观察者模式就是一个对象在被调用或者初始化的时候,去触发其他对象的方法
每当发布天气预报时,会通知当地的居民,居民就是观察者(Observer),天气预报就是被观察者(Subject)
/*** \观察者接口*/
interface Observer {void update(WeatherData weatherData);
}
/*** 具体的居民类(观察者类)*/
class ConcreteResident implements Observer {private String name;public ConcreteResident(String name) {this.name = name;}public void update(WeatherData weatherData) {System.out.println(name + " 收到天气预报,温度:" + weatherData.getTemperature() + "℃,湿度:" + weatherData.getHumidity() + "%。");}
}
当被观察者发生变化时,会通知已添加在主体列表中的观察者
/*** // 天气预报中心接口(主题接口)*/
public interface WeatherCenter {void addObserver(Observer observer);void removeObserver(Observer observer);void notifyObservers(WeatherData weatherData);
}
import java.util.ArrayList;
import java.util.List;/*** 具体的天气预报中心类*/class ConcreteWeatherCenter implements WeatherCenter {private List<Observer> observers = new ArrayList<>();public void addObserver(Observer observer) {observers.add(observer);}public void removeObserver(Observer observer) {observers.remove(observer);}public void notifyObservers(WeatherData weatherData) {for (Observer observer : observers) {observer.update(weatherData);}}
}
测试实例
public class ObserverPatternDemo {public static void main(String[] args) {// 创建天气预报中心WeatherCenter weatherCenter = new ConcreteWeatherCenter();// 创建居民(观察者)Observer resident1 = new ConcreteResident("居民A");Observer resident2 = new ConcreteResident("居民B");// 注册观察者weatherCenter.addObserver(resident1);weatherCenter.addObserver(resident2);// 发布新的天气数据WeatherData weatherData = new WeatherData(25.0f, 60.0f);weatherCenter.notifyObservers(weatherData);// 输出:// 居民A 收到天气预报,温度:25.0℃,湿度:60.0%。// 居民B 收到天气预报,温度:25.0℃,湿度:60.0%。// 如果需要移除某个观察者,可以调用 removeObserver 方法// weatherCenter.removeObserver(resident1);}
}