1，定义事件源接口
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package com.pattern.observer;
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObserver();
}
2，定义事件源
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package com.pattern.observer;
import java.util.ArrayList;
/**
* 事件源
*/
public class WeatherData implements Subject {
private ArrayList observers;
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {
observers = new ArrayList();
}
/**
* @see com.pattern.observer.Subject#registerObserver(com.pattern.observer.Observer)
*/
@Override
public void registerObserver(Observer o) {
observers.add(o);
}
/**
* @see com.pattern.observer.Subject#removeObserver(com.pattern.observer.Observer)
*/
@Override
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if (i >= 0) {
observers.remove(i);
}
}
/**
* @see com.pattern.observer.Subject#notifyObserver()
*/
@Override
public void notifyObserver() {
for(int i=0;i
Observer observer = (Observer)observers.get(i);
observer.update(temperature, humidity, pressure);
}
}
public void measurementsChanged(){
notifyObserver();
}
public void setMeasurements(float temperature,float humidity,float pressure){
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
}
3，定义观察者接口
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package com.pattern.observer;
public interface Observer {
public void update(float temp,float humidity,float pressure);
}
4，定义显示接口
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package com.pattern.observer;
public interface DisplayElement {
public void display();
}
5，观察者实现类
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package com.pattern.observer;
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);
}
/**
* @see com.pattern.observer.DisplayElement#display()
*/
@Override
public void display() {
System.out.println("Current conditions: "+temperature +"F degrees and "+humidity+"% humidity");
}
/**
* @see com.pattern.observer.Observer#update(float, float, float)
*/
@Override
public void update(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
display();
}
}
6,测试
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package com.pattern.observer;
public class WeatherStation {
public static void main