设计模式之观察者模式
工作要求:需要建立一个气象观测站,该气象站必须建立申请的WeatherData对象,WeatherData对象负责追踪天气状况(温度,湿度,气压)。需求需要三张布告板,当WeatherData气象站获得最新数据时,必须实时更新三张布告板的信息。
大致画图如下。
分析
情景: 气象站观测温度变化,当改变时需要通过其他布告板的信息。
问题: 怎么温度一变化就通知其他的布告板。
解决方案: 应用观察者模式,布告板作为观察者,气象站作为被观察者,观察者关心的数据发生变化时,被观察者告知所 有观察者。
为了应用的可拓展性,我们必须将布告板与气象站进行分离,当系统维护时,增加新的布告板时,拓展性强,并且并不会影响气象站代码的变更。
代码实现:
被观察者定义接口(必须具有注册观察者功能,删除观察者功能,告知所有观察者功能)
package cn.pattern.observer;
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObservers();
}
观察者接口(通知时改变布告板上的值并进行展示)
package cn.pattern.observer;
public interface Observer {
public void update(float temperature,float humidity,float pressure);
}
定义展示接口
package cn.pattern.observer;
public interface DisplayElement {
public void display();
}
气象站实现(被观察者)
package cn.pattern.observer;
import java.util.ArrayList;
public class WeatherData implements Subject {
//通知的观察者集合
private ArrayList observers;
//温度
private float temperature;
//湿度
private float humidity;
//气压
private float pressure;
public WeatherData() {
observers = new ArrayList();
}
//注册观察者
@Override
public void registerObserver(Observer o) {
observers.add(o);
}
//删除观察者(当布告板不需要实时更新时,可以删除观察者)
@Override
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if(i<0) {
observers.remove(i);
}
}
//通知所有观察者
@Override
public void notifyObservers() {
for (int i = 0; i < observers.size(); i++) {
Observer observer = (Observer)observers.get(i);
observer.update(temperature, humidity, pressure);
}
}
//设置温度(当温度改变时,进行设置,然后通知所有观察者)
public void setMessurements(float temperature,float humidity,float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
notifyObservers();
}
}
观察者实现1
package cn.pattern.observer;
public class CurrentConditionsDisplay implements Observer,DisplayElement {
private float temperature;
private float humidity;
private float pressure;
private Subject weatherData;
public CurrentConditionsDisplay(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
@Override
public void display() {
System.out.println("Display \t"+"Current conditions:" + temperature + "F degrees amd" + humidity +"% humidity" +".local pressure "+ pressure);
}
@Override
public void update(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
display();
}
}
观察者实现2
package cn.pattern.observer;
public class CurrentConditionsDisplay1 implements Observer,DisplayElement {
private float humidity;
private float pressure;
private Subject weatherData;
public CurrentConditionsDisplay1(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
@Override
public void display() {
System.out.println("Display1\t"+"Current conditions:" + " amd" + humidity +"% humidity" +".local pressure "+ pressure);
}
@Override
public void update(float temperature, float humidity, float pressure) {
this.humidity = humidity;
this.pressure = pressure;
display();
}
}
测试程序代码实现
package cn.pattern.observer;
public class WeatherStation {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentDisplsy = new CurrentConditionsDisplay(weatherData);
CurrentConditionsDisplay1 currentDisplsy1 = new CurrentConditionsDisplay1(weatherData);
weatherData.setMessurements(80, 65, 30.4f);
weatherData.setMessurements(82, 70, 29.2f);
weatherData.setMessurements(78, 90, 29.2f);
}
}
console输出如下