Queue Reference Based issued

Question

Hi all..could anyone tell me how i should fix the problem that i am struck here? I try to implemented an queue on my own. but i change sth in that queue.. i try not to use isEmpty() to keep track of the element in my queue..(it work fine if i use isEmpty()....) instead of using size() to keep track if it is an empty stack...but i got a little bit problem here..it call the exception automatically..and i am not expecting this result
=========================
javac QueueTest.java
Exit code: 0
java QueueTestThe queue is empty
0 1 2 3 4 5 6 7 8
EmptyQueueException on peek:queue empty <<- error occur here.ithould not appear.
Exit code: 0=====================
expected result
=========================
javac QueueTest.java
Exit code: 0
java QueueTestThe queue is empty
0 1 2 3 4 5 6 7 8
Exit code: 0=====================
my code is as following
QueueTest
public class QueueTest
     public static void main(String[] args)
          QueueReferenceBased aQueue = new QueueReferenceBased();
          if(aQueue.size() == 0)
          //if(aQueue.isEmpty())
               System.out.println("The queue is empty");
          for(int i=0; i < 9; i++)
               aQueue.enqueue(new Integer(i));
          try
             //while (!aQueue.isEmpty())     
             //while(aQueue.size() != 0)
             while(aQueue.size() != 0)
                  System.out.print(aQueue.peek() + " ");
                  //System.out.print(aQueue.size() );
                  aQueue.dequeue();
            // System.out.print(aQueue.size() );
          //aQueue.peek();
          catch( EmptyQueueException eqe)
               System.out.println("\n" + eqe.getMessage());
}===
QueueReferenceBased
// File: QueueReferenceBased.java
// Author: Chi Lun To (Ivan To)
// Created on: June 5, 2007
public class QueueReferenceBased implements QueueInterface
  private Node lastNode;
  private int numberOfItems = 0;
  public QueueReferenceBased()
      lastNode = null;  
  // queue operations:
  public boolean isEmpty()
    return lastNode == null;
  public int size()
       return numberOfItems;
  public void enqueue(Object newItem)
  { // insert the new node
    Node newNode = new Node(newItem);           
   // if (isEmpty())
    if(lastNode == null)
  // if(size()==0)
           // insertion into empty queue
          newNode.setNext(newNode);
    else {
          // insertion into nonempty queue
          newNode.setNext(lastNode.getNext());
           lastNode.setNext(newNode);
    lastNode = newNode;  // new node is at back
      numberOfItems++;
  public Object dequeue() throws EmptyQueueException
      // if(!isEmpty())
//if (!(size() == 0))
if(lastNode != null)
           // queue is not empty; remove front
           Node firstNode = lastNode.getNext();
           if (firstNode == lastNode)             // special case?
                    lastNode = null;                  // yes, one node in queue
          else
                    lastNode.setNext(firstNode.getNext());
                    numberOfItems--;
          return firstNode.getItem();
    else {
          throw new EmptyQueueException("EmptyQueueException on dequeue:" + "queue empty");
  }  // end dequeue
  public Object peek() throws EmptyQueueException
      if(lastNode != null)
      //if (size() != -1)
      // queue is not empty; retrieve front
      Node firstNode = lastNode.getNext();
      return firstNode.getItem();
    else {
      throw new EmptyQueueException("EmptyQueueException on peek:"+ "queue empty");
} // end QueueReferenceBased===
the code u could omit ..but just for better unstanding ..thx
node
public class Node {
  private Object item;
  private Node next;
  public Node(Object newItem) {
    item = newItem;
    next = null;
  } // end constructor
  public Node(Object newItem, Node nextNode) {
    item = newItem;
    next = nextNode;
  } // end constructor
  public void setItem(Object newItem) {
    item = newItem;
  } // end setItem
  public Object getItem() {
    return item;
  } // end getItem
  public void setNext(Node nextNode) {
    next = nextNode;
  } // end setNext
  public Node getNext() {
    return next;
  } // end getNext
} // end class Node====
QueueInterface
public interface QueueInterface
  //public boolean isEmpty() ;
  public int size();
  // Description: Determines the number of elements in a queue.
  //                    In other words, the length of a queue.
  // Precondition: None.
  // Postcondition: Returns the number of elements that are
  //                        currently in the queue.
  // Throws: None.
  public void enqueue(Object newElement);
  // Description: Adds an element at the back of a queue.
  // Precondition: None.
  // Postcondition: If the operation was successful,
  //                        newElement is at the back of the queue.
  // Throws: None.
public Object dequeue() throws EmptyQueueException;
  // Description: Retrieves and removes the front of a queue.
  // Precondition: Queue is not empty.
  // Postcondition: If the queue is not empty, the element
  //                       that was added to the queue earliest
  //                       is returned and the element is removed.
  //                       If the queue is empty, the operation
  //                       is impossible and QueueException is thrown.
  // Throws: EmptyQueueException when the queue is empty.
  public Object peek() throws EmptyQueueException;
  // Description: Retrieves the element at the front of a queue.
  // Precondition: Queue is not empty.
  // Postcondition: If the queue is not empty, the element
  //                        that was added to the queue earliest
  //                        is returned. If the queue is empty, the
  //                        operation is impossible and QueueException
  //                        is thrown.
  // Throws: EmptyQueueException when the queue is empty.
}  // end QueueInterface=====
public class EmptyQueueException extends Exception
     //Parameterized constructor
     public EmptyQueueException( String s )
          super( s ); //inherits the existing functionality of the Exception class.
}

Answer 1

i try not to use isEmpty() to keep track of the
element in my queue..(it work fine if i use
isEmpty()....) instead of using size() to keep track
if it is an empty stack... and this is a complete red herring. isEmpty() just returns size() == 0. The two are completely equivalent and there is no possibility that one worked when the other didn't.