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5-1所示。
【C++代码】
#include＜iostream>
#include＜vector>
using namespace std;
class Observer{
public:
virtual void update(float temp,float humidity,float cleanness)=0;
};
class Subject{
public:
virtual void registerObserver(Observer*o)=0;//注册对主题感兴趣的观察者
virtual void removeObserver(Observer*o)=0;//删除观察者
virtual void notifyObservers（ ）=0;//当主题发生变化时通知观察者
};
class EnvironmentData:public（1）{
private:
vector＜Observer*>observers;
float temperature,humidity,cleanness;
public:
void registerObserver(Observer*o){observers.push_back(o);}
void removeObserver(Observer*o){/*代码省略*/}
void notifyObservers（ ）{
for(vector＜Observer*>::const_iterator it=observers.begin（ ）;it!=observers.end（ ）;it++)
{（2）;}
}
Void measurementsChanged（ ）{（3）;}
void setMeasurements(float temperature,float humidity,float cleanness){
this->temperature=temperature;
this->humidity=humidity;
this->cleanness=cleanness;
（4）;
}
};
class CurrentConditionsDisplay:public（5）{
private:
float temperature,humidity,cleanness;
Subject*envData;
public:
CurrentConditionsDisplay(Subject*envData){
this->envData=envData;
（6）;
}
void update(float temperature,float humidity,float cleanness){this->temperature=temperature;
this->humidity=humidity;
this->cleanness=cleanness;
display（ ）;
}
void display（ ）{/*代码省略*/}
};
int main（ ）{
EnvironmentData*envData=new EnvironmentData（ ）;
CurrentConditionsDisplay*currentDisplay=new CurrentConditionsDisplay(envData);
envData->setMeasurements(80,65,30.4f);
return 0;
}
正确答案及解析
正确答案
解析
（1）Subject
（2）(*it)->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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