Swing: Panel austauschen, Anfängerfrage?

package de.perdian.test;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PanelTest {

  public static void main(String[] args) {
    TheFrame frame      = TheFrame.getInstance();
    frame.setContentPane(new ThePanel1());
    frame.setBounds(10, 10, 200, 200);
    frame.setVisible(true);
  }

}

class TheFrame extends JFrame {
  
  private static TheFrame myInstance     = new TheFrame();
  
  /**
   * Private singleton constructor
   */
  private TheFrame() {
  }
  
  /**
   * Gets the globall singleton instance
   */
  public static TheFrame getInstance() {
    return TheFrame.myInstance;
  }
  
}

class ThePanel1 extends JPanel {
  public ThePanel1() {
    super(new BorderLayout());
    JButton button1     = new JButton(new AbstractAction("Panel2 anzeigen") {
      public void actionPerformed(ActionEvent e) {
        TheFrame frame  = TheFrame.getInstance();
        frame.setContentPane(new ThePanel2());
        frame.validate();
        frame.repaint();
      }
    });
    this.add(button1, BorderLayout.CENTER);
  }
}

class ThePanel2 extends JPanel {
  public ThePanel2() {
    super(new BorderLayout());
    JButton button2     = new JButton(new AbstractAction("Zurück zu Panel 1") {
      public void actionPerformed(ActionEvent e) {
        TheFrame frame  = TheFrame.getInstance();
        frame.setContentPane(new ThePanel1());
        frame.validate();
        frame.repaint();
      }
    });
    this.add(button2, BorderLayout.CENTER);
  }
}