How can you handle events using adapter classes? Discuss.

Adapter classes such as KeyAdapter, MouseAdapter, MouseMotionAdapter, WindowAdapter, etc provides the default (generally empty) implementation of all methods for many of the event listener interfaces such as KeyListener, MouseListener, MouseMotionListener, WindowListener, etc. Adapter classes are very useful when you want to process only few of the events that are handled by a particular event listener interface. For example, the KeyListener interface contains three methods KeyPressed(), KeyReleased() and KeyTyped(). If we implement this interface, we have to give implementation of all these three methods. However, by using the KeyAdapter class, we can override only the method that is needed. This can be shown in the code example given below. Here we are writing a GUI program that accepts user input in a text field and displays the key typed in another text field when the pressed key is released. The first program uses KeyListener interface and the second program uses KeyAdapter class.

First program

//KeyListenerTest.java

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class KeyListenerTest extends JFrame {

JTextField t1 = new JTextField(10);

JTextField t2 = new JTextField(10);

public KeyListenerTest() {

setLayout(new FlowLayout());

setSize(200, 200);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

add(t1); ‘

add(t2);

t2.setEditable(false);

t1.addKeyListener(new KeyListener() {

@Override

public void keyTyped(KeyEvent e) { }

@Override

public void keyPressed(KeyEvent e) { }

@Override

public void keyReleased(KeyEvent e) {

String copy = t1.getText();

t2.setText(copy);

}

});

}

public static void main(String[] args) {

new KeyListenerTest(); } }

Second program

//KeyAdapterTest.java

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class KeyAdapterTest extends JFrame {

JTextField t1 = new JTextField(10);

JTextField t2 = new JTextField(10);

public KeyAdapterTest() {

setLayout(new FlowLayout());

setSize(200, 200);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

add(t1);

add(t2);

t2.setEditable(false);

t1.addKeyListener(new KeyAdapter() {

@Override

public void keyReleased(KeyEvent e) {

String copy = t1.getText();

t2.setText(copy);

}

});

}

public static void main(String[] args) {

new KeyAdapterTest();

}

}