When we click on button in a frame, some action generates, as a result the state of an object change which is known as JAVA event.

In delegation model, an event is an object that describes a state change in a source. Some of the activities that cause events to be generated are clicking a button, entering a character via the keyboard, selecting an item in a list, and clicking the mouse.

Events may occur that are not directly caused by interactions with a user interface. For example, an event may be generated when a timer expires, a counter exceeds a value, a software or hardware failure occurs, or an operation is completed.

Events are supported by a number of packages like java.util, java.awt, and java.awt.event. The java.awt.event package provides many event classes and Listener interfaces for event handling.

Components of Event Handling:

Event handling has three main components,

• • Events : An event is a change of state of an object.
• • Events Source : Event source is an object that generates an event.
• • Listeners : A listener is an object that listens to the event. A listener gets notified when an event occurs.

Event Classes and Listener Interfaces:

How to perform Event Handling:

To perform event handling, we have to follow the following two steps:

1. Implement the Listener interface and overrides its methods
2. Register the component with the Listener

Example of Event Handling within Class

import java.awt.*;
import java.awt.event.*;
class DemoEvent extends Frame implements ActionListener
{
	TextField tf;
	DemoEvent()
	{
		tf=new TextField();
		tf.setBounds(60,50,170,20);
		Button b=new Button("click me");
		b.setBounds(100,120,80,30);
		b.addActionListener(this);
		add(b);add(tf);
		setSize(300,300);
		setLayout(null);
		setVisible(true);
	}
	public void actionPerformed(ActionEvent e)
	{
		tf.setText("Welcome 2 SILAN SOFTWARE");
	}
	public static void main(String[] args)
	{
		new DemoEvent();
	}
}

Output:

Example of Event Handling by Outer Class

import java.awt.*;
import java.awt.event.*;
class DemoEvent2 extends Frame
{
	TextField tf;
	DemoEvent2()
	{
		tf=new TextField();
		tf.setBounds(60,50,170,20);
		Button b=new Button("OK");
		b.setBounds(100,120,80,30);
		Outer ob=new Outer(this);
		b.addActionListener(ob); //passing outer class instance
		add(b);add(tf);
		setSize(300,300);
		setLayout(null);
		setVisible(true);
	}
	public static void main(String[] args)
	{
		new DemoEvent2();
	}
}
class Outer implements ActionListener
{
	DemoEvent2 obj;
	Outer(DemoEvent2 obj)
	{
		this.obj=obj;
	}
	public void actionPerformed(ActionEvent e)
	{
		obj.tf.setText("SILAN SOFTWARE");
	}
}

Output:

Example of event handling by Annonymous class

import java.awt.*;
import java.awt.event.*;
class DemoEvent3 extends Frame
{
	TextField tf;
	DemoEvent3()
	{
		tf=new TextField();
		tf.setBounds(60,50,170,20);
		Button b=new Button("OK");
		b.setBounds(50,120,80,30);
		b.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				tf.setText("SILAN SOFTWARE");
			}
		});
		add(b);add(tf);
		setSize(300,300);
		setLayout(null);
		setVisible(true);
	}
	public static void main(String[] args)
	{
		new DemoEvent3();
	}
}

Output: