package DataStructures;

import java.util.NoSuchElementException;

/**
 * A linked list implementation of a stack
 * @author Peter Williams
 */

public class StackList implements Stack {

    private ListNode top;

    public StackList() {
        top = null; 
    }

    public boolean isEmpty() {
        return top == null;
    }
  
    public void push(Object item) {
        top = new ListNode(item, top);
    }
  
    public Object pop() {
        if (top == null) {
            throw new NoSuchElementException();
        } else {
            Object item = top.data;
            top = top.next;
            return item;
        }
    }
  
}