final JPanel left = new JPanel(new GridLayout(3,2,5,5));
left.add(new JButton("1"));
left.add(new JButton("2"));
left.add(new JButton("3"));
left.add(new JButton("4"));
left.add(new JButton("5"));
left.add(new JButton("6"));
final JPanel right = new JPanel(new GridLayout(3,2,5,5));
right.add(new JButton("7"));
right.add(new JButton("8"));
right.add(new JButton("9"));
right.add(new JButton("10"));
right.add(new JButton("11"));
right.add(new JButton("12"));

final CardLayout layout = new CardLayout();
final JPanel pages = new JPanel(layout);
pages.add(left, "left");
pages.add(right, "right");

final JButton showLeft = new JButton("Left");
showLeft.addActionListener(new ActionListener(){
    @Override public void actionPerformed(ActionEvent e){
        layout.show(pages,"left");
    }
});
final JButton showRight = new JButton("Right");
showRight.addActionListener(new ActionListener(){
    @Override public void actionPerformed(ActionEvent e){
        layout.show(pages,"right");
    }
});

final JPanel buttonPanel = new JPanel();
buttonPanel.add(showLeft);
buttonPanel.add(showRight);

final JPanel main = new JPanel(new BorderLayout());
main.add(pages,BorderLayout.CENTER);
main.add(buttonPanel,BorderLayout.SOUTH);