object oriented programming examples

Java AWT
• Java AWT (Abstract Windowing Toolkit) is an API
to develop GUI or window-based application in
java.
• Java AWT components are platform-dependent
i.e. components are displayed according to the
view of operating system.
• AWT is heavyweight i.e. its components uses the
resources of system.
• The java.awt package provides classes for AWT
api such as TextField, Label, TextArea,
RadioButton, CheckBox, Choice, List etc.

Java AWT Hierarchy
• The hierarchy of Java AWT classes are given below.

• Container
• The Container is a component in AWT that can contain another
components like buttons, textfields, labels etc. The classes that extends
Container class are known as container such as Frame, Dialog and Panel.
• Window
• The window is the container that have no borders and menu bars. You
must use frame, dialog or another window for creating a window.
• Panel
• The Panel is the container that doesn't contain title bar and menu bars. It
can have other components like button, textfield etc.
• Frame
• The Frame is the container that contain title bar and can have menu bars.
It can have other components like button, textfield etc.

Useful Methods of Component class
Method Description
public void add(Component c) inserts a component on this
component.
public void setSize(int width,int height) sets the size (width and height) of the
component.
public void setLayout(LayoutManager
m)
defines the layout manager for the
component.
public void setVisible(boolean status) changes the visibility of the component,
by default false.

Java AWT Example
• To create simple awt example, you need a
frame. There are two ways to create a frame
in AWT.
• By extending Frame class (inheritance)
• By creating the object of Frame class
(association)

Simple example of AWT by inheritance
import java.awt.*;
class First extends Frame{
First(){
Button b=new Button("click me");
b.setBounds(30,100,80,30);// setting button position
add(b);//adding button into frame
setSize(300,300);//frame size 300 width and 300 height
setLayout(null);//no layout manager
setVisible(true);//now frame will be visible, by defaul
t not visible
}
public static void main(String args[]){
First f=new First();
}}

Simple example of AWT by association
import java.awt.*;
class First2{
First2(){
Frame f=new Frame();
b.setBounds(30,50,80,30);
f.add(b);
f.setSize(300,300);
f.setLayout(null);
f.setVisible(true);
}
public static void main(String args[]){
First2 f=new First2();
}}

Event and Listener (Java Event
Handling)
• Changing the state of an object is known as an
event. For example, click on button, dragging
mouse etc.
• The java.awt.event package provides many
event classes and Listener interfaces for event
handling.

Event classes and Listener interfaces:
Event Classes Listener Interfaces
ActionEvent ActionListener
MouseEvent MouseListener and MouseMotionListener
MouseWheelEvent MouseWheelListener
KeyEvent KeyListener
ItemEvent ItemListener
TextEvent TextListener
AdjustmentEvent AdjustmentListener
WindowEvent WindowListener
ComponentEvent ComponentListener
ContainerEvent ContainerListener
FocusEvent FocusListener

Steps to perform Event Handling
• Following steps are required to perform event
handling:
1. Implement the Listener interface and
overrides its methods
2. Register the component with the Listener

For registering the component with the Listener, many
classes provide the registration methods. For example:
– Button
• public void addActionListener(ActionListener a){}
– MenuItem
– TextField
• public void addTextListener(TextListener a){}
– TextArea
• public void addTextListener(TextListener a){}
– Checkbox
• public void addItemListener(ItemListener a){}
– Choice
– List

EventHandling Codes:
• We can put the event handling code into one
of the following places:
1. Same class
2. Other class
3. Anonymous class

Example of event handling within class:
import java.awt.*;
import java.awt.event.*;
class AEvent extends Frame implem
ents ActionListener{
TextField tf;
AEvent(){
tf=new TextField();
tf.setBounds(60,50,170,20);
b.setBounds(100,120,80,30);
b.addActionListener(this);
add(b);add(tf);
setSize(300,300);
setLayout(null);
setVisible(true); }
public void actionPerforme
d(ActionEvent e){
tf.setText("Welcome");
}
public static void main(St
ring args[]){
new AEvent();
}
}

Example of event handling by Outer class:
import java.awt.*;
import java.awt.even
t.*;
class AEvent2 extend
s Frame{
TextField tf;
AEvent2(){
tf=new TextField();
tf.setBounds(60,50,1
70,20);
Button b=new Button(
"click me");
b.setBounds(100,120,80,30);
Outer o=new Outer(this);
b.addActionListener(o);//passi
ng outer class instance
add(b);add(tf);
setSize(300,300);
setLayout(null);
setVisible(true);
}
public static void main(String
args[]){
new AEvent2(); }
}

Cont…
import java.awt.event.*;
class Outer implements ActionListener{
AEvent2 obj;
Outer(AEvent2 obj){
this.obj=obj;
}
public void actionPerformed(ActionEvent e)
{
obj.tf.setText("welcome");
}
}

Example of event handling by Annonymous class:
import java.awt.*;
import java.awt.event
.*;
class AEvent3 extends
Frame{
TextField tf;
AEvent3(){
tf=new TextField();
tf.setBounds(60,50,17
0,20);
Button b=new Button("
click me");
b.setBounds(50,120,80
,30);
b.addActionListener(new Acti
onListener(){
public void actionPerformed(
){
tf.setText("hello");
}
});
add(b);add(tf);
setSize(300,300);
setLayout(null);
setVisible(true);
}
public static void main(Stri
ng args[]){
new AEvent3();
}
}

object oriented programming examples

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object oriented programming examples