观察者模式 Observer Pattern

,

对象之间常有依赖关系，观察者模式可以让我们方便地监听一个对象，当它发生改变时，其他对象会自动收到通知并作出相应的反应。

实例

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public class Subject {
    private int mState;

    private List<Observer> mObservers = new ArrayList<>();

    public void setState(int state) {
        mState = state;
        notifyObservers();
    }

    @Override
    public String toString() {
        return "State: " + mState;
    }

    public boolean addObserver(Observer o) {
        return mObservers.add(o);
    }

    public boolean removeObserver(Observer o) {
        return mObservers.remove(o);
    }

    private void notifyObservers() {
        for (Observer o : mObservers) {
            o.update(this);
        }
    }

    public interface Observer {
        void update(Subject subject);
    }
}

测试

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Subject subject = new Subject();
subject.setState(0);

Subject.Observer so = System.out::println;
subject.addObserver(so);
subject.setState(1);

subject.removeObserver(so);
subject.setState(2);
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State: 1

实现源码

https://github.com/qianbinbin/DesignPattern/tree/master/src/main/java/io/binac/designpattern/observer

参考资料

  1. Observer pattern - Wikipedia