// Fig. 15.7: RandomCharacters.java
// Demonstrating the Runnableinterface
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class RandomCharacters extends JApplet
                              implements Runnable,
                                         ActionListener {
   private String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
   private JLabel output;
   private JCheckBox checkbox;
   
   private volatile Thread thread;
   private boolean suspended;

   public void init()
   {
      Container c = getContentPane();
      c.setLayout( new GridLayout( 1, 2, 5, 5 ) );

      output = new JLabel();
      output.setBackground( Color.green );
      output.setOpaque( true );
      c.add( output );

      checkbox = new JCheckBox( "Suspended" );
      checkbox.addActionListener( this );
      c.add( checkbox );
   }

   public void start()
   {
      thread = new Thread( this );
      thread.start();
   }

   public synchronized void stop()
   {
      // stop thread every time stop is called
      // as the user browses another Web page
      thread = null;
      notifyAll();
   }

   public synchronized void actionPerformed( ActionEvent e )
   {
      suspended = !suspended;
      System.out.println( "action: " + suspended );

      output.setBackground(
         !suspended ? Color.green : Color.red );

      notifyAll();
   }

   public void run()
   {
      Thread currentThread = Thread.currentThread();
      char displayChar;

      while ( thread == currentThread ) {
         // sleep from 0 to 1 second
         try {
            Thread.sleep( (int) ( Math.random() * 1000 ) );

            synchronized( this ) {
               System.out.println( "run: " + suspended );
               while ( suspended && thread == currentThread )
                  wait();
            }
         }
         catch ( InterruptedException e ) {
            System.out.println( "sleep interrupted" );
         }
         
         displayChar = alphabet.charAt(
                          (int) ( Math.random() * 26 ) );
         output.setText( "Random character: " + displayChar );
      }

      System.out.println( "thread terminating" );
   }
}