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设计模式：观察者模式示例

news 2025/7/21 1:13:36

让我们通过一个天气监测应用的例子来展示观察者模式。在这个应用中，WeatherStation 作为可观察的主题，它会跟踪天气数据的变化。Display 作为观察者，当天气数据更新时会显示最新的信息。

示例代码：

import java.util.ArrayList;
import java.util.List;

// 观察者接口
interface Observer {
    void update(float temperature, float humidity, float pressure);
}

// 可观察对象接口
interface Observable {
    void registerObserver(Observer o);
    void removeObserver(Observer o);
    void notifyObservers();
}

// 具体可观察对象：WeatherStation
class WeatherStation implements Observable {
    private List<Observer> observers;
    private float temperature;
    private float humidity;
    private float pressure;

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

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

    public void measurementsChanged() {
        notifyObservers();
    }

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

    @Override
    public void removeObserver(Observer o) {
        observers.remove(o);
    }

    @Override
    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update(temperature, humidity, pressure);
        }
    }
}

// 具体观察者：Display
class Display implements Observer {
    private Observable weatherStation;

    public Display(Observable weatherStation) {
        this.weatherStation = weatherStation;
        weatherStation.registerObserver(this);
    }

    @Override
    public void update(float temperature, float humidity, float pressure) {
        System.out.println("Current conditions: " + temperature + "C degrees and " + humidity + "% humidity");
    }

    public void unsubscribe() {
        weatherStation.removeObserver(this);
    }
}

// 客户端代码
public class ObserverPatternExample {
    public static void main(String[] args) {
        WeatherStation weatherStation = new WeatherStation();
        Display currentDisplay = new Display(weatherStation);

        // 模拟新的天气测量数据
        weatherStation.setMeasurements(28.2f, 65f, 1013.1f);
        weatherStation.setMeasurements(22.1f, 70f, 1012.5f);

        // 当不再需要显示当前天气情况时，取消订阅
        currentDisplay.unsubscribe();

        // 即使更新了天气数据，Display 也不会收到通知
        weatherStation.setMeasurements(25.5f, 60f, 1014.9f);
    }
}