USE ADAPTER CLASSES TO SIMPLIFY GUI APPLICATION CODE
Some interfaces declare non-needed methods in every implementation. 
Typical examples of this type of interface include the 
java.awt.event.Listener subclasses like WindowListener that define many 
different notification events in a single interface. If a new class 
implements such an interface, all the defined methods must be 
implemented to get by the compiler. 

But developers are often only interested in one or two of the available 
event types. In order to avoid having to provide empty implementations 
of all these event types, an Adapter class can be used to minimize the 
work required to use the given interface.

Adapter classes, like java.awt.event.WindowAdapter, provide default 
implementations for their primary interface methods. These classes are 
abstract, so to use them, they need to be subclassed. The simplest way 
to do this is via an anonymous inner class declaration that overrides 
the methods of interest.

Here is an example class that provides notice of two types of window 
events (out of the seven available) and exits the application when the 
window is closed:

import java.util.*; 
import javax.swing.*; 
import java.awt.event.*; 
 
public class WindowAdapterTest 
{ 
 public static void main(String[] args) { 
 
    JFrame win = new JFrame(); 
    win.setSize(100,100); 
    win.setLocation(100,100); 
    win.addWindowListener(new WindowAdapter(){ 
       public void windowOpened(WindowEvent wev) 
       { 
          System.out.println("Window has opened"); 
       } 
       public void windowClosing(WindowEvent wev) 
       { 
          System.out.println("Window is closing"); 
          System.exit(0); 
       } 
       }); 
    win.setVisible(true); 
  } 
}

However, there are drawbacks to this method. Since Adapters are 
classes, rather than interfaces, they must be subclassed and can't be 
used in conjunction with other adapters to add multiple behaviors to a 
single class. Also, if empty or default interface methods 
implementations of interface methods are not acceptable in practice for 
a given interface, then the interface is not a good candidate for an 
Adapter abstract class. When working with AWT Listener interfaces, or 
when designing new APIs for use by other developers, Adapter classes 
provide a useful shortcut to eliminate empty implementations of 
unneeded interface methods.