BELOW YOU WILL FIND THE CODE FOR THE 
Stack Interface and a class that implements that Interface
- Copy the Interface code into a new Interface
- Copy the Class code into a new Class

//=============================================================
/**
 * Interface for a Stack
 * 
 * @author Appears in Litvin's "Be Prepared"
 */

public interface Stack
{
    boolean isEmpty();
    void push(Object x);
    Object pop();
    Object peekTop();
}

//===============================================

import java.util.ArrayList;

/**
 * Implementation of a Stack using an ArrayList
 * 
 * @author Appears in Litvin's "Be Prepared"
 */
 
public class ArrayStack implements Stack
{
    private ArrayList items;
    
    // constructor
    public ArrayStack()   { items = new ArrayList();  }    
    public boolean isEmpty() { return items.size() == 0; }    
    public void push(Object obj) { items.add(obj); }
    public Object pop() { return items.remove(items.size() - 1); }
    public Object peekTop() { return items.get(items.size() -1); }
    
}