/* Stack.java
** An instance of a class that implements this interface represents a stack, 
** which is a container having a last-in-first-out (LIFO) arrival/departure
** pattern.
** Author: R. McCloskey
*/

public interface Stack<T> {

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

   /* Returns the number of items on the stack.
   */
   int sizeOf();

   /* Reports whether or not there are no items on the stack.
   */
   boolean isEmpty();

   /* Returns the capacity of the stack (i.e., the maximum # of items 
   ** that can occupy it at any one time).
   */
   int capacityOf();

   /* Returns (a reference to) the item at the top of the stack.
   ** pre: !isEmpty()
   */
   T topOf();


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

   /* Places (a reference to) the specified item on top of the stack.
   ** pre: sizeOf() < capacityOf()
   */
   void push( T item );

   /* Removes the item at the top of the stack and returns (a reference to) it.
   ** pre: !isEmpty()
   */
   T pop();

   /* Makes the stack empty.
   */
   void clear();

}