观察者模式案例用Java内置对象实现

具体思路参考上一篇博客

import java.util.Observable;
 //继承observable，查看源码可以发现，observable已经把注册，添加，删除都做好了，
 //我们不在需要做
 public class WeatherData extends Observable{
     private float temperature;
     private float humidity;
     private float pressure;
     public WeatherData(){
         
     }
     //主题值改变时调用
     public void measurementsChanged(){
         setChanged();//设置当前改变量为true ,这样才可以进行
         notifyObservers();
         //源码：((Observer)arrLocal[i]).update(this, arg);表示向观察者穿值
     }
     //和原来的一样，改变主题的值，引起观察者收到信息
     public void setMeasurements(float temperature,float humidity,float pressure){
         this.temperature=temperature;
         this.humidity=humidity;
         this.pressure=pressure;
         measurementsChanged();
     }
     public float getTemperature() {
         return temperature;
     }
     public float getHumidity() {
         return humidity;
     }
     public float getPressure() {
         return pressure;
     }
     
 }

 public class CurrentConditionsDisplay implements Observer,DisplayElement{
     Observable observable;
     private float temperature;
     private float humidity;
     //传入主题引用，为了把当前观察者放入主题的list中
     public CurrentConditionsDisplay(Observable observable){
         this.observable=observable;
         observable.addObserver(this);
     }
     //更新后执行，显示，供用户观看
     @Override
     public void display() {
         // TODO Auto-generated method stub
         System.out.println("Current conditions: "+temperature
                 +"F degrees and "+humidity+"% humidity");
     }
     //这个函数供主题调用
     @Override
     public void update(Observable o, Object arg) {
         // TODO Auto-generated method stub
         if(o instanceof WeatherData){
             WeatherData weatherData=(WeatherData)o;
             this.temperature=weatherData.getTemperature();
             this.humidity=weatherData.getHumidity();
             display();
         }
     }
 }

测试：

public static void main(String[] args) {
         // TODO Auto-generated method stub
         WeatherData weatherData=new WeatherData();
         CurrentConditionsDisplay currentDisplay=
                 new CurrentConditionsDisplay(weatherData);
         CurrentConditionsDisplay currentDisplay1=
                 new CurrentConditionsDisplay(weatherData);
         weatherData.setMeasurements(80, 65,30.5f);
         weatherData.setMeasurements(82, 70,29.2f);
         weatherData.setMeasurements(78, 90,29.2f);