java观察者_Java中的观察者模式
让一个类能够被观察，则该类需要继承java.util.Observable类。
要让一个类成为观察者，则该类需要实现java.util.Observable接口。
让观察者和被观察者建立联系通过Observable的addObserver(Object obj)方法。
让被观察者通知观察者，通过Observable类中的setChanged()和notifyObservers(Object obj)方法。
下面的例子定义了一个售房中心类和一个卖家类。售房中心为被观察者，买房者为观察者。售房中心房价发生变化，则将相应的信息通知买房者。
代码如下:
import java.util.*;class HouseSellCenter extendsObservable
{publicString name;public floatprice;public HouseSellCenter(String name, floatprice)
{this.name =name;this.price =price;
}public void changePrice(floatprice)
{this.price =price;super.setChanged();super.notifyObservers(price);
}publicString toString()
{return "name:" + this.name + " price:" +this.price;
}
}class Buyer implementsObserver
{publicString name;publicBuyer(String name)
{this.name =name;
}public voidupdate(Observable o, Object arg)
{
HouseSellCenter hsc=(HouseSellCenter)o;
System.out.println(this.name+"观察到:"+hsc.name+"房价变为:" + arg + "万");
}
}classHello
{public static voidmain(String[] args)
{
HouseSellCenter hsc= new HouseSellCenter("金悦城",1.3f);
Buyer buyer1= new Buyer("金旭地产");
Buyer buyer2= new Buyer("龙城中介");
Buyer buyer3= new Buyer("祥龙置业");
hsc.addObserver(buyer1);
hsc.addObserver(buyer2);
hsc.addObserver(buyer3);
System.out.println("============");
hsc.changePrice(1.5f);
System.out.println("============");
sleep(3000);
System.out.println("============");
hsc.changePrice(1.2f);
System.out.println("============");
}public static void sleep(inttimeSpan)
{try{
Thread.sleep(timeSpan);
}catch(Exception e)
{
System.out.println(e);
}
}
}
输出结果：
============祥龙置业观察到:金悦城房价变为:1.5万
龙城中介观察到:金悦城房价变为:1.5万
金旭地产观察到:金悦城房价变为:1.5万============
============祥龙置业观察到:金悦城房价变为:1.2万
龙城中介观察到:金悦城房价变为:1.2万
金旭地产观察到:金悦城房价变为:1.2万============
上面的代码是利用了Java对观察者模式的支持。下面用另一个例子说明观察者模式运行规则。
Observerable接口(定义被观察者的规范):
public interfaceObserverable
{voidaddObserver(ObserverBehavior newObserver);voidremoveObserver(ObserverBehavior observerToBeRemoved);voidnotifyAllObservers();
}
ObserverBehavior接口(定义观察者的规范)：
public interfaceObserverBehavior
{void update(float temperature, float humidity, floatpressure);
}
WeatherData类实现Observerable接口，其是真实的被观察者类:
importjava.util.List;importjava.util.ArrayList;public class WeatherData implementsObserverable
{private ListobserverList;private floattemperature;private floathumidity;private floatpressure;publicWeatherData()
{this.observerList = new ArrayList();
}
@Overridepublic voidaddObserver(ObserverBehavior newObserver)
{//TODO Auto-generated method stub
this.observerList.add(newObserver);
}
@Overridepublic voidnotifyAllObservers()
{//TODO Auto-generated method stub
for(ObserverBehavior observer : this.observerList)
{
observer.update(this.temperature, this.humidity, this.pressure);
}
}
@Overridepublic voidremoveObserver(ObserverBehavior observerToBeRemoved)
{//TODO Auto-generated method stub
this.observerList.remove(observerToBeRemoved);
}public void weatherChanged(float temperature, float humidity, floatpressure)
{this.temperature =temperature;this.humidity =humidity;this.pressure =pressure;this.notifyAllObservers();
}
}
MobileDevices实现ObserverBehavior类(真正的观察者)：
public class MobileDevices implementsObserverBehavior
{privateString name;publicMobileDevices(String name)
{this.name =name;
}
@Overridepublic void update(float temperature, float humidity, floatpressure)
{//TODO Auto-generated method stub
System.out.println(this.name + "观察到当前 --> 温度:" + temperature + " 湿度:" + humidity + " 气压:" +pressure);
}
@Overridepublic booleanequals(Object obj)
{if(this ==obj)return true;if(!(obj instanceofMobileDevices))return false;
MobileDevices otherOne=(MobileDevices)obj;if(this.name.equals(otherOne.name))return true;else
return false;
}
}
WhiteBoard实现了ObserverBehavior类(另一个真正的观察者):
public class WhiteBoard implementsObserverBehavior
{privateString name;publicWhiteBoard(String name)
{this.name =name;
}
@Overridepublic void update(float temperature, float humidity, floatpressure)
{//TODO Auto-generated method stub
System.out.println(this.name + "观察到当前 --> 温度:" + temperature + " 湿度:" + humidity + " 气压:" +pressure);
}
}
主方法测试：
public classTester
{/***@paramargs*/
public static voidmain(String[] args)
{//TODO Auto-generated method stub
WeatherData subject = newWeatherData();
WhiteBoard wb= new WhiteBoard("中央广场白板");
MobileDevices iphone= new MobileDevices("iphone手机");
MobileDevices android= new MobileDevices("安卓手机");
subject.addObserver(wb);
subject.addObserver(iphone);
subject.weatherChanged(12, 23, 33);
subject.removeObserver(new MobileDevices("iphone手机"));
subject.addObserver(android);
subject.weatherChanged(22, 43, 25);
}
}
输出结果：
中央广场白板观察到当前 --> 温度:12.0 湿度:23.0 气压:33.0
iphone手机观察到当前 --> 温度:12.0 湿度:23.0 气压:33.0
中央广场白板观察到当前 --> 温度:22.0 湿度:43.0 气压:25.0
安卓手机观察到当前 --> 温度:22.0 湿度:43.0 气压:25.0
总结:
被观察者应该具备以下功能:
1) 能增加一个观察者 addObserver
2)能移除一个观察者 removeObserver
3)在数据改变的时候能将相应的信息通知给被观察者 notifyAllObservers
观察者应具备以下功能:
1) update方法用于观察者接收被观察者的推送信息