c++ - 工厂方法模式使用继承，而抽象工厂模式使用组合如何？

Question

我正在研究抽象工厂模式与工厂方法模式之间的区别。我了解到工厂方法仅用于创建一个产品，而抽象工厂用于创建相关或依赖产品的系列。但是我不清楚工厂方法模式如何使用继承而抽象工厂模式使用组合。

我知道这个问题被问过几次了，有人可以用下面的代码解释一下继承和组合是如何发生的吗？

工厂方法代码

class IRose
{
public:
virtual string Color(void)=0;
};

class RedRose: public IRose
{
public:
string Color(void)
{
    return "Red";
}
};

class YellowRose: public IRose
{
public:
string Color(void)
{
    return "Yellow";
}
};

class IFactory
{
public:
virtual IRose* Create(string type)=0; 
//The factory create method in 90% of cases will take a parameter which 
//determines what kind of the object the factory will return.   
};

class Factory: public IFactory
{
public:
IRose* Create(string type)
{
    if ("Red" == type)
        return new RedRose();

    if ("Yellow" == type)
        return new YellowRose();

    return NULL;
}
};

int main()
{
IRose* p = NULL;
IFactory* f = NULL;

f = new Factory();  //You have to create an INSTANCE of the factory

p = f->Create("Red");
cout<<"\nColor is: "<<p->Color()<<"\n";
delete p;
p = f->Create("Yellow");
cout<<"\nColor is: "<<p->Color()<<"\n";
delete p;
return 1;
}

抽象工厂代码。

class IFridge
{
public:
virtual string Run(void) = 0;
};

class FridgeSamsung : public IFridge
{
public:
string Run(void)
{
    return "You are now running Samsung Fridge\n";
}
};

class FridgeWhirlpool : public IFridge
{
public:
string Run(void)
{
    return "You are now running Whirlpool Fridge\n";
}
};

class IWashingMachine
{
public:
virtual string Run(void) = 0;
};

class WashingMachineSamsung : public IWashingMachine
{
public:
string Run(void)
{
    return "You are now running Samsung Washing Machine\n";
}
};

class WashingMachineWhirlpool : public IWashingMachine
{
public:
string Run(void)
{
    return "You are now running Whirlpool Washing Machine\n";
}
};

class IFactory
{
public:
virtual IFridge* GetFridge(void) = 0;
virtual IWashingMachine* GetWashingMachine(void) = 0;
};

class FactorySamsung : public IFactory
{
IFridge* GetFridge(void)
{
    return new FridgeSamsung();
}

IWashingMachine* GetWashingMachine(void)
{
    return new WashingMachineSamsung();
}
};

class FactoryWhirlpool : public IFactory
{
IFridge* GetFridge(void)
{
    return new FridgeWhirlpool();
}

IWashingMachine* GetWashingMachine(void)
{
    return new WashingMachineWhirlpool();
}
};

int main()
{
IFridge* fridge;    //Client just knows about fridge and washingMachine.
IWashingMachine* washingMachine; //and factory. He will write operations which
IFactory* factory; //work on fridges and washingMachines.

factory = new FactorySamsung; 
//This is the only place where the client
//has to make a choice. 

//The rest of the code below will remain same, even 
//if the factory is changed. He can change the factory and the same range
//of products but from a different factory will be returned. No need to 
//change any code.

fridge = factory->GetFridge();
cout << fridge->Run();
washingMachine = factory->GetWashingMachine();
cout << washingMachine->Run();
cout << "\n";

delete factory;
factory = new FactoryWhirlpool;

//See same client code.
fridge = factory->GetFridge();
cout << fridge->Run();
washingMachine = factory->GetWashingMachine();
cout << washingMachine->Run();
cout << "\n";
delete factory;
return 1;
}

Answer 1

这是经过深思熟虑后修改的回复。

工厂方法:通常，createObject()是Creator对象的一个​​方法。

抽象工厂:通常工厂对象是Creator对象的一个​​属性。

现在假设 createObject() 和 Factory Object 属于它们各自的 Creator。

工厂方法:createObject() 可能会在 Creator 的子类中发生变化。这是通过通过继承更改 creatObject() 的实现来实现的。

Abstract Factory:Factory Object 也可能在 Creator 的子类中发生变化。然而，这种变化是通过用不同的工厂对象替换一个工厂对象来实现的，即 Creator 对象被组合改变了。

在您的演示中，creatObject() 和 Factory Object 在 Creator(s) 之外，因此模糊了组合/继承之间的区别!

Christopher Okhravi 在 YouTube 上有很棒的模式视频。

工厂方法 https://www.youtube.com/watch?v=EcFVTgRHJLM&index=4&list=PLrhzvIcii6GNjpARdnO4ueTUAVR9eMBpc

抽象工厂https://www.youtube.com/watch?v=v-GiuMmsXj4&index=5&list=PLrhzvIcii6GNjpARdnO4ueTUAVR9eMBpc

这里要求的是工厂方法的一个版本(这次是在 C++ 中!)。如果您需要任何口译帮助，请告诉我。

class IRose
{
public:
    virtual const char * Color(void) = 0;
};

class RedRose : public IRose
{
public:
    const char * Color(void)
    {
        return "I am a Red rose";
    }
};

class YellowRose : public IRose
{
public:
    const char * Color(void)
    {
        return "I am a Yellow rose";
    }
};

class RoseGarden
{
protected: class IRose* rose;   // a pointer to the garden's rose

public:
    virtual void createRose() { }  // abstract Factory Method

public: void sayColor() {
        cout << rose->Color() << '\n';
    }
};

class RedRoseGarden : public RoseGarden
{
public:
    void createRose()
    {
        this->rose = new RedRose();   // concrete factory method
    }
};

class YellowRoseGarden : public RoseGarden
{
public:
    void createRose()
    {
        this->rose = new YellowRose();  // concrete factory method
    }
};

int main()
{
    RoseGarden * garden = NULL;

    garden = new YellowRoseGarden;
    garden->createRose();      // correct factory method is chosen via inheritance
    garden->sayColor();
    delete garden;

    garden = new RedRoseGarden;
    garden->createRose();      // correct factory method is chosen via inheritance
    garden->sayColor();
    delete garden;

    return 1;
}

这里还有一个稍微修改过的抽象工厂版本，以更好地展示它是如何使用的。刚刚添加了一个房子对象。请注意，我为我的编译器将所有“字符串”对象更改为 const char*。

// make different types of fridges
class IFridge
{
public:
    virtual const char* Run(void) = 0;
};

class FridgeSamsung : public IFridge
{
public:
    const char* Run(void)
    {
        return "This house has a Samsung Fridge\n";
    }
};

class FridgeWhirlpool : public IFridge
{
public:
    const char* Run(void)
    {
        return "This house has a Whirlpool Fridge\n";
    }
};

// make different types of washing machine 
class IWashingMachine
{
public:
    virtual const char*  Run(void) = 0;
};

class WashingMachineSamsung : public IWashingMachine
{
public:
    const char* Run(void)
    {
        return "This house has a Samsung Washing Machine\n";
    }
};

class WashingMachineWhirlpool : public IWashingMachine
{
public:
    const char* Run(void)
    {
        return "This house has a Whirlpool Washing Machine\n";
    }
};

// make different type of factory
class IFactory
{
public:
    virtual IFridge* GetFridge(void) = 0;
    virtual IWashingMachine* GetWashingMachine(void) = 0;
};

class FactorySamsung : public IFactory
{
    IFridge* GetFridge(void)
    {
        return new FridgeSamsung();
    }

    IWashingMachine* GetWashingMachine(void)
    {
        return new WashingMachineSamsung();
    }
};

class FactoryWhirlpool : public IFactory
{
    IFridge* GetFridge(void)
    {
        return new FridgeWhirlpool();
    }

    IWashingMachine* GetWashingMachine(void)
    {
        return new WashingMachineWhirlpool();
    }
};

// Make a house object that has a fridge and a washing machine
class House
{
private:
    class  IWashingMachine * washingMachine;
    class  IFridge * fridge;

public:
    House(IFactory * houseFactory) {
        washingMachine = houseFactory->GetWashingMachine();
        fridge = houseFactory->GetFridge();
    }
    void showAppliances() {
        cout << washingMachine->Run();
        cout << fridge->Run();
    }
};

int main()
{
    class IFactory * factory;  
    class House * house;       

    // make a samsung house
    factory = new FactorySamsung;
    house = new House(factory);     // passing the factory by injection
    house->showAppliances();        // now we have a Samsung house
    cout << '\n';

    // clean up
    delete house;
    delete factory;

    // make a whirlpool house
    factory = new FactoryWhirlpool;
    house = new House(factory);    // passing the factory by injection
    house->showAppliances();       // now we have a WHilepool house
    cout << '\n';

    // clean up
    delete house;
    delete factory;

    return 1;
}