public class QueueReferenceBased implements QueueInterface
{
    private Node lastNode;
    
    public QueueReferenceBased()
    {
        lastNode = null;
    }  // end default constructor
    
    // queue operations:
    public boolean isEmpty()
    {
        return lastNode == null;
    }  // end isEmpty
    
    public void dequeueAll()
    {
        lastNode = null;
    }  // end dequeueAll
    
    public void enqueue(Object newItem)
    {
        Node newNode = new Node(newItem);
        
        // insert the new node
        if (isEmpty())
        {
            // insertion into empty queue
            newNode.setNext(newNode);
        }
        else
        {
            // insertion into nonempty queue
            newNode.setNext(lastNode.getNext());
            lastNode.setNext(newNode);
        }  // end if
        
        lastNode = newNode;  // new node is at back
    }  // end enqueue
    
    public Object dequeue() throws QueueException
    {
        if (!isEmpty())
        {
            // 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());
            }  // end if
            return firstNode.getItem();
        }
        else
        {
            throw new QueueException("QueueException on dequeue:"
            + "queue empty");
        }  // end if
    }  // end dequeue
    
    public Object peek() throws QueueException
    {
        if (!isEmpty())
        {
            // queue is not empty; retrieve front
            Node firstNode = lastNode.getNext();
            return firstNode.getItem();
        }
        else
        {
            throw new QueueException("QueueException on peek:"
            + "queue empty");
        }  // end if
    }  // end peek
    
} // end QueueReferenceBased