import java.util.*;
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 esEmpty() {
    if (items.size() == 0)
      return true;
    else
      return false;
  }
  protected void finalize() throws Throwable {
    items = null;
    super.finalize();
   }
}