Diploma in Information Technology

Module VIII: Programming with Java

Rasan SamarasingheESOFT Computer Studies (pvt) Ltd.No 68/1, Main Street, Pallegama, Embilipitiya.

Contents1. Introduction to Java2. Features of Java3. What you can create by Java?4. Start Java Programming5. Creating First Java Program6. Java Virtual Machine7. Basic Rules to Remember8. Keywords in Java9. Comments in Java Programs10. Printing Statements11. Primitive Data Types in Java12. Arithmetic Operators13. Assignment Operators14. Comparison Operators15. Logical Operators16. If Statement17. If… Else Statement18. If… Else if… Else Statement19. Nested If Statement

20. While Loop21. Do While Loop22. For Loop23. Reading User Input24. Arrays25. Two Dimensional Arrays26. Objects and Classes27. Java Classes28. Java Objects29. Methods with Return Value30. Methods without Return Value31. Method Overloading32. Variable Types33. Inheritance34. Method Overriding35. Access Modifiers36. Packages37. GUI Applications in Java38. 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 editorCommand 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)

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

Basic Rules to Remember

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

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

Basic Rules to Remember

Name of the program file should exactly match the class name...

Save as MyFirstApp.java

Basic Rules to Remember

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

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

Basic Rules to Remember

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

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

Keywords in Java

Comments in Java Programs

Comments for single line

// this is a single line comment

For multiline

/* this is a multilinecomment*/

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 one\n 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 declarationtype variable_list;

Variable declaration and initializationtype 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){ //Executes when the Boolean expression 2 is true}else if(Boolean_expression 3){ //Executes when the Boolean expression 3 is true}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

if(Boolean_expression 1){ //Executes when the Boolean expression 1 is

true if(Boolean_expression 2){ //Executes when the Boolean expression 2 is

true }}

Nested If Statement

Boolean Expression 1

True

False

StatementsBoolean 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 Keyboardimport 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 ArrayDataType[] ArrayName = new DataType[size];

// Assigning valuesArrayName[index] = value;ArrayName[index] = value;……..

Building a Single Dimensional Array

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

Building a Single Dimensional Array

//using an array initializerDataType[] 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 Objects and Classes

Java Classes

Method

Dog

namecolor

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 AttributesmyPet.name = “Scooby”; myPet.color = “Brown”;

//calling methodmyPet.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 max(int num1, int num2){int result;if (num1 > num2){result = num1;}else{result = num2;}return result;}

Access modifierReturn typeMethod name

parameters

Return valueMethod body

Methods without Return Value

public void print(String txt){System.out.println(“your text: “ + txt)}

Access modifierVoid represents no return valueMethod 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 Variables2. Instance Variables3. 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.

public class Vehicle{int number;String color;static String model;

void Drive(){int speed = 100;System.out.print(“vehicle is driving in “ + speed + “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.

public class Vehicle{int number;String color;static String model;

void Drive(){int speed = 100;System.out.print(“vehicle is driving in “ + speed + “kmph”);}

}

Inheritance

class Vehicle{//attributes and methods}

class Car extends Vehicle{//attributes and methods}

class Van extends Vehicle{//attributes and methods}

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 codeimport <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);

LayoutsmyFrame.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.

How Events Handling Work?

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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