import java.util.Vector;
import java.util.EmptyStackException;

public class Stack {

    private Vector items;

    public Stack() {
	items = new Vector(10);
    }

    public Object push(Object item) {
	items.addElement(item);
	return item;
    }

    public synchronized Object pop() {
	int len = items.size();
	Object obj = null;
	if (len == 0)
	    throw new EmptyStackException();
	obj = items.elementAt(len - 1);
	items.removeElementAt(len - 1);
	return obj;
    }

    public boolean isEmpty() {
	if (items.size() == 0)
	   return true;
	else
	   return false;
    }
}