Demonstrating the runnable interface

  import java.awt.*;

 import java.awt.event.*;

 import javax.swing.*;

 public class RandomCharacters extends JApplet implements Runnable, ActionListener 

 {

private String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

private JLabel outputs[];

private JCheckBox checkboxes[];

private final static int SIZE = 3;

private Thread threads[];

private boolean suspended[];

public void init()

{

outputs = new JLabel[ SIZE ];

checkboxes = new JCheckBox[ SIZE ];

threads = new Thread[ SIZE ];

suspended = new boolean[ SIZE ];

Container c = getContentPane();

c.setLayout( new GridLayout( SIZE, 2, 5, 5 ) );

for ( int i = 0; i < SIZE; i++ ) 

{

outputs[ i ] = new JLabel();

outputs[ i ].setBackground( Color.green );

outputs[ i ].setOpaque( true );

c.add( outputs[ i ] );

checkboxes[ i ] = new JCheckBox( "Suspended" );

checkboxes[ i ].addActionListener( this );

c.add( checkboxes[ i ] );

}

}

public void start()

{

// create threads and start every time start is called

for ( int i = 0; i < threads.length; i++ ) 

{

threads[ i ] = new Thread( this, "Thread " + (i + 1) );

threads[ i ].start();

}

}

public void run()

{

Thread currentThread = Thread.currentThread();

int index = getIndex( currentThread );

char displayChar;

while ( threads[ index ] == currentThread ) 

{

// sleep from 0 to 1 second

try 

{

Thread.sleep( (int) ( Math.random() * 1000 ) );

synchronized( this ) 

{

while ( suspended[ index ] && threads[ index ] == currentThread )

wait();

}

}

catch ( InterruptedException e ) 

{

System.err.println( "sleep interrupted" );

}

displayChar = alphabet.charAt( (int) ( Math.random() * 26 ) );

outputs[ index ].setText( currentThread.getName() +

": " + displayChar );

}

System.err.println( currentThread.getName() + " terminating" );

}

private int getIndex( Thread current )

{

for ( int i = 0; i < threads.length; i++ )

if ( current == threads[ i ] )

return i;

return -1;

}

public synchronized void stop()

{

// stop threads every time stop is called

// as the user browses another Web page

for ( int i = 0; i < threads.length; i++ )

threads[ i ] = null;

notifyAll();

}

public synchronized void actionPerformed( ActionEvent e )

{

for ( int i = 0; i < checkboxes.length; i++ ) 

{

if ( e.getSource() == checkboxes[ i ] ) 

{

suspended[ i ] = !suspended[ i ];

outputs[ i ].setBackground( !suspended[ i ] ? Color.green : Color.red );

if ( !suspended[ i ] )

notify();

return;

}

}

}

 }