/**
 * A Stack (of Object objects)
 *
 * This implementation uses linked memory
 *
 * @version 1.0
 * @author  Prof. David Bernstein, James Madison University
 */
public class Stack
{
    private Node top;


    /**
     * Construct a new (empty) Stack
     */
	  public Stack()
     {
			top = null;
     }


    /**
     * Pop an Object off of the top of this Stack
     *
     * @return  The Object on the top of this Stack
     */
     public Object pop()
     {
			Object  value;
	
			if (top != null) 
         {
	   		value = top.value;
	    		top = top.next;
			} 
			else
			{
	    		value = null;
			}

		return value;
    } // end pop


    /**
     * Push an Object onto the top of this Stack
     *
     * @param first   The Object to push
     */
     public void push(Object first)
     {
			Node temp;

			temp = new Node();

			temp.value = first;
			temp.next = top;

			top = temp;
     } // end push
} // end Stack