Determine when a component is added or removed from a container (Java)

*****************************************************************
COMPLETE SOURCE CODE FOR : DetermineWhenAComponentIsAddOrRemove.java
*****************************************************************
import java.awt.Frame;//import Frame class into program
import java.awt.Panel;//import Panel class into program
import java.awt.Button;//import Button class into program
import java.awt.Label;//import Label class into program
import java.awt.Component;//import Component class into program

import java.awt.event.ContainerListener;//import ContainerListener class into program
import java.awt.event.ContainerAdapter;//import ContainerAdapter class into program
import java.awt.event.ContainerEvent;//import ContainerEvent class into program

import java.awt.event.WindowListener;//import WindowListener class into program
import java.awt.event.WindowAdapter;//import WindowAdapter class into program
import java.awt.event.WindowEvent;//import WindowEvent class into program

import java.awt.event.ActionListener;//import ActionListener class into program
import java.awt.event.ActionEvent;//import ActionEvent class into program

import java.awt.BorderLayout;//import BorderLayout class into program
import java.awt.FlowLayout;//import FlowLayout class into program

import java.awt.Color;//import Color class into program

import javax.swing.JOptionPane;//import JOptionPane class into program

public class DetermineWhenAComponentIsAddOrRemove implements ActionListener
{
 //Initiate Frame(a) object
 Frame a=new Frame("DETERMINE WHEN A COMPONENT IS ADD OR REMOVE");
 //Initiate Button(b) object
 Button b=new Button("CLICK HERE TO ADD NEW COMPONENT(A LABEL)");
 //Initiate Button(d) object
 Button d=new Button("CLICK HERE TO REMOVE NEW INSERTED COMPONENT");
 //Initiate Panel(c) object
 Panel c=new Panel();

 public DetermineWhenAComponentIsAddOrRemove()
 {
  //Set layout for Frame(a)
  a.setLayout(new BorderLayout());
 
  //Listen when someone click at Frame(a) close button
  WindowListener wl=new WindowAdapter()
  {
   public void windowClosing(WindowEvent evt)
   {
    System.exit(0);
   }
  };
 
  //Listen when a component is added or removed from Panel(c)
  ContainerListener cl=new ContainerAdapter()
  {
   public void componentAdded(ContainerEvent evt)
   {
    JOptionPane.showMessageDialog(null,"A COMPONENT ADDED");
   }
  
   public void componentRemoved(ContainerEvent evt)
   {
    JOptionPane.showMessageDialog(null,"A COMPONENT REMOVED");
   }
  };
 
  //Label at the top of Frame(a)
  Label e=new Label("PANEL WITH BLUE COLOR AT THE CENTER IS A CONTAINER");
  //Make Label's allignment to center
  e.setAlignment(Label.CENTER);
  //Add Label(e) to Frame(a)
  a.add(e,BorderLayout.NORTH);
 
  //Add ContainerListener to Panel(c)
  c.addContainerListener(cl);
  //Set background color(blue) to Panel(c)
  c.setBackground(Color.BLUE);
  //Add Panel(c) to Frame(a)
  a.add(c,BorderLayout.CENTER);
 
  //Panel to place Button(b and d)
  Panel f=new Panel();
  //Set layout for panel(f)
  f.setLayout(new FlowLayout());
  //Add ActionListener to Button(b and d)
  b.addActionListener(this);
  d.addActionListener(this);
  //Add button(b and d) to Panel(f)
  f.add(b);
  f.add(d);
  //Add Panel(f) to Frame(a)
  a.add(f,BorderLayout.SOUTH);
 
  //Add WindowListener to Frame(a)
  a.addWindowListener(wl);
  //Set Frame(a) size to 800pixel width and 600pixel height
  a.setSize(800,600);
  //Set Frame(a) to visible
  a.setVisible(true);
 }

 //Action that must do by Button(b and d)
 public void actionPerformed(ActionEvent evt)
 {
  //Action for Button b
  if(evt.getSource()==b)
  {
   c.add(new Label("NEW LABEL"));
   c.validate();
   a.validate();
  }
 
  //Action for Button d
  if(evt.getSource()==d)
  {
   Component[]storeAllComponent=c.getComponents();
   if(storeAllComponent.length!=0)
   {
    int numbersOfComponent=storeAllComponent.length;
    int indexForRemoveComponent=numbersOfComponent-1;
    c.remove(indexForRemoveComponent);
    c.validate();
    a.validate();
   }
  }
 }

 //MAIN METHOD
 public static void main(String[]args)
 {
  DetermineWhenAComponentIsAddOrRemove myObject=new DetermineWhenAComponentIsAddOrRemove();
 }
}


*****************************************************************
JUST COMPILE AND EXECUTE IT
*****************************************************************