大话设计模式-第八章-工厂方法模式

一、UML图

二、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

三、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。

四、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=new AddFactory;
	Operation* oper=af->createOperation();

	oper->setA(1);
	oper->setB(2);
	cout<<oper->GetResult()<<endl;
	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=new VolunteerFactory;
	Leifeng* lf=af->CreateLeifeng();

	lf->BuyRice();
	lf->Sweep();
	lf->Wash();

	system("pause");
}