queue2_enqueue_dequeue_isFull_isEmpty

public class Queue {
	private LinkedList list;
	
	// Queue constructor
	public Queue()
	{
		// Create a new LinkedList.
		list = new LinkedList();
	}

	public boolean isEmpty()
	// Post: Returns true if the queue is empty. Otherwise, false.
	{
		return (list.size() == 0);
	}

	public void enqueue(Object item)
	// Post: An item is added to the back of the queue.
	{
		// Append the item to the end of our linked list.
		list.add(item);
	}

	public Object dequeue()
	// Pre: this.isEmpty() == false
	// Post: The item at the front of the queue is returned and 
	//         deleted from the queue. Returns null if precondition
	//         not met.
	{
		// Store a reference to the item at the front of the queue
		//   so that it does not get garbage collected when we 
		//   remove it from the list.
		// Note: list.get(...) returns null if item not found at
		//   specified index. See postcondition.
		Object item = list.get(1);
		// Remove the item from the list.
		// My implementation of the linked list is based on the
		//   J2SE API reference. In both, elements start at 1,
		//   unlike arrays which start at 0.
		list.remove(1);
		
		// Return the item
		return item;
	}

	public Object peek()
	// Pre: this.isEmpty() == false
	// Post: The item at the front of the queue is returned and 
	//         deleted from the queue. Returns null if precondition
	//         not met.
	{
		// This method is very similar to dequeue().
		// See Queue.dequeue() for comments.
		return list.get(1);
	}
}