急求：怎样删除面板上的按钮等相关组件？

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class TestDivide extends JFrame implements ActionListener{

	JButton b1,b2,b3,b4;

	JPanel p1,p2;

     public TestDivide() {

        Container cp=getContentPane();

        b1=new JButton("按钮A");

        b2=new JButton("按钮B");

        b3=new JButton("按钮C");

        b4=new JButton("删除");

        b4.addActionListener(this);

        JPanel p=new JPanel();

        p1=new JPanel();

        p2=new JPanel();

        p1.add(b1); p1.add(b2); p1.add(b3);

        p2.add(b4);

        p.setLayout(new GridLayout(2,1));

        p.add(p1); p.add(p2);

        cp.add(p);

        setSize(300,200);

        setVisible(true);

    }

     public static void main(String sd[]){

         TestDivide frm=new TestDivide();

     }

	@Override

	public void actionPerformed(ActionEvent e) {

		if(e.getSource()==b4){

			//How can I remove those buttons???

			//SOS  SOS........

		}

	}

}