//观察者，需要用到观察者模式的类需实现此接口 public interface Observer {  void update(Object... objs); } //被观察者（一个抽象类，方便扩展） public abstract class Observable {  public final ArrayList<Class<?>> obserList = new ArrayList<Class<?>>();  /** Attach Observer （通过实例注册观察者）   * <b>Notice:</b> ob can't be null ,or it will throw NullPointerException   * */  public <T> void registerObserver(T ob) {   if (ob == null) throw new NullPointerException();   this.registerObserver(ob.getClass());  }  /**   * Attach Observer（通过Class注册观察者）   * @param cls   */  public void registerObserver(Class<?> cls) {   if (cls == null) throw new NullPointerException();   synchronized(obserList) {    if (!obserList.contains(cls)) {     obserList.add(cls);    }   }  }  /** Unattach Observer （注销观察者）   * <b>Notice:</b>   * <b>It reverses with attachObserver() method</b>   * */  public <T> void unRegisterObserver(T ob) {   if (ob == null) throw new NullPointerException();   this.unRegisterObserver(ob.getClass());  }  /** Unattach Observer（注销观察者，有时候在未获取到实例使用）   * <b>Notice:</b>   * <b>It reverses with attachObserver() method</b>   * */  public void unRegisterObserver(Class<?> cls) {   if(cls == null) throw new NullPointerException();   synchronized(obserList){    Iterator<Class<?>> iterator = obserList.iterator();    while(iterator.hasNext()) {     if(iterator.next().getName().equals(cls.getName())){      iterator.remove();      break;     }    }   }  }  /** detach all observers */  public void unRegisterAll() {   synchronized(obserList) {    obserList.clear();   }  }  /** Ruturn the size of observers */  public int countObservers() {   synchronized(obserList) {    return obserList.size();   }  }  /**   * notify all observer （通知所有观察者，在子类中实现）   * @param objs   */  public abstract void notifyObservers(Object... objs);  /**   * notify one certain observer （通知某一个确定的观察者）   * @param cls   * @param objs   */  public abstract void notifyObserver(Class<?> cls, Object... objs);  /**   * notify one certain observer   * @param cls   * @param objs   */  public abstract <T> void notifyObserver(T t, Object... objs); } //目标被观察者 public class ConcreteObservable extends Observable {  private static ConcreteObservable instance = null;  private ConcreteObservable() {}  public static synchronized ConcreteObservable getInstance() {   if (instance == null) {    instance = new ConcreteObservable();   }   return instance;  }  @Override  public <T> void notifyObserver(T t, Object... objs) {   // TODO Auto-generated method stub   if (t == null) throw new NullPointerException();   this.notifyObserver(t.getClass(), objs);  }  @Override  public void notifyObservers(Object... objs) {   // TODO Auto-generated method stub   for (Class<?> cls : obserList) {    this.notifyObserver(cls, objs);   }  }  @Override  //通过java反射机制实现调用  public void notifyObserver(Class<?> cls, Object... objs) {   // TODO Auto-generated method stub   if (cls == null) throw new NullPointerException();   Method[] methods = cls.getDeclaredMethods();   for (Method method : methods) {    if (method.getName().equals("update")) {     try {      method.invoke(cls, objs);                                         break;     } catch (IllegalArgumentException e) {      // TODO Auto-generated catch block      e.printStackTrace();     } catch (IllegalAccessException e) {      // TODO Auto-generated catch block      e.printStackTrace();     } catch (InvocationTargetException e) {      // TODO Auto-generated catch block      e.printStackTrace();     }    }   }  } } //使用 (实现Observer接口） public class Text extends Activity implements Observer {    public void onCreate(...) {        ConcreteObservable.getInstance().registerObserver(Text.class);        ....    }    //实现接口处理    public void update(Object... objs) {        // 做操作，比如更新数据，更新UI等    } }