Java 设计模式（行为型）

观察者设计模式（Observer）

Posted by 余腾 on 2019-08-19
Estimated Reading Time 3 Minutes
Words 575 In Total
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什么是观察者设计模式？

观察者设计模式 —> 行为型模式

观察者模式：对象之间多对一依赖的一种设计方案，被依赖的对象为 Subject，依赖的对象为 Observer。

Subject 通知 Observer 变化。

  • Observer：接收输入

  • Subject：登记注册、移除和通知

    • registerObserver：注册
    • removeObserver：移除
    • notifyObservers()：通知所有注册用户，可以更新数据，让主动获取，也可以 Subject 时时推送。

Subject

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

Observer

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

WeatherData

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import java.util.ArrayList;

public class WeatherData implements Subject {
    private float temperature;
    private float pressure;
    private float humidity;
    private ArrayList<Observer> observers;//观察者集合


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

    public float getTemperature() {
        return temperature;
    }

    public float getPressure() {
        return pressure;
    }

    public float getHumidity() {
        return humidity;
    }

    //主动推送
    public void dataChange() {
        notifyObservers();
    }

    public void setData(float temperature, float pressure, float humidity) {
        this.temperature = temperature;
        this.pressure = pressure;
        this.humidity = humidity;
        dataChange();
    }

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

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

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

CurrentConditions

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public class CurrentConditions implements Observer {

    private float temperature;
    private float pressure;
    private float humidity;

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

    public void display() {
        System.out.println("=========CurrentConditions===========");
        System.out.println("Today Temperature: " + temperature);
        System.out.println("Today Pressure: " + pressure);
        System.out.println("Today Humidity: " + humidity);
    }
}

OtherConditions

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public class OtherConditions implements Observer {

    private float temperature;
    private float pressure;
    private float humidity;

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

    public void display() {
        System.out.println("=========OtherConditions===========");
        System.out.println("Other Today Temperature: " + temperature);
        System.out.println("Other Today Pressure: " + pressure);
        System.out.println("Other Today Humidity: " + humidity);
    }
}

Client

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public class Client {

	public static void main(String[] args) {

		//创建 Subject WeatherData 数据源
		WeatherData weatherData = new WeatherData();
		//创建观察者 Observer
		CurrentConditions conditions = new CurrentConditions();
		//把观察者注册进 Subject
		weatherData.registerObserver(conditions);

		//再注册进一个
		weatherData.registerObserver(new OtherConditions());

		System.out.println("========更新数据，并通知观察者========");
		weatherData.setData(20L,160L,50L);

		System.out.println();
		System.out.println("=======Remove CurrentConditions=======");
		weatherData.removeObserver(conditions);
		weatherData.notifyObservers();
	}
}

//TODO
========更新数据，并通知观察者========
=========CurrentConditions===========
Today Temperature: 20.0
Today Pressure: 160.0
Today Humidity: 50.0
=========OtherConditions===========
Other Today Temperature: 20.0
Other Today Pressure: 160.0
Other Today Humidity: 50.0

=======Remove CurrentConditions=======
=========OtherConditions===========
Other Today Temperature: 20.0
Other Today Pressure: 160.0
Other Today Humidity: 50.0

观察者模式 JDK 应用源码分析

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