public static void main(String[] args) {
   Boss Boss = new Boss("老板", "在办公室");
   Guard guard = new Guard("前台");
   Boss.addObserver(guard);
   Boss.getState();
   Boss.setState("离开了");
   Boss.setState("回来了");
 }
 @Override
 public void update(Observable o, Object arg) {
   Boss boss = (Boss) o;
   System.out.println(this.getName() + "报告" + boss.getName() + boss.getState());
 }