Java设计模式 -- 观察者模式(push方式)

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。

当两个对象之间松耦合，他们依然可以交互，但是不太清楚彼此的细节。观察者模式提供了一种对象设计让主题和观察者之间松耦合。

 

我们来看看一种push方式的 观察者模式。

 

首先是观察者 主题 等的接口。

//主题public interface Subject {public void registerObserver(Observer o);public void removeObserver(Observer o);public void notifyObservers();}//观察者public interface Observer {public void update(float temp, float humidity, float pressure);}//other 操作public interface DisplayElement {public void display();}

 

实现这些接口。

//实现主题public class WeatherData implements Subject{private ArrayList observers;private float temperature;private float humidity;private float pressure;public WeatherData(){observers = new ArrayList();}public void notifyObservers() {// TODO Auto-generated method stubfor(int i=0, len=observers.size(); i < len; i++){Observer observer = (Observer) observers.get(i);observer.update(temperature, humidity, pressure);}}public void registerObserver(Observer o) {// TODO Auto-generated method stubobservers.add(o);}public void removeObserver(Observer o) {// TODO Auto-generated method stubint i = observers.indexOf(o);if(i >= 0){observers.remove(i);}}public void measurementsChange(){notifyObservers();}public void setMeasurements(float temperature, float humidity, float pressure){this.temperature = temperature;this.humidity = humidity;this.pressure = pressure;measurementsChange();}}//实现观察者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);}public void update(float temp, float humidity, float pressure) {// TODO Auto-generated method stubthis.temperature = temp;this.humidity = humidity;display();}public void display() {// TODO Auto-generated method stubSystem.out.println("Current conditions: "+ temperature + "F degrees and " + humidity + "% humidity");}}

 

实现完了这些接口，测试观察者模式

public class WeatherStation {public static void main(String[] args){WeatherData weatherData = new WeatherData();CurrentConditionsDisplay display = new CurrentConditionsDisplay(weatherData);weatherData.setMeasurements(80, 65, 30.4f);weatherData.setMeasurements(82, 76, 30.2f);weatherData.setMeasurements(78, 90, 29.4f);}}