Stack.java

//package org.example;

/**
* Stack is an interface for stack management operations (ADT)
*   A collection of elements inserted and removed using the last-in first-out policy.
*   This interface differs from java.util.Stack.
*
* From Goodrich, Tamassia & Goldsasser
* 
* @author      Francois Major
* @version     %I%, %G%
* @since       1.0
*/
public interface Stack<E> {
    public int     size();         // return the number of elements in the stack
    public boolean isEmpty();      // return true if the stack is empty, false otherwise
    public void    push( E e );    // insert element e at the top of the stack
    public E       top();          // return the element at the top of the stack, null if empty
    public E       pop();          // remove and return the element at the top of the stack, null if empty
}