设计模式—观察者模式

观察者模式

定义

定义对象间一种一对多的依赖关系，使得每当一个对象改变状态，则所有依赖它的对象都会得到通知并被自动更新

代码

被观察者

public abstract class Subject {

    private Vector<MyObserver> observerVector = new Vector<>();

    public void addObserver(MyObserver observer){
        this.observerVector.add(observer);
    }

    public void delObserver(MyObserver observer){
        this.observerVector.remove(observer);
    }

    public void notifyObservers(){
        for (MyObserver observer : this.observerVector) {
            observer.update();
        }
    }
}

被观察者的实现

public class ConcreteSubject extends Subject {

    public void doSomething(){
        System.out.println("subject do something");
        super.notifyObservers();
    }
}

观察者

public interface MyObserver {

    void update();
}

观察者的实现

public class ConcreteMyObserver implements MyObserver {
    @Override
    public void update() {
        System.out.println("observer receive notify info!");
    }
}

测试

public class ConcreteObserverTest {
    @Test
    public void testObserver(){
        ConcreteSubject subject = new ConcreteSubject();
        MyObserver observer = new ConcreteMyObserver();
        subject.addObserver(observer);
        subject.doSomething();
    }
}

扩展

JDK已经自带了Observable类和Observer接口，修改上面的代码

被观察者

public abstract class Subject extends Observable{

}

---

public class ConcreteSubject extends Subject {

    public void doSomething(){
        System.out.println("subject do something");
        super.setChanged();
        super.notifyObservers("from subject");
    }
}

观察者

public interface MyObserver extends Observer {

}

---

public class ConcreteMyObserver implements MyObserver {
    @Override
    public void update(Observable o, Object arg) {
        System.out.println("observer receive:"+arg.toString());
    }
}

测试

public class ConcreteObserverTest {
    @Test
    public void testObserver(){
        ConcreteSubject subject = new ConcreteSubject();
        MyObserver observer = new ConcreteMyObserver();
        subject.addObserver(observer);
        subject.doSomething();

    }
}