sharedcell2.java

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 // Show multiple threads modifying shared object.
 import java.text.DecimalFormat;
 import java.awt.*;
 import java.awt.event.*;
 import javax.swing.*;

 public class SharedCell extends JFrame 
 {
	 public SharedCell()
	 {
		 super( "Demonstrating Thread Synchronization" );
		 JTextArea output = new JTextArea( 20, 30 );

		 getContentPane().add( new JScrollPane( output ) );
		 setSize( 500, 500 );
		 show();

		 // set up threads and start threads
		 HoldIntegerSynchronized h = new HoldIntegerSynchronized( output );
		 ProduceInteger p = new ProduceInteger( h, output );
		 ConsumeInteger c = new ConsumeInteger( h, output );

		 p.start();
		 c.start();
	 }

	 public static void main( String args[] )
	 {
		 SharedCell app = new SharedCell();
		 app.addWindowListener( new WindowAdapter() 
		 {
			 public void windowClosing( WindowEvent e )
			 {
				 System.exit( 0 );
			 }
		 } );
	 }	
 }

 // Definition of threaded class ProduceInteger
 import javax.swing.JTextArea;

 public class ProduceInteger extends Thread 
 {
	 private HoldIntegerSynchronized pHold;
	 private JTextArea output;

	 public ProduceInteger( HoldIntegerSynchronized h, JTextArea o )
	 {
		 super( "ProduceInteger" );
		 pHold = h;
		 output = o;
	 }

	 public void run()
	 {
		 for ( int count = 1; count <= 10; count++ ) 
		 {
			 // sleep for a random interval
			 // Note: Interval shortened purposely to fill buffer
			 try 
			 {
				 Thread.sleep( (int) ( Math.random() * 500 ) );
			 }
			 catch( InterruptedException e ) 
			 {
				 System.err.println( e.toString() );
			 }

			 pHold.setSharedInt( count );
		 }

		 output.append( "\n" + getName() + " finished producing values" + "\nTerminating " + getName() + "\n" );
	 }
 }

 // Definition of threaded class ConsumeInteger
 import javax.swing.JTextArea;

 public class ConsumeInteger extends Thread 
 {
	 private HoldIntegerSynchronized cHold;
	 private JTextArea output;

	 public ConsumeInteger( HoldIntegerSynchronized h, JTextArea o )
	 {
		 super( "ConsumeInteger" );
		 cHold = h;
		 output = o;
	 }

	 public void run()
	 {
		 int val, sum = 0;

		 do 
		 {
			 // sleep for a random interval
			 try 
			 {
				 Thread.sleep( (int) ( Math.random() * 3000 ) );
			 }
			 catch( InterruptedException e ) 
 			 {
				 System.err.println( e.toString() );
			 }

			 val = cHold.getSharedInt();
			 sum += val;
		 } 
		 while ( val != 10 );

		 output.append( "\n" + getName() + " retrieved values totaling: " + sum + "\nTerminating " + getName() + "\n" );
	 }
 }

 // Definition of class HoldIntegerSynchronized that
 // uses thread synchronization to ensure that both
 // threads access sharedInt at the proper times.
 import javax.swing.JTextArea;
 import java.text.DecimalFormat;

 public class HoldIntegerSynchronized 
 {
	 private int sharedInt[] = { -1, -1, -1, -1, -1 };
	 private boolean writeable = true;
	 private boolean readable = false;
	 private int readLoc = 0, writeLoc = 0;
	 private JTextArea output;

	 public HoldIntegerSynchronized( JTextArea o )
	 {
		 output = o;
	 }

	 public synchronized void setSharedInt( int val )
	 {
		 while ( !writeable ) 
		 {
			 try 
			 {
				 output.append( " WAITING TO PRODUCE " + val );
				 wait();
			 }
			 catch ( InterruptedException e ) 
			 {
				 System.err.println( e.toString() );
			 }
		 }
	
		 sharedInt[ writeLoc ] = val;
		 readable = true;

		 output.append( "\nProduced " + val + " into cell " + writeLoc );

		 writeLoc = ( writeLoc + 1 ) % 5;

		 output.append( "\twrite " + writeLoc + "\tread " + readLoc);
		 displayBuffer( output, sharedInt );

		 if ( writeLoc == readLoc ) 
		 {
			 writeable = false;
			 output.append( "\nBUFFER FULL" );
		 }

		 notify();
	 }

	 public synchronized int getSharedInt()
	 {
		 int val;

		 while ( !readable ) 
		 {
			 try 
			 {
				 output.append( " WAITING TO CONSUME" );
				 wait();
			 }
			 catch ( InterruptedException e ) 
			 {
				 System.err.println( e.toString() );
			 }
		 }

		 writeable = true;
		 val = sharedInt[ readLoc ];

		 output.append( "\nConsumed " + val + " from cell " + readLoc );

		 readLoc = ( readLoc + 1 ) % 5;

		 output.append( "\twrite " + writeLoc + "\tread " + readLoc );
		 displayBuffer( output, sharedInt );

		 if ( readLoc == writeLoc ) 
		 {
			 readable = false;
			 output.append( "\nBUFFER EMPTY" );
		 }

		 notify();
		 return val;
	 }

	 public void displayBuffer( JTextArea out, int buf[] )
	 {
		 DecimalFormat formatNumber = new DecimalFormat( " #;-#" );
		 output.append( "\tbuffer: " );

		 for ( int i = 0; i < buf.length; i++ )
			 out.append( " " + formatNumber.format( buf[ i ] ));
	 }
 }