观察者模式

OO原则：

• 封装变化
• 多用组合、少用继承
• 针对接口编程、不针对实现编程

观察者模式定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有依赖者都会收到通知并自动更新。

不要依赖于观察者被通知的次序。

import java.util.ArrayList;

/**
 * Created by senki on 2015/3/22.
 */
public class WeatherStation {
    public static void main(String[] args) {
       WeatherData weatherData=new WeatherStation().new WeatherData();
       CurrentConditionsDisplay currentDisplay=new WeatherStation().new CurrentConditionsDisplay(weatherData);
        weatherData.setMeasurements(80,65,30.4f);
        weatherData.setMeasurements(82,70,29.2f);
        weatherData.setMeasurements(78,90,29.2f);
}

    public class WeatherData implements Subject{
        private ArrayList observers;
        private float temperature;
        private float humidity;
        private float pressure;

        public WeatherData(){
            observers=new ArrayList();
        }

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

        @Override
        public void removeObserver(Observer o) {
            int i=observers.indexOf(o);
            if(i>=0)
                observers.remove(i);
        }

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

        public void measurementsChanged(){
            notifyObservers();
        }

        public void setMeasurements(float temperature,float humidity,float pressure){
            this.temperature=temperature;
            this.humidity=humidity;
            this.pressure=pressure;
            measurementsChanged();
        }


    }

    public class CurrentConditionsDisplay implements Observer,DisplayElement{
        private float temperature;
        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:"+temperature+"F degress and"+humidity+"% humidity");
        }

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

    public interface Subject{
        public void registerObserver(Observer o);
        public void removeObserver(Observer o);
        public void notifyObservers();
    }
    public interface Observer{
        public void update(float temp,float humidity,float pressure);
    }
    public interface DisplayElement{
        public void display();
    }
}

import java.util.Observable;
import java.util.Observer;

/**
 * Created by senki on 2015/3/22.
 */
public class WeatherStation2 {
    public class WeatherData extends Observable {
        private float temperature;
        private float humidity;
        private float pressure;

        public WeatherData() {
        }

        public void measurementsChanged() {
            setChanged();
            notifyObservers();
        }

        public void setMeasurements(float teperature, float humidity, float presure) {
            this.temperature = teperature;
            this.humidity = humidity;
            this.pressure = presure;
            measurementsChanged();
        }

        public float getTemperature() {
            return temperature;
        }

        public float getHumidity() {
            return humidity;
        }

        public float getPressure() {
            return pressure;
        }
    }

    public class CurrentConditionsDisplay implements Observer, WeatherStation.DisplayElement{
        Observable observable;
        private float temperature;
        private float humidity;

        public CurrentConditionsDisplay(Observable observable){
            this.observable=observable;
            observable.addObserver(this);
        }

        @Override
        public void display() {
            System.out.println("Current conditions:"+temperature+"F degress and"+humidity+"% humidity");
        }

        @Override
        public void update(Observable o, Object arg) {
            if(o instanceof WeatherData){
                WeatherData weatherData=(WeatherData)o;
                this.temperature=weatherData.getTemperature();
                this.humidity=weatherData.getHumidity();
                display();
            }
        }
    }

    public static void main(String[] args) {
        WeatherData weatherData=new WeatherStation2().new WeatherData();
        CurrentConditionsDisplay currentDisplay=new WeatherStation2().new CurrentConditionsDisplay(weatherData);
        weatherData.setMeasurements(80,65,30.4f);
        weatherData.setMeasurements(82,70,29.2f);
        weatherData.setMeasurements(78,90,29.2f);
    }

}