package rebelsky.linear;

/**
 * An implementation of queues using linked nodes.  
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of October 2004.
 */
public class LinkedQueue
	implements Queue
{
// +--------+--------------------------------------------------
// | Fields |
// +--------+

	/** The "last" thing. */
	QueueNode back;

	/** The "first" thing. */
	QueueNode front;

// +--------------+--------------------------------------------
// | Constructors |
// +--------------+
	
	public LinkedQueue()
	{
		this.front = null;
		this.back = null;
	} // LinkedQueue()

// +---------+-------------------------------------------------
// | Methods |
// +---------+

	public void put(Object addMe)
	{
		// Build a new QueueNode
		QueueNode newEnd = new QueueNode(addMe, null);
		// Sanity check!  Is the list empty?
		if (this.back == null) {
			this.back = newEnd;
			this.front = newEnd;
		}
		else {
  		  // Make the back QueueNode refer to that as "rest"
		  // The current back's next element should be newEnd
		  this.back.next = newEnd;
  		  // * Update back
		  this.back = this.back.next;
		}
	} // put(Object)

	public Object get()
	{
		// Get the value stored in the front QueueNode
		Object value = this.front.data;
		
  		// Move front to the next QueueNode
		this.front = this.front.next;
		
		// Sanity check!  Did we just make the queue
		// empty?
		if (this.front == null)
			this.back = null;

		// That's it
		return value;
	} // get()

	public Object peek()
	{
		return this.front.data;
	} // peek()

	public boolean isEmpty()
	{
		return this.back == null;
	} // isEmpty()

} // class LinkedQueue