设计模式2-观察者模式

package DesignPattern;

import java.util.ArrayList;

public class ObserverPattern {
    //来自Head First 设计模式
    interface Subject{
        void registerObserver(Observer observer);
        void removeObserver(Observer observer);
        void notifyObservers();
    }
    interface Observer{
        void update(float temperature,float humidity,float pressure);
    }
    interface DisplayElement{
        void display();
    }

    public static class WeathData implements Subject{
        private  ArrayList<Observer> observers;
        private float temperature;
        private float humidity;
        private float pressure;

        public WeathData(){
            observers= new ArrayList<>();
        }

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

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

        @Override
        public void notifyObservers() {
            for(Observer observer:observers){
                observer.update(temperature,humidity,pressure);
            }
        }

        public void measurementChanged(){
            notifyObservers();
        }

        public void setMeasurements(float t,float h,float p){
            this.temperature=t;
            this.humidity=h;
            this.pressure=p;
            measurementChanged();
        }
    }

    public static class CurrentConditionsDisplay implements Observer,DisplayElement{
        private float temperature;
        private float humidity;
        private Subject weatherData;
        CurrentConditionsDisplay(Subject weatherData){
            this.weatherData=weatherData;
            weatherData.registerObserver(this);
        }

        @Override
        public void update(float t,float h,float p) {
            this.temperature=t;
            this.humidity=h;
            display();
        }

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

    public static class StaticsDisplay implements Observer,DisplayElement{
        private float temperature;
        private Subject weatherData;
        StaticsDisplay(Subject weatherData){
            this.weatherData=weatherData;
            weatherData.registerObserver(this);
        }

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

        @Override
        public void display() {
            System.out.println("Statics temperature:"+temperature);
        }
    }

    public static void main(String[] args) {
        WeathData weathData = new WeathData();
        CurrentConditionsDisplay ccd = new CurrentConditionsDisplay(weathData);
        StaticsDisplay sd = new StaticsDisplay(weathData);

        weathData.setMeasurements(80,65,30.4f);
        weathData.setMeasurements(82,70,29.2f);
        weathData.setMeasurements(78,90,29.2f);
    }
}