某灯具厂商欲生产一个灯具遥控器，该遥控器具有7个可编程的插槽，每个插槽都有开关按钮，对应着一个不同的灯。利用该遥控器能够统一控制房间中该厂商所有品牌灯具的开关，现采用Command（命令）模式实现该遥控器的软件部分。Command模式的类图如图5-1所示。
【C++代码】
class Light{
public:
Light(string name){/*代码省略*/}
void on（ ）{/*代码省略*/}//开灯
void off（ ）{/*代码省略*/}//关灯
};
class Command{
public:
（1）;
}；
class LightOnCommand:public Command{//开灯命令
private:
Light*light;
public:
LightOnCommand(Light*light){this->light=light;}
void execute（ ）{（2）;}
};
class LightOffCommand:public Command{//关灯命令
private:
Light*light;
public:
LightOffCommand(Light*light){this->light=light;}
void execute（ ）{（3）;}
};
class RemoteControl{//遥控器
private:
Command*onCommands[7];
Command*offCommands[7];
public:
RemoteControl（ ）{/*代码省略*/}
void setCommand(int slot,Command*onCommand,Command*offCommand){
（4）=onCommand;
（5）=offCommand;
}
void onButtonWasPushed(int slot){（6）;}
void offButtonWasPushed(int slot){（7）;}
};
int main（ ）{
RemoteControl*remoteControl=new RemoteControl（ ）;
Light*livingRoomLight=new Light("Living Room");
Light*kitchenLight=new Light("kitchen");
LightOnCommand*livingRoomLightOn=new LightOnCommand(livingRoomLight);
LightOffCommand*livingRoomLightOff=newLightOffCommand(livingRoomLight);
LightOnCommand*kitchenLightOn=new LightOnCommand(kitchenLight);
LightOffCommand*kitchenLightOff=new LightOffCommand(kitchenLight);
remoteControl->setCommand(0,livingRoomLightOn,livingRoomLightOff);
remoteControl->setCommand(1,kitchenLightOn,kitchenLightOff);
remoteControl->onButtonWasPushed(0);
remoteControl->offButtonWasPushed(0);
remoteControl->onButtonWasPushed(1);
remoteControl->offButtonWasPushed(1);
/*其余代码省略*/
return 0;
}
正确答案及解析
正确答案
解析
（1）virtual void execute()=0
（2）light->on()
（3）light->off()
（4）onCommands[slot]
（5）offCommands[slot]
（6）onCommands[slot]->execute()
（7）offCommands[slot]->execute()
本题考查设计模式的实现，难度较小。根据类图和已有代码可写出空缺的代码，书写方式注意java和C++的区别即可。
Command类为所有的命令声明了一个接口，因此需要一个纯虚函数，这个函数根据下面的子类可以看到，应该为execute()，因此第一空填写virtual void execute()=0；
（2）和（3）定义了开灯、关灯action，因此，分别填写（2）light->on()（3）light->off()；
（4）（5）分别设置“开灯”命令对象、“关灯”命令对象，因此分别填写（4）onCommands[slot]（5）offCommands[slot]；
（6）（7）分别完成对开灯、关灯命令对象的execute方法的调用，因此分别填写（6）onCommands[slot]->execute()
（7）offCommands[slot]->execute()。
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