ActionListener Problem - Event not triggering properly

Question

Hello,
I have slight problem ith action listeners. Below is an exercise from a book on java i'm reading. I have constructed rectangle with 3 circles inside.
When the button in one panel is pushed the colors of these cicles should change from green,black,black to black,yellow,black to black,black,red and start over.
When the button is clicked the event isn't triggered. However when I push the button and click the frame of the window the colors change.
I would be grateful if anyone could explain why this is happening?
// Zepang
import javax.swing.*;
import java.awt.*;
public class Pp415
     public static void main(String [] args)
          JFrame frame = new JFrame("Traffic Lights");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          Prime panel = new Prime();
          frame.getContentPane().add(panel);
          frame.pack();
          frame.setVisible(true);
     JButton lightButton = new JButton("Change the Lights!");
     lightButton.addActionListener(this);
     buttonLight.add(lightButton);
        add(buttonLight);
     add(light);
     int color = 0;
     public void actionPerformed (ActionEvent event)
          Color g = light.getGreenLight();
          Color y=  light.getYellowLight();
          Color r=  light.getRedLight();
          if (g.equals(Color.green))
               light.setGreenLight(Color.black);
               light.setYellowLight(Color.yellow);
          if (y.equals(Color.yellow))
               light.setYellowLight(Color.black);
               light.setRedLight(Color.red);
          if (r.equals(Color.red))
               light.setRedLight(Color.black);
               light.setGreenLight(Color.green);
import javax.swing.*;
import java.awt.*;
class TrafficLight extends JPanel
     Color redLight = Color.black;
     Color yellowLight = Color.black;
     Color greenLight = Color.green;
public TrafficLight()
     setBackground(Color.black);
     setPreferredSize(new Dimension (200,300));
  public void setRedLight(Color c)
     redLight = c;
  public void setYellowLight(Color c)
     yellowLight = c;
  public void setGreenLight(Color c)
     greenLight = c;
  public Color getRedLight()
  return redLight;
  public Color getGreenLight()
  return greenLight;
  public Color getYellowLight()
  return yellowLight;
  public void paintComponent(Graphics page)
     final int C = 25;
     page.setColor(Color.blue);
     page.fillRect(C, C, 100, 250);
     page.setColor(greenLight);
     page.fillOval(C+10,C+5,80,80);
     page.setColor(yellowLight);
     page.fillOval(C+10,C+90,80,80);
     page.setColor(redLight);
     page.fillOval(C+10,C+170,80,80);
}Edited by: Zepang on Dec 4, 2008 4:24 PM
Edited by: Zepang on Dec 4, 2008 4:25 PM

Answer 1

I don't in general do GUI stuff. But I can see for sure that you're never telling the system that it needs to repaint when you change state. That's why it doesn't show up until you cause an external event causing it to repaint itself, such as resizing the frame or dragging another window across the window.