java - コンボボックスの下にボタンを配置する

Question

ここでコンボボックスの下にボタンを表示するにはどうすればよいですか? つまり、コンボ ボックスのすぐ下にボタン 1 とボタン 2 がありますか?

public class GUI extends JFrame implements ListSelectionListener, ActionListener {

    private JPanel myPanelA;
    private JSplitPane itemPane;

    public static void startWindowsGui ( ) { 

        SwingUtilities.invokeLater ( new Runnable ( ) {
            public void run ( ) {

                GUI gui = new GUI ( );


                gui.setVisible ( true );
            }
        } );
    }

    public GUI() {

        // Set the layout to a grid
        setLayout ( new BorderLayout ( 5, 5 ) );


        setTitle ( "UI " );
        setSize ( 800, 600 );
        setDefaultCloseOperation ( EXIT_ON_CLOSE );
        setBackground ( new Color ( 15, 255, 10 ) );


        addComponents ( );
    }

    private void addComponents ( ) {

        JSplitPane mainPane = new JSplitPane ( JSplitPane.HORIZONTAL_SPLIT );
        itemPane = new JSplitPane ( JSplitPane.VERTICAL_SPLIT );

        mainPane.add ( PanelA ( ), JSplitPane.LEFT );
        mainPane.add ( itemPane, JSplitPane.RIGHT );
        mainPane.setOneTouchExpandable ( true );

        itemPane.setOpaque(true);
        itemPane.setBackground(new Color(0xffffffc0));
        BufferedImage myPicture = null;
        try {
            myPicture = ImageIO.read(new File("C:/Users/Desktop/image.jpg"));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        JLabel picLabel = new JLabel(new ImageIcon(myPicture));
        //add(picLabel);
        itemPane.add(picLabel);

        add ( mainPane, BorderLayout.CENTER );
    }


    private JPanel PanelA ( ) {

        myPanelA = new JPanel ( );


        myPanelA.setLayout ( new BorderLayout ( 0, 0 ) );


        myPanelA.add ( buttonPanel ( ), BorderLayout.NORTH );

        myPanelA.setBorder ( new EmptyBorder ( 0, 0, 0, 0 ) );
        myPanelA.setBackground(new Color(0,0,0));

        return myPanelA;
    }

    @Override
    public void actionPerformed(ActionEvent e) {


    }

    @Override
    public void valueChanged(ListSelectionEvent arg0) {


    }


    private JPanel buttonPanel ( ) {
        // Create the panel 
        JPanel addButton = new JPanel ( );

        JPanel cards; //a panel that uses CardLayout
         String BUTTONPANEL = "Card with JButtons";
         String TEXTPANEL = "Card with JTextField";

        JPanel comboBoxPane = new JPanel(); //use FlowLayout
        String comboBoxItems[] = { BUTTONPANEL, TEXTPANEL };
        JComboBox cb = new JComboBox(comboBoxItems);
        cb.setEditable(false);
            //cb.addItemListener(this);
            comboBoxPane.add(cb);

            //Create the "cards".
            JPanel card1 = new JPanel();
            card1.add(new JButton("Button 1"));
            card1.add(new JButton("Button 2"));

            JPanel card2 = new JPanel();
            card2.add(new JTextField("TextField", 10));

            //Create the panel that contains the "cards".
            cards = new JPanel(new CardLayout());
            cards.add(card1, BUTTONPANEL);
            cards.add(card2, TEXTPANEL);

            addButton.add(comboBoxPane, BorderLayout.PAGE_START);
            addButton.add(cards, BorderLayout.CENTER);

        return addButton;
    }
}