/* An instance of a class that implements this interface represents a queue.
*/
public interface Queue<T> {

   // observers
   // ---------

   /* Returns the number of elements in this queue.
   */
   int sizeOf();

   /* Reports whether or not there are no elements in this queue.
   */
   boolean isEmpty();

   /* Returns the item at the front of this queue.
   ** pre: !isEmpty()
   */
   T frontOf();


   // mutators
   // --------

   /* Removes the item at the front of this queue.
   ** pre: !isEmpty()
   */
   void dequeue();

   /* Places the specified item at the rear of this queue.
   */
   void enqueue(T item);

}