Program to expain Fucus Event in Java

//  Program to expain Fucus Event.
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
/*
<applet code="FocusEventDemo" width="200" height="100">
</applet>
*/
public class FocusEventDemo extends Applet implements FocusListener
{
Button b1, b2, b3;
Label l1, l2;

public void init()
{
 b1=new Button("First"); 
 b2=new Button("Second");
 b3=new Button("Third");
 l1=new Label("Focus Gained.");  
 l2=new Label("Focus Lost.");
 
 add(b1) ; 
 add(b2) ; 
 add(b3);  
 add(l1) ; 
 add(l2);
 b1.addFocusListener(this);
 b2.addFocusListener(this);
 b3.addFocusListener(this);
}
public void focusGained(FocusEvent fe)
{
 if(fe.getSource()==b1)
  l1.setText("Focus gained by : First");
 else if(fe.getSource()==b2)
  l1.setText("Focus gained by : Second" );
 else if(fe.getSource()==b3)
  l1.setText("Focus gained by : Third" );
}