ButtonPanel.java

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

public class ButtonPanel extends JPanel implements ActionListener{

    private JButton yellowButton;
    private JButton blueButton;
    private JButton redButton; 

    public ButtonPanel(){
        yellowButton = new JButton("Yellow");
        blueButton = new JButton("Blue");
        redButton = new JButton("Red");

        yellowButton.setActionCommand("YELLOW");
        blueButton.setActionCommand("BLUE");
        redButton.setActionCommand("RED");

        add(yellowButton);
        add(blueButton);
        add(redButton);
    }
        
    public void actionPerformed(ActionEvent evt){
        Color color = getBackground();
        String cmd = evt.getActionCommand();   // Use ActionCommand to
                                               //  determine what to do

        if (cmd.equals("YELLOW")) color = Color.yellow;
        else if (cmd.equals("BLUE")) color = Color.blue;
        else if (cmd.equals("RED")) color = Color.red;

        setBackground(color);
        repaint();
    }

    public void addListener(ActionListener o){
        yellowButton.addActionListener(o);     // Add a commmon listener
        blueButton.addActionListener(o);       //   for all buttons in
        redButton.addActionListener(o);        //   this panel
    }
}