Discuss the use of event listeners to handle events with suitable example.

When keys are pressed or mouse buttons are clicked, some events are generated. If we specify what to do when an event is generated, then it is known as event handling. Event handling is basically an automatic notification that some action has occurred. There are three things that are done in event handling:

i. Create a class that represents the event handler.

ii. ii. Implement an appropriate interface called “event listener interface” in the above class.

iii. iii. Register the event handler

The event listeners listen for a particular event and whenever the event occurs they fire the action that is registered for them. A suitable example of using event listener to handle mouse click event is given below:

import java.awt.event.*;

import javax.swing.*;

public class EventListener extends JFrame implements ActionListener {

public EventListener(){

JButton btn = new JButton("Click Me");

add(btn);

btn.addActionListener(this); //registering the event handler

setSize(100, 100);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

@Override

public void actionPerformed(ActionEvent e) {

JOptionPane.showMessageDialog(null, "Hello");

}

public static void main(String []a) {

new EventListener();

}

}

Here, whenever the “Click Me” button is clicked, an event is generated and a particular action of opening a dialog box and displaying message “Hello” happens.