观察者模式

• Observer, 对象变化，对观察者广播

• public interface Observer {
      public void update();
  }
  public class Observer1 implements Observer {
      @Override
      public void update(){}
  }
  public interface Subject{
      public void add(Observer observer);
      public void del(Observer observer);
      public void notifyObservers();
      public void operate()
  }
  public abstract class AbstractSubject implements Subject {
      private Vector<Observer> vector = new Vector<Observer>();
      @Override
      public void add(Observer observer) {
          vector.add(observer);
      }
      @Override
      public void del(Observer observer) {
          vector.remove(observer);
      }
      @Override
      public void notifyObservers(){
          Enumeration<Observer> enumo = vector.elements();
          while (enumo.hasMoreElements()) {
              enumo.nextElement().update();
          }
      }
  }
  public class MySubject extends AbstractSubject {
      @Override
      public void operate() {
          notifyObservers();
      }
  }