某实验室欲建立一个实验室环境监测系统，能够显示实验室的温度、湿度以及洁净度等环境数据。当获取到最新的环境测量数据时，显示的环境数据能够更新。
现在采用观察者（Observer）模式来开发该系统。观察者模式的类图如图6-1所示。
【Java代码】
import java.util.*;
interface Observer{
public void update(float temp,float humidity,float cleanness);
}
interface Subject{
public void registerObserver(Observer o);//注册对主题感兴趣的观察者
public void removeObserver(Observer o);//删除观察者
public void notifyObservers（ ）;//当主题发生变化时通知观察者
}
class EnvironmentData implements（1）{
private ArrayList observers;
private float temperature,humidity,cleanness;
public EnvironmentData（ ）{observers=new ArrayList（ ）;}
public void registerObserver(Observer o){observers.add(o);}
public void removeObserver(Observer o){/*代码省略*/}
public void notifyObservers（ ）{
for(int i=0;i＜observers.size（ ）;i++){
Observer observer=(Observer)observers.get(i);
（2）;
}
}
public void measurementsChanged（ ）{（3）;}
public void setMeasurements(float temperature,float humidity,float cleanness){
this.temperature=temperature;
this.humidity=humidity;
this.cleanness=cleanness;
（4）;
}
}
class CurrentConditionsDisplay implements（5）{
private float temperature;
private float humidity;
private float cleanness;
private Subject envData;
public CurrentConditionsDisplay(Subject envData){
this.envData=envData;
（6）;
}
public void update(float temperature,float humidity,float cleanness){
this.temperature=temperature;
this.humidity=humidity;
this.cleanness=cleanness;
display（ ）;
}
public void display（ ）{/*代码省略*/}
}
class EnvironmentMonitor{
public static void main(String[]args){
EnvironmentData envData=new EnvironmentData（ ）;
CurrentConditionsDisplay currentDisplay=new CnrrentConditionsDisplay(envData);
envData.setMeasurements(80,65,30.4f);
}
}
正确答案及解析
正确答案
解析
（1）Subject
（2）observer.update(temperature,humidity,cleanness)
（3）notifyObservers()
（4）measurementsChanged()
（5）Observer
（6）envData.registerObserver(this)
EnvironmentData是环境数据，也就是我们要监测的对象，即主题（Subject），因此（1）处为Subject。
（2）处为通知观察者，因此遍历观察者容器，遍历到一个观察者对象，则更新该观察者的数据，即调用观察者的update()方法。
当环境数据变化时，需要通知观察者，因此（4）处是调用环境变化方法measurementsChanged()，通过此方法通知观察者更新数据，因此（3）处为notifyObservers()。
根据CurrentConditionsDisplay类中的update()方法可知：CurrentConditionsDisplay是个观察者，因此（5）处为Observer
（6）是将观察者添加到主题中去。
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