大话设计模式C++实现-第8章-工厂方法模式

一、UML图

二、概念

工厂方法模式（Factory Method）：定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法是一个类的实例化延迟到其子类。

三、包含的角色

（1）抽象工厂

（2）具体工厂

（3）抽象产品

（4）具体产品

四、优势

（1）工厂方法模式是对简单工厂模式的稍微的改进。工厂方法模式的用意是定义一个创建产品对象的工厂接口，将实际工作推迟到子类中。

（2）与简单工厂模式相比，制造产品的工厂类不再 只有一个，而是每种具体产品类都对应一个生产它的具体工厂类。而这些具体工厂类的共同特征再被提取出来形成一个抽象产品类，这些具体产品类都继承自这个抽象产品类。

（3）当需要增加一种产品的时候，需要做的是：增加一种继承自抽象产品的具体产品类，增加一种继承在抽象工厂的具体工厂类，更改客户端。而不需要在简单工厂模式中那样更改工厂内的switch。

五、C++实现

（1）计算器的例子

#include <iostream>#include <cstdlib>using namespace std;//抽象产品类class Operation{protected:double numberA;double numberB;public:double getA(){return numberA;}double getB(){return numberB;}void setA(double number){numberA=number;}void setB(double number){numberB=number;}virtual double GetResult(){double result=0;return result;}};//下面是四个具体产品类class OperationAdd:public Operation{public:double GetResult(){double result=0;result=numberA+numberB;return result;}};class OperationSub:public Operation{public:double GetResult(){double result=0;result=numberA-numberB;return result;}};class OperationMul:public Operation{public:double GetResult(){double result=0;result=numberA*numberB;return result;}};class OperationDiv:public Operation{public:double GetResult(){double result=0;if(numberB!=0)result=numberA/numberB;return result;}};//抽象工厂类class AbstractFactory{public:virtual Operation* createOperation(){return new Operation;}};//下面是四个具体工厂类，分别用于产生四个具体产品class AddFactory:public AbstractFactory{public:Operation* createOperation(){Operation* oper=new OperationAdd;return oper;}};class SubFactory:public AbstractFactory{public:Operation* createOperation(){Operation* oper=new OperationSub;return oper;}};class MulFactory:public AbstractFactory{public:Operation* createOperation(){Operation* oper=new OperationMul;return oper;}};class DivFactory:public AbstractFactory{public:Operation* createOperation(){Operation* oper=new OperationDiv;return oper;}};//客户端void main(){AbstractFactory* af=NULL;af=new AddFactory();Operation* oper=NULL;oper=af->createOperation();oper->setA(1);oper->setB(2);cout<<oper->GetResult()<<endl;if(af!=NULL){delete af;af=NULL;}if(oper!=NULL){delete oper;oper=NULL;}system("pause");}

（2）雷锋工厂的例子

#include <iostream>#include <cstdlib>using namespace std;//抽象产品类：雷锋class Leifeng{public:virtual void Sweep(){cout<<"扫地"<<endl;}virtual void Wash(){cout<<"洗衣"<<endl;}virtual void BuyRice(){cout<<"买米"<<endl;}};//下面是两个具体产品类class Undergraduate:public Leifeng{public:void Sweep(){cout<<"学生-扫地"<<endl;}void Wash(){cout<<"学生-洗衣"<<endl;}void BuyRice(){cout<<"学生-买米"<<endl;}};class Volunteer:public Leifeng{public:void Sweep(){cout<<"志愿者-扫地"<<endl;}void Wash(){cout<<"志愿者-洗衣"<<endl;}void BuyRice(){cout<<"志愿者-买米"<<endl;}};//抽象工厂类class AbstractFactory{public:virtual Leifeng* CreateLeifeng(){return new Leifeng;}};//下面是两个具体工厂类，分别于两个具体产品相对应class UndergraduateFactory:public AbstractFactory{public:Undergraduate* CreateLeifeng(){return new Undergraduate;}};class VolunteerFactory:public AbstractFactory{public:Volunteer* CreateLeifeng(){return new Volunteer();}};//客户端void main(){//想要生产Volunteer产品的话，只需要将此处的UndergraduateFactory更改为VolunteerFactory即可。AbstractFactory* af=NULL;af=new VolunteerFactory;Leifeng* lf=NULL;lf=af->CreateLeifeng();lf->BuyRice();lf->Sweep();lf->Wash();if(af!=NULL){delete af;af=NULL;}if(lf!=NULL){delete lf;lf=NULL;}system("pause");}

（3）运行截图