An example of Adapter Classes

Here's a mouse adapter that beeps when the mouse is clicked

import java.awt.*;
import java.awt.event.*;

public class MouseBeeper extends MouseAdapter  {

  public void mouseClicked(MouseEvent evt) {
    Toolkit.getDefaultToolkit().beep();
  }

}

Without extending the MouseAdapter class, I would have had to write the same class like this

import java.awt.*;
import java.awt.event.*;


public class MouseBeeper implements MouseListener  {

  public void mouseClicked(MouseEvent evt) {
    Toolkit.getDefaultToolkit().beep();
  }

  public void mousePressed(MouseEvent evt) {}
  public void mouseReleased(MouseEvent evt) {}
  public void mouseEntered(MouseEvent evt) {}
  public void mouseExited(MouseEvent evt) {}

}

Adapter classes are a minor convenience. You do not need to use the adapter classes if you don't want to.