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[行为型模式]观察者模式

java 2025/6/20 2:50:38

手机观察者：PhoneDisplay
平板观察者：TabletDisplay
电脑观察者：ComputerDisplay

每个观察者都实现相同的接口 Observer，但具有不同的显示逻辑。

🧱 示例结构

类名	类型	功能描述
`Subject`	接口	定义注册、移除和通知方法
`WeatherData`	具体主题	维护观察者并发送更新通知
`Observer`	接口	定义观察者的更新行为
`PhoneDisplay`	观察者	手机端展示天气信息
`TabletDisplay`	观察者	平板端展示天气信息
`ComputerDisplay`	观察者	电脑端展示天气信息

🔧 接口定义（不变）

`Observer` 接口

public interface Observer {void update(float temperature, float humidity, float pressure);
}

`Subject` 接口

public interface Subject {void registerObserver(Observer o);void removeObserver(Observer o);void notifyObservers();
}

被观察者举例实现

import java.util.ArrayList;
import java.util.List;public class WeatherData implements Subject {private List<Observer> observers;private float temperature;private float humidity;private float pressure;public WeatherData() {observers = new ArrayList<>();}@Overridepublic void registerObserver(Observer o) {observers.add(o);}@Overridepublic void removeObserver(Observer o) {observers.remove(o);}@Overridepublic void notifyObservers() {for (Observer observer : observers) {observer.update(temperature, humidity, pressure);}}public void setMeasurements(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;this.pressure = pressure;notifyObservers();}
}

🏗️ 多个观察者实现

1. 手机观察者 `PhoneDisplay`

public class PhoneDisplay implements Observer {private float temperature;private float humidity;private Subject weatherData;public PhoneDisplay(Subject weatherData) {this.weatherData = weatherData;weatherData.registerObserver(this);}@Overridepublic void update(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;display();}public void display() {System.out.println("[手机] 当前天气: 温度=" + temperature + "°C, 湿度=" + humidity + "%");}
}

2. 平板观察者 `TabletDisplay`

public class TabletDisplay implements Observer {private float temperature;private float humidity;private Subject weatherData;public TabletDisplay(Subject weatherData) {this.weatherData = weatherData;weatherData.registerObserver(this);}@Overridepublic void update(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;display();}public void display() {System.out.println("[平板] 实时气象数据 - 温度：" + temperature + "°C，湿度：" + humidity + "%");}
}

3. 电脑观察者 `ComputerDisplay`

public class ComputerDisplay implements Observer {private float temperature;private float humidity;private float pressure;private Subject weatherData;public ComputerDisplay(Subject weatherData) {this.weatherData = weatherData;weatherData.registerObserver(this);}@Overridepublic void update(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;this.pressure = pressure;display();}public void display() {System.out.println("[电脑] 天气详情：温度=" + temperature + "°C，湿度=" + humidity + "%，气压=" + pressure + "hPa");}
}

🧪 测试客户端代码

public class Client {public static void main(String[] args) {WeatherData weatherData = new WeatherData();// 注册三个不同设备的观察者PhoneDisplay phone = new PhoneDisplay(weatherData);TabletDisplay tablet = new TabletDisplay(weatherData);ComputerDisplay computer = new ComputerDisplay(weatherData);// 模拟数据变化System.out.println("第一次更新数据：");weatherData.setMeasurements(25, 65, 1013);System.out.println("\n第二次更新数据：");weatherData.setMeasurements(27, 70, 1012);}
}

✅ 输出结果示例

第一次更新数据：
[手机] 当前天气: 温度=25.0°C, 湿度=65.0%
[平板] 实时气象数据 - 温度：25.0°C，湿度：65.0%
[电脑] 天气详情：温度=25.0°C，湿度=65.0%，气压=1013.0hPa第二次更新数据：
[手机] 当前天气: 温度=27.0°C, 湿度=70.0%
[平板] 实时气象数据 - 温度：27.0°C，湿度：70.0%
[电脑] 天气详情：温度=27.0°C，湿度=70.0%，气压=1012.0hPa