/**
 * 
 * ITI 1121. Introduction to Computing II
 *
 * Stack Abstract Data Type. A Stack is a linear data structure
 * following last-in-first-out protocol, i.e. the last element added
 * onto the Stack is the first one to be removed.
 *
 * @author Marcel Turcotte, University of Ottawa
 */

public interface Stack {

    /**
     * Tests if this Stack is empty.
     *
     * @return true if this Stack is empty; and false otherwise.
     */

    public abstract boolean isEmpty();

    /**
     * Returns a reference to the top element; does not change
     * the state of this Stack.
     *
     * @return The top element of this stack without removing it.
     */

    public abstract Object peek();

    /**
     * Removes and returns the element at the top of this stack.
     *
     * @return The top element of this stack.
     */

    public abstract Object pop();

    /**
     * Puts an element onto the top of this stack.
     *
     * @param element the element be put onto the top of this stack.
     */

    public abstract void push( Object element );

}