/** The Queue interface specifies the methods for a queue data structure.
 *    - The enqueue method adds an element to the "back" of the data structure.
 *    - The dequeue method acts as follows:
 *        - If the queue is empty, an exception is thrown.
 *        - If the queue contains one element, dequeue returns that element,
 *          leaving the queue empty.
 *        - If the queue contains multiple elements, dequeue returns the
 *          element at the "front" of the queue, the one that has been there longest.
 **/
public interface Queue <T>
{
    /** Returns true if this queue is empty; false otherwise. */
    boolean isEmpty();

    /** Returns the number of elements currently in the queue.
     *    @returns the number of elements
     **/
    int size();
     
    /** Adds a specified object to the "back" of this queue.
     *    @param item - the object to add to the queue
     */
    void enqueue(T item);
     
    /** Removes the element at the "front" of this queue.
     *    @returns the returned element
     *    @throws an exception if the queue is empty
     **/
    T dequeue();
     
    /** Returns the element at the "front" of this queue, without
     *  modifying the queue.
     *    @throws an exception if the queue is empty
     **/
    T peekFront();


}