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观察者模式的Java实现
The Observer Pattern defines a one-to-many
dependency between objects so that when one
object changes state, all of its dependents are
notified and updated automatically.
Java 的实现方式：
第一个类继承自java.util.Observable,这个类是被观察者要实现的类。实际应用中如天气预报的数据源类、监控中的数据汇总类等。这个基类有几个方法接口：
public synchronized void addObserver(Observer o)
public synchronized void deleteObserver(Observer o)
public void notifyObservers()
public void notifyObservers(Object arg)
public synchronized void deleteObservers()
protected synchronized void setChanged()
第二个类是观察者类java.util.Observer。 他只有一个方法: update
这里有几个很重要的概念需要记住：Observable类所处的角色应该是一个看板一样，想要被更新的对象要在他这里被注册（注意在整个程序中应该保持这个Observable对象的惟一性，而且有哪些观察者来订阅它完全是由主程序决定的。）Observable和Observer所共同关心的数据源应该是被独立出来的也就是update, notify中提到的arg对象
package com.ctrip.pattern.Observer; import java.util.Observable; import java.util.Observer; /** * Created by ygshen on 2015/8/6. */ public class WeatherDataSubject extends Observable { public WeatherDataSubject(){ } public void Trigger(Object arg){ setChanged(); notifyObservers(arg); } @Override protected synchronized void setChanged() { super.setChanged(); } @Override public void notifyObservers() { super.notifyObservers(); } @Override public synchronized void addObserver(Observer o) { super.addObserver(o); } @Override public synchronized void deleteObserver(Observer o) { super.deleteObserver(o); } @Override public void notifyObservers(Object arg) { super.notifyObservers(arg); } @Override public synchronized void deleteObservers() { super.deleteObservers(); } }
package com.ctrip.pattern.Observer; import java.util.Observable; import java.util.Observer; /** * Created by ygshen on 2015/8/6. */ public class WeatherDataObserver implements Observer { private Observable _observable; public WeatherDataObserver(Observable subject) { _observable=subject; subject.addObserver(this); } @Override public void update(Observable o, Object arg) { if(o instanceof WeatherDataSubject){ WeatherData data = (WeatherData)arg; System.out.print("Temprature"+data.get_temp()+"; humidity:"+data.get_humidity()); } } }
package com.ctrip.pattern.Observer; /** * Created by ygshen on 2015/8/6. */ public class WeatherData { private int _temp; private int _humidity; public int get_temp() { return _temp; } public void set_temp(int _temp) { this._temp = _temp; } public int get_humidity() { return _humidity; } public void set_humidity(int _humidity) { this._humidity = _humidity; } }
主程序主要负责：Observerable对象的一致性、哪些观察者要注册到被观察者中、被观察者何时触发观察者事件
import com.ctrip.pattern.Observer.WeatherData; import com.ctrip.pattern.Observer.WeatherDataObserver; import com.ctrip.pattern.Observer.WeatherDataSubject; /** * Created by ygshen on 2015/8/6. */ public class MainClass { public static void main(String[] args){ WeatherDataSubject sub=new WeatherDataSubject(); WeatherDataObserver bserver=new WeatherDataObserver(sub); GetSubjectorAndObservers(sub,bserver); WeatherData data = new WeatherData(); data.set_humidity(123); data.set_temp(321); sub.Trigger(data); } private static void GetSubjectorAndObservers(WeatherDataSubject sub,WeatherDataObserver observer){ sub = new WeatherDataSubject(); observer = new WeatherDataObserver(sub); } }
观察者模式的NET实现。
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace Test.Library { public class Subjector: IObservable<ObservableItem> { private List<IObserver<ObservableItem>> _observers=new List<IObserver<ObservableItem>>(); public IDisposable Subscribe(IObserver<ObservableItem> observer) { if (!_observers.Contains(observer)) { _observers.Add(observer); } return new Unsubscriber(_observers, observer); } public void Trigger(ObservableItem item) { foreach (var i in _observers) { i.OnNext(item); } } } public class Unsubscriber: IDisposable { private List<IObserver<ObservableItem>> _observers; private IObserver<ObservableItem> _observer; public Unsubscriber(List<IObserver<ObservableItem>> observers, IObserver<ObservableItem> observer) { _observers = observers; _observer = observer; } public void Dispose() { throw new NotImplementedException(); } } public class ObservableItem{ } }
Observer:
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace Test.Library { public class Observer : IObserver<ObservableItem> { public void OnCompleted() { throw new NotImplementedException(); } public void OnError(Exception error) { throw new NotImplementedException(); } public void OnNext(ObservableItem value) { Console.WriteLine("Observer is triggered"); } } }
public class Monitor { private void GetSubjectorAndObservers(out Subjector s, out Observer o) { s = new Subjector(); o = new Observer(); s.Subscribe(o); } public void DoMonitor(Action<Subjector> action) { Subjector s; Observer o; GetSubjectorAndObservers(out s, out o); s.Trigger(new ObservableItem()); action(s); } } static void Main(string[] args) { Monitor mon = new Monitor(); mon.DoMonitor((observer) => { Console.WriteLine("Hello world"); }); }
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原文地址：http://www.cnblogs.com/ygshen/p/4707144.html
