设计模式-观察者模式

参考Head First 设计模式

观察者模式：定义对象之间一对多的依赖，当“一”发生改变时，所有的依赖者都会收到通知并自动改变，主题与订阅者关系。

定义主题接口Subject

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public interface Subject { public void registerObserver(Observer o); public void removeObserver(Observer o); public void notifyObservers(); }

定义观察者接口Observer

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public interface Observer { public void update(float temp,float humidity,float pressure); }

定义展示面板接口

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public interface DisplayElement { public void display(); }

定义主题实现subject接口

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public class WeatherData implements Subject { private ArrayList<Observer> 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 = observers.get(i); observer.update(temperature,humidity,pressure); } } public void messurementChanged(){ notifyObservers(); } public void setMessurements(float temperature,float humidity,float pressure){ this.temperature = temperature; this.humidity = humidity; this.pressure = pressure; messurementChanged(); } }

定义观察者实现，观察者接口，展示接口

/** * @description: * @author: zhangyh * @create :2018/6/2 */ 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 update(float temperature, float humidity, float pressure) { this.temperature = temperature; this.humidity = humidity; display(); } @Override public void display() { System.out.println( "CurrentConditionsDisplay{" + "temperature=" + temperature + ", humidity=" + humidity + '}'); } }

观察者2

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public class ForecastConditionsDisplay implements Observer,DisplayElement { private float temperature; private float humidity; private Subject weatherData; public ForecastConditionsDisplay(Subject weatherData){ this.weatherData = weatherData; weatherData.registerObserver(this); } @Override public void update(float temperature, float humidity, float pressure) { this.temperature = temperature; this.humidity = humidity; display(); } @Override public void display() { System.out.println( "ForecastConditionsDisplay{" + "temperature=" + temperature + ", humidity=" + humidity + '}'); } }

测试

/** * @description: * @author: zhangyh * @create :2018/6/2 */ public class WeatherDataStation { public static void main(String[] args){ WeatherData weatherData = new WeatherData(); CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(weatherData); ForecastConditionsDisplay forecastConditionsDisplay = new ForecastConditionsDisplay(weatherData); weatherData.setMessurements(80,66,30.4F); weatherData.setMessurements(80,67,30.5F); weatherData.setMessurements(80,68,30.6F); } }当主题发生变化时通知各个订阅者。