Hi all,
I am having a little problem with my relay buffer which uses flow design patterns. The problem is that when the consumer should output the value of the Element, it is printing out "The item is: null". My code is a little bit long, but hopefully you can bare with me, and help me find out why it comes out as null:
// Buffer.java
public interface Buffer extends Put, Take
{
public void put ( Element item ) ;
public Element take ( ) ;
}// DummyBuffer.java
class DummyBuffer implements Buffer
{
private Element contents ;
private boolean available = false;
public synchronized Element take( )
{
while ( !available )
{
try {
wait();
}
catch ( InterruptedException e ) { }
}
available = false ;
notifyAll( ) ;
return contents ;
}
public synchronized void put( Element element )
{
while ( available )
{
try {
wait( ) ;
}
catch ( InterruptedException e ) { }
}
contents = element ;
available = true ;
notifyAll() ;
}
}// Element.java
class Element extends Object
{
private Object element ;
public Element( )
{
super() ;
element = new String( "This is an Element" ) ;
}
public Element( Object e )
{
super() ;
element = e ;
}
public String toString()
{
return element.toString() ;
}
}// EndOfData.java
class EndOfData extends Element
{
private final String DEFAULT_MESSAGE = "TERMINATE" ;
private final String message ;
// default message version
EndOfData ( )
{
message = DEFAULT_MESSAGE ;
}
// message version
EndOfData( String message )
{
this.message = message ;
}
public String toString ()
{
return "EndOfData[" + message + "]" ;
}
}// LinearStage.java
abstract class LinearStage extends Stage
{
// 1 "take" input source
private final TakeStage in ;
// 1 "put" output source
private final PutStage out ;
public LinearStage( TakeStage in, PutStage out )
{
// Stage constructor
super() ;
this.in = in ;
this.out = out ;
}
public void run ( )
{
Element element = in.take() ;
// while not end of data retrieve more items
while ( notEndOfData( element ) )
{
Element processedElement = processData( element ) ;
out.put( processedElement ) ;
element = in.take() ;
}
// propagate the "EndOfData"
out.put( new EndOfData() ) ;
}
// Abstract methods
// used to indicate when the stage should terminate
abstract protected boolean notEndOfData( Element element ) ;
// used to ``process'' the data
abstract protected Element processData( Element element ) ;
}// Put.java
public interface Put
{
abstract public void put( Element item ) ;
}// PutStage.java
abstract public class PutStage extends Stage
implements Put
{
public PutStage( )
{
// Stage constructor
super() ;
}
}// RB_Consumer.java
class RB_Consumer extends PutStage
{
private Element item ;
public RB_Consumer( )
{
// PutStage's constructor
super() ;
}
public synchronized void put( Element item )
{
this.item = item ;
}
public void run()
{
// use `item'
System.out.println( "The item: " + item ) ;
}
}// RB_Producer.java
class RB_Producer extends Stage
{
private Put nextStage ;
public RB_Producer(Put nextStage )
{
super() ;
this.nextStage = nextStage ;
}
public void run( )
{
Element item = new Element( "An Element" ) ;
nextStage.put( item ) ;
}
}// RelayBuffer.java
public class RelayBuffer implements Runnable,
Put
{
protected Put consumer ;
protected Buffer buffer = new DummyBuffer() ;
protected Thread pusher ;
public RelayBuffer( PutStage consumer )
{
this.consumer = consumer ;
// create & start the ``pusher'' thread
pusher = new Thread(this) ;
pusher.start() ;
}
public synchronized void put( Element e )
{
buffer.put( e ) ;
}
// pusher thread's body
public void run( )
{
while ( true )
{
// retrieve item from internal buffer
Element item = buffer.take() ;
// pusher thread `pushes' data to consumer
consumer.put( item ) ;
}
}
}// RelayBufferSystem.java
class RelayBufferSystem
{
private RelayBuffer relaybuffer ;
private Stage producer ;
private PutStage consumer ;
public RelayBufferSystem( )
{
// construct system in right to left order
// first create consumer
consumer = new RB_Consumer() ;
// pass reference to consumer to relaybuffer
relaybuffer = new RelayBuffer( consumer ) ;
// pass reference to relaybuffer to producer
producer = new RB_Producer( relaybuffer ) ;
// start threads
producer.start() ;
consumer.start() ;
}
}// Stage.java
class Stage extends Thread
{
private final String Descriptor = "Flow Design Pattern: Stage" ;
public Stage( )
{
// Thread constructor
super() ;
}
public String getDescriptor()
{
return Descriptor ;
}
}// Take.java
public interface Take
{
abstract public Element take( ) ;
}abstract public class TakeStage extends Stage
implements Take
{
public TakeStage( )
{
// Stage constructor
super() ;
}
}Sorry for the long code listing, hopefully you can help me find out why the consumer is printing out null.
Thanks
