/*
 * This was used in class to discuss: "helper classes", object
 * references (pointers, or the lack thereof), linked list, garbage
 * collection.
 */
class MyNode {
    Object item;
    MyNode next;
    MyNode(Object it) {
	item = it;
	next = null;
    }
    MyNode(Object item, MyNode next) {
	this.item = item;
	this.next = next;
    }
}


public class MyStack {
    MyNode list = null;
    
    public MyStack() {}
    public void push(Object item) {
	list = new MyNode(item, list);
    }
    public Object pop() {
	Object obj = list.item;
	list = list.next;
	return obj;
    }
    public boolean empty() {
	return list == null;
    }
}