求教 请高手帮帮忙

import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class PanelTest extends JFrame{
    private Container container;
    private JPanel panel;
    
    public PanelTest(){
        super("PanelTest");
        panel = new JPanel();
        panel.setLayout(new FlowLayout());
        panel.add(new JButton("这是本来就有的按钮"));
        panel.setBackground(Color.RED);
        panel.addMouseListener(
                new MouseAdapter(){
                    public void mouseClicked(MouseEvent event){
                    //    JOptionPane.showMessageDialog(null, "^");
                        panel.add(new JButton("这是单击面板后创建的按钮"));
                        pack();
                    }
                }
        );
        container = getContentPane();
        container.add(panel);
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }
    public static void main(String[] args) {
        new PanelTest();
    }
}