工厂方法模式

【1】什么是工厂方法模式？

定义一个创建产品对象的工厂接口（IFactory），将实际创建工作推迟到子类(addFactory、subFactory、mulFactory、divFactory)当中。

核心工厂类(IFactory)不再负责产品的创建，仅作为一个抽象（有纯虚方法）工厂角色，只负责声明具体工厂子类必须实现的接口（即纯虚方法）。

这样进一步抽象化的好处：系统在不需要修改具体工厂角色的情况下引进新的产品（与简单工厂模式相比）。

【2】工厂方法模式代码示例

示例代码如下：

#include <string>
#include <iostream>
using namespace std;

class Operation
{
protected:
    double m_numberA;
    double m_numberB;

public:
    double getNumberA()
    {
        return m_numberA;
    }

    void setNumberA(double dValue)
    {
        m_numberA = dValue;
    }

    double getNumberB()
    {
        return m_numberB;
    }

    void setNumberB(double dValue)
    {
        m_numberB = dValue;
    }

    virtual double getResult()
    {
        return 0;
    }
};

class addOperation : public Operation
{
public:
    double getResult()
    {
        return m_numberA + m_numberB;
    }
};

class subOperation : public Operation
{
public:
    double getResult()
    {
        return m_numberA - m_numberB;
    }
};

class mulOperation : public Operation
{
public:
    double getResult()
    {
        return m_numberA * m_numberB;
    }
};

class divOperation : public Operation
{
public:
    double getResult()
    {
        return m_numberA / m_numberB;
    }
};

class IFactory
{
public:
    virtual Operation *createOperation() = 0;
};

class AddFactory : public IFactory
{
public:
    static Operation *createOperation()
    {
        return new addOperation();
    }
};

class SubFactory : public IFactory
{
public:
    static Operation *createOperation()
    {
        return new subOperation();
    }
};

class MulFactory : public IFactory
{
public:
    static Operation *createOperation()
    {
        return new mulOperation();
    }
};

class DivFactory : public IFactory
{
public:
    static Operation *createOperation()
    {
        return new divOperation();
    }
};

void main()
{
    Operation *pOper = MulFactory::createOperation();
    pOper->setNumberA(9);
    pOper->setNumberB(99);
    cout << pOper->getResult() << endl;
    
    delete pOper;
    pOper = NULL;

    system("pause");
}

// run out:
/*
891
请按任意键继续. . .
*/

【3】工厂方法模式示例代码

代码如下：

#include <string>
#include <iostream>
using namespace std;

// 抽象产品类1
class IUser
{
public:
    virtual void getUser() = 0;
    virtual void setUser() = 0;
};

// 具体产品类1（SqlUser）
class SqlUser : public IUser
{
public:
    void getUser()
    {
        cout << "在sql中返回user" << endl;
    }
    void setUser()
    {
        cout << "在sql中设置user" << endl;
    }
};

// 具体产品类1（AccessUser）
class AccessUser : public IUser
{
public:
    void getUser()
    {
        cout << "在Access中返回user" << endl;
    }
    void setUser()
    {
        cout << "在Access中设置user" << endl;
    }
};

// 抽象工厂类
class IFactory
{
public:
    virtual IUser *createUser() = 0;
};

// 具体工厂类（SqlFactory）
class SqlFactory : public IFactory
{
public:
    IUser *createUser() 
    {
        return new SqlUser(); // 创建具体产品1（SqlUser）
    }
};

// 具体工厂类（AccessFactory）
class AccessFactory : public IFactory
{
public:
    IUser *createUser()
    {
        return new AccessUser(); // 创建具体产品1（AccessUser）
    }
};

void main()
{
    IFactory* pFactory = new SqlFactory;
    IUser* pUser = pFactory->createUser();
    pUser->getUser();
    pUser->setUser();

    delete pFactory;
    pFactory = new AccessFactory;
    delete pUser;
    pUser = pFactory->createUser();
    pUser->getUser();
    pUser->setUser();

    delete pUser;
    pUser = NULL;

    system("pause");
}

// run out:
/*
在sql中返回user
在sql中设置user
在Access中返回user
在Access中设置user
请按任意键继续. . .
*/

以上代码主要与《抽象工厂模式》对比，为了更好的理解两者之间的区别。

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