Source Code : The TrafficLight Component

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The TrafficLight Component

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.beans.PropertyEditorSupport;
import java.beans.SimpleBeanInfo;
import java.util.TooManyListenersException;
import java.util.Vector;

import javax.swing.JComponent;

public class TrafficLight extends JComponent {

  public static String STATE_RED = "RED";

  public static String STATE_YELLOW = "YELLOW";

  public static String STATE_GREEN = "GREEN";

  private static int DELAY = 3000;

  private String defaultLightState;

  private String currentLightState;

  private boolean debug;

  private Thread runner;

  private transient ActionListener listener;

  public TrafficLight() {
    defaultLightState = currentLightState = STATE_RED;
    setPreferredSize(new Dimension(100, 200));
  }

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    // Paint the outline of the traffic light
    g.setColor(Color.white);
    g.fillRect(2, 2, 96, 196);
    // Debug
    if (debug) {
      System.out.println("Current light state is: " + currentLightState);
    }
    // Which light is on?
    if (currentLightState.equals(STATE_RED)) {
      g.setColor(Color.red);
      g.fillOval(30, 30, 40, 40);
    } else if (currentLightState.equals(STATE_YELLOW)) {
      g.setColor(Color.yellow);
      g.fillOval(30, 80, 40, 40);
    } else if (currentLightState.equals(STATE_GREEN)) {
      g.setColor(Color.green);
      g.fillOval(30, 130, 40, 40);
    }
  }

  public String getCurrentLightState() {
    return currentLightState;
  }

  public void setCurrentLightState(String currentLightState) {
    this.currentLightState = currentLightState;
    if (currentLightState != STATE_YELLOW) {
      if (debug) {
        System.out.println("Firing action event");
      }
      ActionEvent ae = new ActionEvent(this,
          ActionEvent.ACTION_PERFORMED, currentLightState);
      fireActionPerformed(ae);
    }
    repaint();
  }

  public void setDefaultLightState(String defaultLightState) {
    this.defaultLightState = defaultLightState;
    currentLightState = defaultLightState;
    repaint();
  }

  public String getDefaultLightState() {
    return defaultLightState;
  }

  public void setDebug(boolean debug) {
    this.debug = debug;
  }

  public boolean isDebug() {
    return debug;
  }

  public void initiate() {
    if (debug) {
      System.out.println("Initiate traffic light cycle!");
    }
    startCycle();
  }

  private void startCycle() {
    if (runner == null) {
      Runnable runnable = new Runnable() {
        public void run() {
          if (debug) {
            System.out.println("Started cycle");
          }
          while (runner != null) {
            try {
              Thread.sleep(DELAY);
            } catch (InterruptedException e) {
            }
            if (currentLightState.equals(STATE_RED)) {
              setCurrentLightState(STATE_GREEN);
            } else if (currentLightState.equals(STATE_GREEN)) {
              setCurrentLightState(STATE_YELLOW);
            } else {
              setCurrentLightState(STATE_RED);
            }
            if (currentLightState.equals(defaultLightState)) {
              runner = null;
            }
          }
        }
      };
      runner = new Thread(runnable);
      runner.start();
    }
  }

  public void lightChange(ActionEvent x) {
    String command = x.getActionCommand();
    if (debug) {
      System.out.println("Received event from traffic light: "
          + defaultLightState + " command: go to " + command);
    }

    if (command.equals(STATE_RED)) {
      if (!currentLightState.equals(STATE_GREEN)) {

        currentLightState = STATE_GREEN;
        repaint();
      }
    } else if (command.equals(STATE_GREEN)) {
      if (!currentLightState.equals(STATE_RED)) {
        currentLightState = STATE_YELLOW;
        repaint();
        try {
          Thread.sleep(DELAY);
        } catch (InterruptedException e) {
        }
        currentLightState = STATE_RED;
        repaint();
      }
    }
  }

  public synchronized void removeActionListener(ActionListener l) {
    if (debug) {
      System.out.println("Deregistering listener");
    }
    if (listener == l) {
      listener = null;
    }
  }

  public synchronized void addActionListener(ActionListener l)
      throws TooManyListenersException {
    if (debug) {
      System.out.println("Registering listener");
    }
    if (listener == null) {
      listener = l;
    } else {
      throw new TooManyListenersException();
    }
  }

  protected void fireActionPerformed(ActionEvent e) {
    if (debug) {
      System.out.println("Firing action event");
    }
    if (listener != null) {
      listener.actionPerformed(e);
    }
  }
}

class LightColorEditor extends PropertyEditorSupport {
  public String[] getTags() {
    String values[] = { TrafficLight.STATE_RED, TrafficLight.STATE_YELLOW,
        TrafficLight.STATE_GREEN };
    return values;
  }
}

class TrafficLightBeanInfo extends SimpleBeanInfo {
  public PropertyDescriptor[] getPropertyDescriptors() {
    try {
      PropertyDescriptor pd1 = new PropertyDescriptor("debug",
          TrafficLight.class);
      PropertyDescriptor pd2 = new PropertyDescriptor(
          "defaultLightState", TrafficLight.class);
      pd2.setPropertyEditorClass(LightColorEditor.class);
      PropertyDescriptor result[] = { pd1, pd2 };
      return result;
    } catch (IntrospectionException e) {
      System.err.println("Unexpected exception: " + e);
      return null;
    }
  }
}

class MyBean {
  private transient Vector actionListeners;

  public synchronized void removeActionListener(ActionListener l) {
    if (actionListeners != null && actionListeners.contains(l)) {
      Vector v = (Vector) actionListeners.clone();
      v.removeElement(l);
      actionListeners = v;
    }
  }

  public synchronized void addActionListener(ActionListener l) {
    Vector v = (actionListeners == null) ? new Vector(2)
        : (Vector) actionListeners.clone();
    if (!v.contains(l)) {
      v.addElement(l);
      actionListeners = v;
    }
  }

  protected void fireActionPerformed(ActionEvent e) {
    if (actionListeners != null) {
      Vector listeners = actionListeners;
      int count = listeners.size();
      for (int i = 0; i < count; i++) {
        ((ActionListener) listeners.elementAt(i)).actionPerformed(e);
      }
    }
  }
}
           
       

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