Buttons and Event Handlers

Hi,

I am a newbie in Java. While learning from the Horstmann I have
modified a little example from the book. The problem is that the
buttons it creates are never shown.

Please, would someone explain what I am missing? The code follows.
Thanks in advance to everyone who will reply.

fabio

ButtonTest.java

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

public class ButtonTest
{
    public static void main( String[] args )
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                ButtonFrame frame = new ButtonFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }
}

@SuppressWarnings("serial")
class ButtonFrame extends JFrame
{
    public ButtonFrame()
    {
        setTitle("ButtonTest");
        setSize(300, 200);
        buttonPanel = new JPanel();
        makeButton("Red", Color.RED);
        makeButton("Green", Color.GREEN);
        makeButton("Blue", Color.BLUE);
    }

    private void makeButton(String name, final Color backgroundColor)
    {
        JButton button = new JButton(name);
        buttonPanel.add(button);
        button.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                buttonPanel.setBackground(backgroundColor);
            }

        });

    }

    private JPanel buttonPanel;
}