首先，实现观察者、被观察者接口

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public interface Subject {
    void registerObserver(Observer o); //注册观察者
    void removeObserver(Observer o); //删除观察者
    void notifyObservers(); //当被观察者状态改变时，通知所有观察者信息
}
public interface Observer {
    //当被观察者的数据更新时，将更新的信息当做参数传递给观察者
    void update(float temperature, float humidity, float pressure);
}
public interface DisplayElement {
    void display(); //用于显示更新的数据
}

被观察者对象的实现

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//被观察对象实现被观察接口
public class WeatherData implements Subject {
    private ArrayList<Observer> observers;
    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() {
        observers = new ArrayList<Observer>();
    }

    @Override
    public void registerObserver(Observer o) {
        observers.add(o);
    }

    @Override
    public void removeObserver(Observer o) {
        int i = observers.indexOf(o);
        if (i >= 0) {
            observers.remove(i);
        }
    }

    public void notifyObservers() {
        for (int i = 0; i < observers.size(); i++) {
            Observer observer = observers.get(i);
            observer.update(temperature, humidity, pressure);
        }
    }

    public void measurementsChanged(){
        notifyObservers();
    }

    public void setMeasurements(float temperature,float humidity,float pressure){
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }
}

观察者被观察者逻辑的具体实现

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//观察者实现观察者接口和具体的数据展示
public class CurrentContionsDisplay implements Observer, DisplayElement {
    private static final String TAG = "CurrentContionsDisplay";
    private float temperature;
    private float humidity;
    private Subject weatherData;

    public CurrentContionsDisplay(Subject weatherData) {
        this.weatherData = weatherData;
        weatherData.registerObserver(this);
    }

    @Override
    public void update(float temperature, float humidity, float pressure) {
        this.temperature = temperature;
        this.humidity = humidity;
        display();
    }

    @Override
    public void display() {
        Log.d(TAG, "display: " + temperature + "::" + humidity);
    }
}

使用实例：

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WeatherData data = new WeatherData();
CurrentContionsDisplay display = new CurrentContionsDisplay(data);
data.setMeasurements(100,100,100);

代码地址

赏

本文地址： http://www.yppcat.top/2019/02/07/观察者模式/