java观察者模式实现和java观察者模式演化

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * 观察者模式中用到了回调:
 * A. 观察者将自己注册到被观察者的监听者列表，且观察者类自身提供了一个回调函数
 * B. 被观察者（Observable或Subject）维护观察者列表，并且可以注册和解注册观察者
 * C. 一旦被观察者状态发生改变，它可以调用notifyObservers()，这个方法将遍历观察者列表并逐个调用
观察者提供的回调函数
 * @author will
 *
 */
public class SimpleObserverPattern {

 public static void main(String[] args) {
  SimpleObserverPattern sop = new SimpleObserverPattern();

  List observers = new ArrayList ();
  IObserver observerA = sop.new Observer("ObserverA");
  IObserver observerB = sop.new Observer("ObserverB");
  observers.add(observerA);
  observers.add(observerB);

  IObservable observable = sop.new Observable(observers);
  observable.registerObserver(sop.new Observer("ObserverC"));

  observable.changeState();
  observable.close();
 }

 // 被观察者，有的地方叫Subject
 interface IObservable {
  void registerObserver(IObserver observer);
  void unregisterObserver(IObserver observer);
  void notifyObservers();
  String getState();
  void changeState();
  void close();
 }

 class Observable implements IObservable {

  private static final String NEW = "New";
  private static final String CHANGED = "Changed";
  private static final String CLOSED = "Closed";

  private String state;
  private List observers;

  public Observable() {
   this(null);
  }

  public Observable(List observers) {
   if(observers == null) {
    observers = new ArrayList ();
   }
    this.observers = Collections.synchronizedList(observers);
    this.state = NEW;
  }

  @Override
  public void registerObserver(IObserver observer) {
   observers.add(observer);
  }

  @Override
  public void unregisterObserver(IObserver observer) {
   observers.remove(observer);
  }

  @Override
  public void notifyObservers() {
   Iterator iter = observers.iterator();
   while(iter.hasNext()) {
    iter.next().update(this);
   }
  }

  @Override
  public String getState() {
   return state;
  }

  @Override
  public void changeState() {
   this.state = CHANGED;
   notifyObservers();
  }

  @Override
  public void close() {
   this.state = CLOSED;
   notifyObservers();
  }
 }

 interface IObserver {
  void update(IObservable observalbe);
 }

 class Observer implements IObserver {

  private String name;

  public Observer(String name) {
   this.name = name;
  }

  @Override
  public void update(IObservable observalbe) {
   System.out.println(
     String.format("%s receive observalbe's change, current observalbe's state is %s",
        name, observalbe.getState()));
  }

 }

}