Java:应用Observer接口实践Observer模式(转)
转自:http://zhangjunhd.blog.51cto.com/113473/68949? ?
在Java中通过Observable类和Observer接口实现了观察者模式。Observer对象是观察者，Observable对象是被观察者。
1.?实现观察者模式实现观察者模式非常简单，[1]创建被观察者类，它继承自java.util.Observable类；[2]创建观察者类，它实现java.util.Observer接口；[3]对于被观察者类，添加它的观察者：void addObserver(Observer?o)addObserver()方法把观察者对象添加到观察者对象列表中。?当被观察事件发生时，执行：setChanged();notifyObservers();setChange()方法用来设置一个内部标志位注明数据发生了变化；notifyObservers()方法会去调用观察者对象列表中所有的Observer的update()方法，通知它们数据发生了变化。只有在setChange()被调用后，notifyObservers()才会去调用update()。?[4]对于观察者类，实现Observer接口的唯一方法updatevoid update(Observable?o, Object?arg)形参Object?arg，对应一个由notifyObservers(Object?arg);传递来的参数，当执行的是notifyObservers();时，arg为null。2.实例一NumObserable是一个被观察者，当它的成员变量data的数值发生变化时，会通知所有的观察者。NumObserable.javapackage?com.zj.observer;import?java.util.Observable;?public?class?NumObservable?extends?Observable {????private?int?data?= 0;?????public?int?getData() {???????return?data;????}?????public?void?setData(int?i) {???????data?= i;???????setChanged();???????notifyObservers();????}}?NumObserver是观察者。当它的被观察者(NumObserable)执行了notifyObservers()后，它会执行uodate()方法。NumObserver.javapackage?com.zj.observer;import?java.util.Observable;import?java.util.Observer;?public?class?NumObserver?implements?Observer{????public?void?update(Observable o, Object arg) {???????NumObservable myObserable=(NumObservable) o;???????System.out.println("Data has changed to "+myObserable.getData());????}}?测试类SingleTest，在这里将观察者加入到被观察者的观察列表中。SingleTest.javapackage?com.zj.observer;?public?class?SingleTest {????public?static?void?main(String[] args) {???????NumObservable number =?new?NumObservable();???????number.addObserver(new?NumObserver());???????number.setData(1);???????number.setData(2);???????number.setData(3);????}}结果：Data has changed to 1Data has changed to 2Data has changed to 33.实例二这个实例中，还是对data进行观察，拥有两个观察者，分别观察奇数和偶数的变化，通过notifyObservers(arg)中的参数arg来识别通知信息。被观察者NumsObservable.javapackage?com.zj.observers;import?java.util.Observable;?public?class?NumsObservable?extends?Observable {????public?final?static?Integer?ODD?= 1;????public?final?static?Integer?EVEN?= 2;????private?int?data?= 0;?????public?int?getData() {???????return?data;????}?????public?void?setData(int?i) {???????data?= i;???????Integer flag =?EVEN;???????if?((data?& 0x0001) == 1)???????????flag =?ODD;???????setChanged();???????notifyObservers(flag);????}}?奇数观察者OddObserver.javapackage?com.zj.observers;import?java.util.Observable;import?java.util.Observer;?public?class?OddObserver?implements?Observer {????public?void?update(Observable o, Object arg) {???????if?(arg == NumsObservable.ODD) {???????????NumsObservable myObserable = (NumsObservable) o;???????????System.out.println("OddObserver:Data has changed to "?+ myObserable.getData());???????}????}}?偶数观察者EvenObserver.javapackage?com.zj.observers;import?java.util.Observable;import?java.util.Observer;?public?class?EvenObserver?implements?Observer {????public?void?update(Observable o, Object arg) {???????if?(arg == NumsObservable.EVEN) {???????????NumsObservable myObserable = (NumsObservable) o;???????????System.out.println("EvenObserver:Data has changed to "?+ myObserable.getData());???????}????}}?测试类MultiTest.javapackage?com.zj.observers;?public?class?MultiTest {????public?static?void?main(String[] args) {???????NumsObservable number =?new?NumsObservable();???????number.addObserver(new?OddObserver());???????number.addObserver(new?EvenObserver());???????number.setData(1);???????number.setData(2);???????number.setData(3);????}}结果：OddObserver:Data has changed to 1EvenObserver:Data has changed to 2OddObserver:Data has changed to 3