package queues;

import java.util.Enumeration;

/**
 * A queue implemented using arrays.
 *
 * Version 2.
 *
 * @author Alan L. Cox
 * @since 03/15/01
 */
public class ArrayVers2Queue implements IQueue {

    private int	     _firstObject = 0;
    private int	     _lastObjectPlusOne = 0;
    private Object[] _objects = new Object[1];
    private int	     _objectsQueued = 0;

    /**
     * @param object the object to enqueue
     */
    public void enqueue(Object object)
    {
	if (_objectsQueued == _objects.length) {

	    int j;

	    Object[] newObjects = new Object[2*_objects.length];

	    _lastObjectPlusOne += _objects.length;

	    for (j = _firstObject; j < _lastObjectPlusOne; j++)
		newObjects[j] = _objects[j % _objects.length];

	    _objects = newObjects;
	}
	_objects[_lastObjectPlusOne] = object;
	_objectsQueued++;
	_lastObjectPlusOne++;
	_lastObjectPlusOne %= _objects.length;
    }

    /**
     * @return the dequeued object
     */
    public Object dequeue()
    {
	if (_objectsQueued == 0)
	    throw new java.util.NoSuchElementException("The queue is empty.");

	Object object = _objects[_firstObject];
	_objectsQueued--;
	_firstObject++;
	_firstObject %= _objects.length; // Java note: the mod operator

	return object;
    }

    /**
     * @return an Enumeration of the queue.
     */
    public Enumeration enumeration()
    {
        return new Enumeration() {

	    private int _nextObject = _firstObject;

	    public boolean hasMoreElements()
	    {
		return _nextObject < _lastObjectPlusOne;
	    }

	    public Object nextElement()
	    {
		return _objects[_nextObject++];
	    }
	};
    }
}