java设计模式（一）---观察者模式

观察者模式
定义：出版者+订阅者=观察者模式
出版者称为“主题”，订阅者称为“观察者”。
上代码：

    //=========主题接口============
    public interface Subject{
        //注册观察者
        public void registerObserver(Observer o);
        //移除观察者
        public void removeObserver(Observer o);
        //主题改变，通知观察者
        public void notifyObservers(); 
    }
    //=========观察者接口==========
    public interface Observer{
        //当气象值改变时，主题会把这些状态值当作方法的参数，传送给观察者
        public void update(float temp,float humidity,float pressure);
    }
    //=========当布告板需要显示时调用此方法========
    public interface DisplayElement{
        public void display();
    }

//weatherData 实现主体接口
    public class WeatherData implements Subject{
       private ArrayList observers;
       private float temperature;
       private float humidity;
       private float pressure;

       public weatherData(){
         observers = new ArrayList();
       }
       //注册为观察者
       public void registerObserver(Observer o){
         observers.add(o);
       }
       //移除观察者
       public void removeObserver(Observer o){
        int i = observers.indexof(o);
        if(i >= 0){
          observers.remouve(i);
        }
        observers.remouve(o);
       }
       //通知观察者
       public void notifyObservers(){
        for(int i = 0;i<observers.size();i++){
          Observer observe = observers.get(i);
          observe.update(temperature.humidity,pressure);
        }
       }
       //各个状态改变调用通知观察者方法
       public void measurementsChanged(){
       notifyObservers();
       }

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

//建立布告板
    public class CurrentConditionsDisplay implements Observer,DisplayElement{
        private float temperature;
        private float humidity;
        private Subject weatherData;
        //构造方法
        public CurrentConditionsDisplay(){
         this.weatherData = weatherData;
         weatherData.registerObserver(this);
        }
        //更新各个状态
        public void update(float temperature,float humidity,private pressure){
         this.temperature =temperature;
         this.humidity  = humidity;
         this.pressure = pressure;
         display();
        }
        //显示
        public void display(){
         System.out.println("");
        }
    }

//启动气象站
    public class weatherStation{
         WeatherData weatherData = new WeatherData();
         CurrentConditionsDisplay a = new CurrentConditionsDisplay();//布告板1
         CurrentConditionsDisplay b = new CurrentConditionsDisplay();//布告板2
         CurrentConditionsDisplay c = new CurrentConditionsDisplay();//布告板3
         weatherData.setMeasurements(80,65);
    }