ActionListener listener = ...;
JButton button = new JButton("OK");
button.addActionListener(listener);

class MyListener implements ActionListener
{
 ...;
 public void actionPerformed(ActionEvent event)
 {
   //reaction to button click goes here
 }
}

JButton yellowButton = new JButton("Yellow");
JButton blueButton = new JButton(new ImageIcon("blue-ball.gif"));

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

buttonPanel.add(yellowButton);
buttonPanel.add(blueButton);
buttonPanel.add(redButton);

class ColorAction implements ActionListener
{
  public ColorAction(Color c)
  {
   backgroundColor = c;
  }
  public void actionPerformed(actionEvent event)
  {
   //set panel background color
   }
   private Color backgroundColor;
}

ColorAction yelloAction = new ColorAction(Color.YELLOW);
ColorAction blueAction = new ColorAction(Color.BLUE);
ColorAction redAction = new ColorAction(Color.RED);

yellowButton.addActionListener(yellowAction);
blueButton.addActionListener(blueAction);
redButton.addActionListener(redAction);

class ButtonFrame extends JFrame
{
 ...
 private class ColorAction implents ActionListener
 {
  ...
  public void actionPerformed(ActionEvent event)
  {
    buttonPanel.setBackground(backgroundColor);
  }
  private Color backgroundColor;
  }
  private Jpanel buttonPanel; 
}