Kan nogle se fejlen i dette program med (Thread)

Når jeg kører dette program får jeg følgende :

Thread-0 insætter 890 i queue

mypackage3.QueueException: QueueException on dequeue: Queue empty
    at mypackage3.QueueArrayBased.dequeue(QueueArrayBased.java:70)
    at mypackage3.Consumer.run(Consumer.java:14)
    at java.lang.Thread.run(Thread.java:534)

Thread-1 insætter 2277 i queue
Thread-2 insætter 2444 i queue

Hvorfor er min queue empty, når det tydeligvis fremgår at den først sætter ind i queuen, før exceptioenen kommer...

Mine klasser jeg arbejder med er:

public class ThreadsApp
{
  QueueArrayBased queue = QueueArrayBased.getInstance();
  Thread prod1, prod2, prod3; 
  Thread cons1, cons2, cons3;
 
  public ThreadsApp()
  {
    prod1 = new Thread(new Producer(queue));
    prod2 = new Thread(new Producer(queue)); 
    prod3 = new Thread(new Producer(queue));
 
    cons1 = new Thread(new Consumer(queue));
    //cons2 = new Consumer(queue);
    //cons3 = new Consumer(queue);
   
    //prod1.setPriority(7);
    prod1.start();
    prod2.start();
    prod3.start();
   
    //cons1.setPriority(2);
    cons1.start();
    //cons2.start();
    //cons3.start();
  }
  public static void main(String[] args)
  {
    ThreadsApp threadsApp = new ThreadsApp();
  }
}

.......................................................

public class Producer implements Runnable
{
  QueueArrayBased queue;
  TestObjekter tob;
 
  public Producer(QueueArrayBased queue)
  {
    this.queue = queue;
  }
  public void run()
  {
    int random = (int)(Math.random()*3000);
    tob = new TestObjekter(random);
    queue.enqueue(tob);
    System.out.println(Thread.currentThread().getName()+" insætter "+tob.getTal()+" i queue");
  }
}
.............................................................

public class Consumer implements Runnable
{
  QueueArrayBased queue;
  TestObjekter tob;
   
  public Consumer(QueueArrayBased queue)
  {
    this.queue = queue;
  }
  public void run()
  {
    tob = (TestObjekter)queue.dequeue();
    System.out.println(Thread.currentThread().getName()+" henter "+tob.getTal()+" fra queue");
  }
}
...........................................................

public class QueueArrayBased implements QueueInterface
{
  private  int MAX_QUEUE = 4; // maximum size of queue
  private Object[] items;
  private int front, back, count;
  private final static QueueArrayBased queue = new QueueArrayBased();
 
  public QueueArrayBased() {
    items = new Object[MAX_QUEUE]; 
    front = 0;
    back = MAX_QUEUE-1;
    count = 0;
  }  // end default constructor

  // queue operations:
  public boolean isEmpty() {
    return count == 0;
  }  // end isEmpty

  public boolean isFull() {
    return count == MAX_QUEUE;
  }  // end isFull
 
  public synchronized void enqueue(Object newItem) {
    if (!isFull())
    {
      back = (back+1) % (MAX_QUEUE);
      items[back] = newItem;
      ++count;
      notifyAll();
    }
    else
    {
    try
    {
      wait();
    }
    catch (InterruptedException e)
    {
      System.out.println(e);
    }
      throw new QueueException("QueueException on enqueue: "
                            + "Queue full");
    }  // end if
  }  // end enqueue

  public synchronized Object dequeue() throws QueueException {
  try
  {
    if (!isEmpty())
    {
      // queue is not empty; remove front
      Object queueFront = items[front];
      front = (front+1) % (MAX_QUEUE);
      --count;
      notifyAll();
      return queueFront;
    }
    else
    {
      wait();
    }
  }
  catch (InterruptedException e)
  {
    System.out.println(e);     
  }
    throw new QueueException("QueueException on dequeue: "+"Queue empty");
} 


  public void dequeueAll()
  {
    items = new Object[MAX_QUEUE]; 
    front = 0;
    back = MAX_QUEUE-1;
    count = 0;
  }  // end dequeueAll

  public Object peek() throws QueueException {
    if (!isEmpty()) { 
      // queue is not empty; retrieve front
      return items[front];
    }
    else {
      throw new QueueException("Queue exception on peek: " +
                              "Queue empty");
    }  // end if
  }  // end peek
  public static synchronized QueueArrayBased getInstance()
  {
    return queue;
  }
} // end QueueArrayBased