观察者模式

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Demo场景：终端通过WeatherData实时显示（获取）变化的数据。

（1）主题接口：Subject

package designpattern.observer.v1;/** * 主题接口 */public interface Subject {    public void registerObserver(Observer o);    public void removeObserver(Observer o);    public void notifyObservers();}

（2）主题接口实现类：WeatherData

package designpattern.observer.v1;import java.util.ArrayList;public class WeatherData implements Subject {    private ArrayList<Observer> observers;    private float temprature;    private float humidity;    private float pressure;    public WeatherData(){        observers = new ArrayList<Observer>();    }    @Override    public void registerObserver(Observer observer) {        observers.add(observer);    }    @Override    public void removeObserver(Observer observer) {        int i = observers.indexOf(observer);        if(i>0){            observers.remove(observer);        }    }    @Override    public void notifyObservers() {        for(int i=0; i<observers.size(); i++){            Observer observer = observers.get(i);            observer.update(temprature, humidity, pressure);        }    }    //检测到变化时，通知观察者    public void measurementsChanged(){        notifyObservers();    }    public void setMeasurements(float temprature, float humidity, float pressure){        this.temprature = temprature;        this.humidity = humidity;        this.pressure = pressure;        measurementsChanged();    }}

（3）观察者接口：Observer

package designpattern.observer.v1;/** * 定义观察者接口 */public interface Observer {    public void update(float temp, float humidity, float pressure);}

（4）观察者play行为接口：DisplayElement

package designpattern.observer.v1;/** *  定义显示这个行为的接口 */public interface DisplayElement {    public void display();}

（5）观察者接口、行为接口实现类：CurrentConditionsDisplay

package designpattern.observer.v1;public class CurrentConditionsDisplay implements Observer, DisplayElement {    private float temprature;    private float humidity;    private Subject weatherData;    public CurrentConditionsDisplay(Subject weatherData){        this.weatherData = weatherData;        weatherData.registerObserver(this);    }    @Override    public void display() {        System.out.println("Current Conditions:" + temprature + "C degrees and " + humidity + "% humidity");    }    @Override    public void update(float temp, float humidity, float pressure) {        this.temprature = temp;        this.humidity = humidity;        display();    }}

演示观察者模式

package designpattern.observer.v1;public class WeatherStation {    public static void main(String[] args) {        //实例化一个主题        WeatherData weatherData = new WeatherData();        CurrentConditionsDisplay currentCondDisplay = new CurrentConditionsDisplay(weatherData);         weatherData.setMeasurements(10, 20, 30.4f);        weatherData.setMeasurements(11, 19, 35.6f);        weatherData.setMeasurements(15, 30, 40.4f);    }}

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