...
Save as MyFirstApp.java

Main method which is a mandatory part of
every java program…
}
}

Tokens must be separated by Whitespaces
Except ( ) ; { } . [ ] + - * /
}
}

Comments in Java Programs
Comments for single line
// this is a single line comment
For multiline
/*
this is
a multiline
comment
*/

Printing Statements
System.out.print(“your text”); //prints text
System.out.println(“your text”); //prints text
and create a new line
System.out.print(“line onen line two”);//prints
text in two lines

Primitive Data Types in Java
Keyword Type of data the variable will store Size in memory
boolean true/false value 1 bit
byte byte size integer 8 bits
char a single character 16 bits
double double precision floating point decimal number 64 bits
float single precision floating point decimal number 32 bits
int a whole number 32 bits
long a whole number (used for long numbers) 64 bits
short a whole number (used for short numbers) 16 bits

Variable Declaration in Java
Variable declaration
type variable_list;
Variable declaration and initialization
type variable_name = value;

Variable Declaration in Java
int a, b, c; // declares three ints, a, b, and c.
int d = 3, e, f = 5; // declares three more ints,
initializing d and f.
byte z = 22; // initializes z.
double pi = 3.14159; // declares an approximation
of pi.
char x = 'x'; // the variable x has the value 'x'.

Arithmetic Operators
Operator Description Example
+ Addition A + B will give 30
- Subtraction A - B will give -10
* Multiplication A * B will give 200
/ Division B / A will give 2
% Modulus B % A will give 0
++ Increment B++ gives 21
-- Decrement B-- gives 19
A = 10, B = 20

Assignment Operators
Operator Example
= C = A + B will assign value of A + B into C
+= C += A is equivalent to C = C + A
-= C -= A is equivalent to C = C - A
*= C *= A is equivalent to C = C * A
/= C /= A is equivalent to C = C / A
%= C %= A is equivalent to C = C % A

Comparison Operators
Operator Example
== (A == B) is false.
!= (A != B) is true.
> (A > B) is false.
< (A < B) is true.
>= (A >= B) is false.
<= (A <= B) is true.
A = 10, B = 20

Logical Operators
Operator Name Example
&& AND (A && B) is False
|| OR (A || B) is True
! NOT !(A && B) is True
A = True, B = False

If Statement
if(Boolean_expression){
//Statements will execute if the Boolean
expression is true
}

If Statement
Boolean
Expression
Statements
True
False

If… Else Statement
if(Boolean_expression){
//Executes when the Boolean expression is
true
}else{
//Executes when the Boolean expression is
false
}

If… Else Statement
Boolean
Expression
Statements
True
False
Statements

If… Else if… Else Statement
if(Boolean_expression 1){
//Executes when the Boolean expression 1 is true
}else if(Boolean_expression 2){
}else if(Boolean_expression 3){
}else {
//Executes when the none of the above condition
is true.
}

If… Else if… Else Statement
Boolean
expression 1
False
Statements
Boolean
expression 2
Boolean
expression 3
Statements
Statements
False
False
Statements
True
True
True

Nested If Statement
//Executes when the Boolean expression 1 is
true
//Executes when the Boolean expression 2 is
true
}
}

Nested If Statement
Boolean
Expression 1
True
False
Statements
Boolean
Expression 2
True
False

While Loop
while(Boolean_expression){
//Statements
}

While Loop
Boolean
Expression
Statements
True
False

Do While Loop
do{
//Statements
}while(Boolean_expression);

Do While Loop
Boolean
Expression
Statements
True
False

For Loop
for(initialization; Boolean_expression; update){
//Statements
}

For Loop
Boolean
Expression
Statements
True
False
Update
Initialization

Nested Loop
Boolean
Expression
True
False
Boolean
Expression
Statements
True
False

Reading User Input by the Keyboard
import java.io.*;
public class DemoApp{
public static void main(String [] args) throws IOException{
BufferedReader br = new BufferedReader(new
InputStreamReader(System.in));
System.out.print(“Enter your text: “);
String txt = br.readLine();
System.out.println(“You have entered:” + txt);
}
}

Arrays
10 30 20 50 15 35
0 1 2 3 4 5
Size = 6
Element Index No
An Array can hold many values in a same
data type under a single name
A single dimensional array

Building a Single Dimensional Array
// Creating an Array
DataType[] ArrayName = new DataType[size];
// Assigning values
ArrayName[index] = value;
ArrayName[index] = value;
……..

char[] letters = new char[4];
letters[0] = ‘a’;
letters[1] = ‘b’;
letters[2] = ‘c’;
letters[3] = ‘d’;
0 1 2 3
a b c d
0 1 2 3
letters
letters
Values in an Array can access
by referring index number

//using an array initializer
DataType[] ArrayName = {element 1, element 2,
element 3, … element n}
int[] points = {10, 20, 30, 40, 50}; 10 20 30 40
0 1 2 3
points
50
4

Manipulating Arrays
Finding the largest
value of an Array
Sorting an Array
15
50
35
25
10
2
1
5
4
3
1
2
3
4
5

Two Dimensional Arrays
10 20 30
100 200 300
0 1 2
0
1
int[][] abc = new int[2][3];
abc[0][0] = 10;
abc[0][1] = 20;
abc[0][2] = 30;
abc[1][0] = 100;
abc[1][1] = 200;
abc[1][2] = 300;
Rows Columns
Column Index
Row Index

Java Classes
Method
Dog
name
color
bark()
class Dog{
String name;
String color;
public Dog(){
}
public void bark(){
System.out.println(“dog is barking!”);
}
}
Attributes
Constructor

Java Objects
Dog myPet = new Dog(); //creating an object
//Assigning values to Attributes
myPet.name = “Scooby”;
myPet.color = “Brown”;
//calling method
myPet.bark();

Methods
Method is a group of statements to perform a
specific task.
• Methods with Return Value
• Methods without Return Value

Methods with Return Value
public int num1, int num2){
int result;
if (num1 > num2){
result = num1;
}else{
result = num2;
}
return result;
}
Access modifier
Return type
Method name
parameters
Return value
Method body

Methods without Return Value
public void {
System.out.println(“your text: “ + txt)
}
Access modifier
Void represents no return value
Method name
parameter
Method
body

Method Overloading
public class Car{
public void Drive(){
System.out.println(“Car is driving”);
}
public void Drive(int speed){
System.out.println(“Car is driving in ” + speed +
“kmph”);
}
}

Variable Types
Variables in a Class can be categorize into
three types
1. Local Variables
2. Instance Variables
3. Static/Class Variables

Local Variables
• Declared in methods,
constructors, or blocks.
• Access modifiers cannot
be used.
• Visible only within the
declared method,
constructor or block.
• Should be declared with
an initial value.
public class Vehicle{
int number;
String color;
static String model;
void Drive(){
int speed = 100;
System.out.print(“vehicle
is driving in “ + speed +
“kmph”);
}
}

Instance Variables
• Declared in a class, but
outside a method,
constructor or any block.
• Access modifiers can be
given.
• Can be accessed directly
anywhere in the class.
• Have default values.
• Should be called using an
object reference to access
within static methods and
outside of the class.
int number;
String color;
void Drive(){
int speed = 100;
“kmph”);
}
}

Static/Class Variables
• Declared with the static
keyword in a class, but
outside a method,
constructor or a block.
• Only one copy for each
class regardless how
many objects created.
• Have default values.
• Can be accessed by
calling with the class
name.
int number;
String color;
void Drive(){
int speed = 100;
“kmph”);
}
}

Inheritance
class Vehicle{
//attributes and methods
}
class Car extends Vehicle{
}
class Van extends Vehicle{
}
Vehicle
Car Van

Method Overriding
class Vehicle{
public void drive(){
System.out.println(“Vehicle is driving”);
}
}
class Car extends Vehicle{
public void drive(){
System.out.println(“Car is driving”);
}
}

Access Modifiers
Access
Modifiers
Same
class
Same
package
Sub class
Other
packages
public Y Y Y Y
protected Y Y Y N
No access
modifier
Y Y N N
private Y N N N

Packages
A Package can be defined as a grouping of
related types (classes, interfaces,
enumerations and annotations) providing
access protection and namespace
management.
//At the top of your source code
import <package name>.*;
import <package name>.<class name>;

GUI Applications in Java
• Abstract Window Toolkit
• Frame Class
• Layouts
• Label Class
• TextField Class
• Button Class
• Events

Abstract Window Toolkit
The Abstract Window Toolkit (AWT) is a
package of JDK classes for creating GUI
components such as buttons, menus, and
scrollbars for applets and standalone
applications.
import java.awt.*;

Frame Class
Frame myFrame = new Frame(“My Frame”);
myFrame.setSize(300,200);
myFrame.setVisible(true);

Layouts
myFrame.setLayout(new FlowLayout()); myFrame.setLayout(new GridLayout(2,3));
myFrame.setLayout(null);

Label Class
Label lbl = new Label("Hello World");
lbl.setBounds(120,40,120,25);
myFrame.add(lbl);

TextField Class
TextField txt = new TextField();
txt.setBounds(100,90,120,25);
myFrame.add(txt);

Button Class
Button btn = new Button("OK");
btn.setBounds(120,150,60,25);
myFrame.add(btn);

Events
An event is when something special happens within a
Graphical User Interface.
Things like buttons being clicked, the mouse moving,
text being entered into text fields, the program closing,
etc.. then an event will trigger.

Java Applets
An applet is a Java program that runs in a Web
browser.

Creating a Java Applet
import java.applet.*;
import java.awt.*;
public class HelloWorldApplet extends Applet {
public void paint (Graphics g) {
g.drawString ("Hello World", 25, 50);
}
}
<applet code="HelloWorldApplet.class" width="320"
height="120"></applet>
Write a Java Applet and
compile it
Embed it in a HTML file

The End
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DITEC - Programming with Java

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