Hinzufügen der JPanels aus anderen Klassen zum cardLayout

Hatte ich ein kleines Programm, hoffentlich werden die Kommentare in das Programm, vielleicht in der Lage sein, Sie zu führen, um zu verstehen, wie CardLayout.

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

/* Here we are first declaring our class that will act as the
 * base for other panels or in other terms the base for CardLayout.
 */

public class CardLayoutTest
{
    private static final String CARD_JBUTTON =  "Card JButton";
    private static final String CARD_JTEXTFIELD = "Card JTextField";    
    private static final String CARD_JRADIOBUTTON = "Card JRadioButton";

    private static void createAndShowGUI()
    {
        JFrame frame = new JFrame("Card Layout Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);

        //This JPanel is the base for CardLayout for other JPanels.
        final JPanel contentPane = new JPanel();
        contentPane.setLayout(new CardLayout(20, 20));

        /* Here we be making objects of the Window Series classes
         * so that, each one of them can be added to the JPanel 
         * having CardLayout. 
         */
        Window1 win1 = new Window1();
        contentPane.add(win1, CARD_JBUTTON);
        Window2 win2 = new Window2();
        contentPane.add(win2, CARD_JTEXTFIELD);
        Window3 win3 = new Window3();
        contentPane.add(win3, CARD_JRADIOBUTTON);

        /* We need two JButtons to go to the next Card
         * or come back to the previous Card, as and when
         * desired by the User.
         */
        JPanel buttonPanel = new JPanel(); 
        final JButton previousButton = new JButton("PREVIOUS");
        previousButton.setBackground(Color.BLACK);
        previousButton.setForeground(Color.WHITE);
        final JButton nextButton = new JButton("NEXT");
        nextButton.setBackground(Color.RED);
        nextButton.setForeground(Color.WHITE);
        buttonPanel.add(previousButton);
        buttonPanel.add(nextButton);

        /* Adding the ActionListeners to the JButton,
         * so that the user can see the next Card or
         * come back to the previous Card, as desired.
         */
        previousButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                CardLayout cardLayout = (CardLayout) contentPane.getLayout();
                cardLayout.previous(contentPane);
            }
        });
        nextButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                CardLayout cardLayout = (CardLayout) contentPane.getLayout();
                cardLayout.next(contentPane);   
            }
        });

        //Adding the contentPane (JPanel) and buttonPanel to JFrame.
        frame.add(contentPane, BorderLayout.CENTER);
        frame.add(buttonPanel, BorderLayout.PAGE_END);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
} 

class Window1 extends JPanel
{
    /*
     * Here this is our first Card of CardLayout, which will
     * be added to the contentPane object of JPanel, which
     * has the LayoutManager set to CardLayout.
     * This card consists of Two JButtons.
     */  
    private ActionListener action;

    public Window1() 
    {
        init();
    }

    private void init() 
    {
        final JButton clickButton = new JButton("CLICK ME");
        final JButton dontClickButton = new JButton("DON\'T CLICK ME");     

        action = new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                if (ae.getSource() == clickButton)
                {
                    JOptionPane.showMessageDialog(null, "Hello there dude!"
                                                , "Right Button", JOptionPane.INFORMATION_MESSAGE);
                }
                else if (ae.getSource() == dontClickButton)
                {
                    JOptionPane.showMessageDialog(null, "I told you not to click me!"
                                                        , "Wrong Button", JOptionPane.PLAIN_MESSAGE);
                }
            }
        };

        clickButton.addActionListener(action);
        dontClickButton.addActionListener(action);

        add(clickButton);
        add(dontClickButton);
    }
}

class Window2 extends JPanel implements ActionListener 
{
    /*
     * Here this is our second Card of CardLayout, which will
     * be added to the contentPane object of JPanel, which
     * has the LayoutManager set to CardLayout.
     * This card consists of a JLabel and a  JTextField
     * with GridLayout.
     */  

    private JTextField textField;

    public Window2() 
    {
        init();
    }

    private void init() 
    {
        setLayout(new GridLayout(1, 2));
        JLabel userLabel = new JLabel("Your Name : ");
        textField = new JTextField();
        textField.addActionListener(this);

        add(userLabel);
        add(textField);
    }

    public void actionPerformed(ActionEvent e) 
    {            
        if (textField.getDocument().getLength() > 0)
            JOptionPane.showMessageDialog(null, "Your Name is : " + textField.getText()
                                                                            , "User\'s Name : ", JOptionPane.QUESTION_MESSAGE);
    }
}

class Window3 extends JPanel
{
    /*
     * Here this is our third Card of CardLayout, which will
     * be added to the contentPane object of JPanel, which
     * has the LayoutManager set to CardLayout.
     * This card consists of Two JLabels and two JCheckBox
     * with GridLayout.
     */  
    private ActionListener state;

    public Window3()
    {
        init();
    }

    public void init()
    {
        setLayout(new GridLayout(2, 2));
        JLabel maleLabel = new JLabel("MALE", JLabel.CENTER);
        final JCheckBox maleBox = new JCheckBox();
        JLabel femaleLabel = new JLabel("FEMALE", JLabel.CENTER);
        final JCheckBox femaleBox = new JCheckBox();

        state = new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                if (maleBox == (JCheckBox) ae.getSource())
                {
                    femaleBox.setSelected(false);
                    JOptionPane.showMessageDialog(null, "Congrats you are a Male"
                                                , "Gender : ", JOptionPane.INFORMATION_MESSAGE);                            
                }
                else if (femaleBox == (JCheckBox) ae.getSource())
                {
                    maleBox.setSelected(false);
                    JOptionPane.showMessageDialog(null, "Congrats you are a Female"
                                            , "Gender : ", JOptionPane.INFORMATION_MESSAGE);                        
                }
            }
        };

        maleBox.addActionListener(state);
        femaleBox.addActionListener(state);
        add(maleLabel);
        add(maleBox);
        add(femaleLabel);
        add(femaleBox);
    }
}