Java Queue Data Structure

Queue.java

/**
 * Queue
 * 
 * @author JJ Ford
 *
 */
public class Queue {

	private int size;
	private Node front, back;
	
	/**
	 * Node Structure
	 *
	 */
	private class Node {
		private Object item;
		private Node next;
		
		public Node(Object item, Node next) {
			this.item = item;
			this.next = next;
		}
	}
	
	/**
	 * Constructor
	 */
	public Queue() {
		front = back = null;
		size = 0;
	}
	
	/**
	 * Adds and item to the queue.
	 * 
	 * @param item The item to add to the queue.
	 */
	public void enqueue(Object item) {
		if(front == null) {
			front = back = new Node(item, null);
		} else {
			back.next = new Node(item, null);
			back = back.next;
		}
		++size;
	}
	
	/**
	 * Removes and item from the queue.
	 * 
	 * @return The item removed from the queue, null if queue is emptry.
	 */
	public Object dequeue() {
		Node dequeue;
		if(front == null) {
			return null;
		}
		--size;
		if(front == back) {
			dequeue = front;
			front = back = null;
			return dequeue.item;
		}
		dequeue = front;
		front = front.next;
		return dequeue.item;
	}
	
	/**
	 * Returns the front item in the queue but does not remove it.
	 * 
	 * @return The front item in the queue, null if queue is empty.
	 */
	public Object front() {
		if(front == null) {
			return null;
		}
		return front.item;
	}
	
	/**
	 * @return The size of the queue
	 */
	public int size() {
		return size;
	}
}