Dynamically create a button, but what happened?

[love2java]

I am new to Swing GUI, now I have a button1, and I want to create a new button in a panel named centerPanel when I click button1, so my code like this:

Code:

public class TestButton extends JFrame {
    public static void main(String args[]) {
        try {
            TestButton frame = new TestButton();
            frame.setVisible(true);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public TestButton() {
        super();
        setBounds(100, 100, 500, 375);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JPanel center = new JPanel();
        getContentPane().add(center, BorderLayout.CENTER);

        final JPanel south = new JPanel();
        getContentPane().add(south, BorderLayout.SOUTH);

        final JButton button = new JButton();
        button.addActionListener(new ActionListener() {
            public void actionPerformed(final ActionEvent arg0) {
                JButton newbutton = new JButton("Heeeeeeeee");
                center.add(newbutton);
                center.repaint();
            }
        });
        button.setText("Button1");
        south.add(button);
    }
}

the program can be launched, but when I click the button1, the new button does not be created, it's not appear in center panel. I try my best to find out the reason but failed, please give me a hand. Your answers are appreciated much.

[hardwired]

Code:

    center.add(newbutton);
    // After adding/removing/changing a component you must
    // tell its parent container to do a new layout. We do
    // this with the JComponent method revalidate or
    // with the older Container method validate.
    center.revalidate();
//    center.repaint();