Java大数据平台开发 学习笔记（48）—— java设计模式（观察者模式）知识汇总

一、前言：

1. 观察者模式还有一个名字叫发布-订阅模式，我们熟悉的消息队列如ActiveMQ，就是采用的这种设计模式，
2. 总的来说观察者模式主要难理解的地方有两个，一个是发布者对一个或多个观察者的管理，另一个就是实现消息发布者和订阅者之间的解耦。

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二、观察者模式：

2.1、UML 图：

2.2、代码实例：

Step 1) 创建 Obser 接口：

public interface Obser {
    
    
    public void updata(float temperature, float pressure, float humidity);
}

Step 2) 创建 CurrentConditions 实现类：

public class CurrentConditions implements Obser {
    
    
    private float temperature;
    private float pressure;
    private float humidity;

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

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

Step 3) 创建 BaiduSite 抽象类：

public class BaiduSite implements Obser{
    
    
    private float temperature;
    private float pressure;
    private float humidity;

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

    public void display(){
    
    
        System.out.println("*** 百度网站 Temperature：" + temperature + "***");
        System.out.println("*** 百度网站 Pressure：" + pressure + "***");
        System.out.println("*** 百度网站 Humidity：" + humidity + "***");
    }
}

Step 4) 创建 SinaSite 实现类：

public class SinaSite implements Obser{
    
    
    private float temperature;
    private float pressure;
    private float humidity;

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

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

Step 5) 创建 Subject 接口：

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

Step 6) 创建 WeatherData 实现类：

public class WeatherData implements Subject {
    
    
    private float temperature;
    private float pressure;

    private float humidity;
    private ArrayList<Obser> obsers;

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

    public float getTemperature() {
    
    
        return temperature;
    }

    public float getPressure() {
    
    
        return pressure;
    }

    public float getHumidity() {
    
    
        return humidity;
    }

    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(Obser o) {
    
    
        obsers.add(o);
    }

    @Override
    public void removeObserver(Obser o) {
    
    
        if(obsers.contains(o)){
    
    
            obsers.remove(o);
        }
    }

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

Step 7) 创建 main 方法：

public class Client {
    
    
    public static void main(String[] args) {
    
    
        WeatherData weatherData = new WeatherData();

        CurrentConditions currentConditions = new CurrentConditions();
        BaiduSite baiduSite = new BaiduSite();
        SinaSite sinaSite = new SinaSite();

        weatherData.registerObserver(currentConditions);
        weatherData.registerObserver(baiduSite);
        weatherData.registerObserver(sinaSite);

        System.out.println("通知各个注册的观察着，查看信息");
        weatherData.setData(10f, 100f, 30.3f);

    }
}

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• 由 ChiKong_Tam 写于 2020 年 10 月 21 日