CStack.java

import java.util.*;

class CStack implements Stack {
    LinkedList list = new LinkedList();

    public void push(Object o) {
	list.addFirst(o);
    }

    public Object pop() {
	if (!list.isEmpty())
	    return list.removeFirst();
	else
	    return null;
    }

    public boolean notEmpty() {
	return !list.isEmpty();
    }
}