如何更改JFrame上的面板？

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class PanelChangeExample {
    private JFrame frame;
    private JPanel panel1;
    private JPanel panel2;

    public PanelChangeExample() {
        frame = new JFrame("Panel Change Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 300);

        panel1 = new JPanel();
        panel1.setBackground(Color.RED);
        panel1.add(new JLabel("Panel 1"));

        panel2 = new JPanel();
        panel2.setBackground(Color.BLUE);
        panel2.add(new JLabel("Panel 2"));

        JButton button = new JButton("Change Panel");
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                Container contentPane = frame.getContentPane();
                contentPane.removeAll();
                contentPane.add(panel2);
                contentPane.validate();
            }
        });

        frame.getContentPane().add(panel1);
        frame.getContentPane().add(button, BorderLayout.SOUTH);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new PanelChangeExample();
            }
        });
    }
}