Swing problem

import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JPanel;public class MyFrame extends JFrame {	private static final long serialVersionUID = 1L;	JPanel pane;	JPanel pane2;	JButton button;	JLabel label;		public MyFrame() {		super();		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);		pane = new JPanel();		button = new JButton("A");		label = new JLabel("B");		button.addActionListener(new ActionListener() {			public void actionPerformed(ActionEvent e) {				pane2 = new JPanel();				pane2.add(label);				setContentPane(pane2);			}		});		pane.add(button);		setSize(200,200);		this.setContentPane(pane);	}		public static void main(String[] args) {		MyFrame frame = new MyFrame();		frame.setVisible(true);	}}