[结构型模式] head first 设计模式之工厂模式(Factory)

1 概述
  工厂模式专门负责将大量有共同接口的类实例化。工厂模式可以动态决定将哪一个类实例化，不必事先知道每次要实例化哪一个类。工厂模式有以下几种形态：
  a) 简单工厂(Simple Factory)模式
  专门定义一个类来负责创建其它类的实例，被创建的实例通常都具有共同的父类。
  注意：简单工厂模式并不包含在23种模式之内。

  b) 工厂方法(Factory Method)模式,又称多形性工厂(Polymorphic Factory)模式
  将对象的创建交由父类中定义的一个标准方法来完成，而不是其构造函数，究竟应该创建何种对象由具体的子类负责决定。 通过继承来实现的。

  c) 抽象工厂(Abstract Factory)模式,又称工具箱(Kit或Toolkit)模式
  提供一个共同的接口来创建相互关联的多个对象。 通过组合来实现的，但是抽象工厂中创建产品的方法通常是以“工厂方法”来实现的

GOF在《设计模式》一书中将工厂模式分为两类：工厂方法模式（Factory Method）与抽象工厂模式（Abstract Factory）。将简单工厂模式（Simple Factory）看为工厂方法模式的一种特例，两者归为一类。

2 说明
  工厂方法用来处理对象的创建，并将这样的行为封装在子类中。这样，客户程序中关于超类的代码就和子类对象创建代码解耦了。
  工厂模式定义：实例化对象，用工厂方法代替new操作。


简单工厂代码示例

class Light
{
public:
    virtual void TurnOn() = 0;
    virtual void TurnOff() = 0;
};

class BulbLight : public Light
{
public:
    virtual void TurnOn()
    {
        cout << "Bulb Light is Turned on\n";
    }

    virtual void TurnOff()
    {
        cout << "Bulb Light is Turned off\n";
    }
};

class TubeLight : public Light
{
public:
    virtual void TurnOn()
    {
        cout << "Tube Light is Turned on\n";
    }

    virtual void TurnOff()
    {
        cout << "Tube Light is Turned off\n";
    }
};

typedef enum EM_LightType
{
    LightType_Bulb,
    LightType_Tube,
}LightType;

class LightSimpleFactory
{
public:
    Light* Create(LightType emLightType)
    {
        if(LightType_Bulb == emLightType)
        {
            return new BulbLight();
        }
        else if(LightType_Tube == emLightType)
        {
            return new TubeLight();
        }
        else
        {
            return NULL;
        }
    }
};

class LightSimpleFactoryTest
{
public:
    void run()
    {
        LightSimpleFactory* pFactory = new LightSimpleFactory();

        Light* pLight = pFactory->Create(LightType_Bulb);
        pLight->TurnOn();
        pLight->TurnOff();
        delete pLight;

        cout <<"-----------------\n";

        pLight = pFactory->Create(LightType_Tube);
        pLight->TurnOn();
        pLight->TurnOff();
        delete pLight;

        delete pFactory;
    }
};

工厂方法示例

#ifndef   FACTORY_H
#define   FACTORY_H

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

//工厂模式
namespace Factory
{
//const definitions
////////////////////////////////////////////////////////////////////////// 
typedef list<string>  ToppingList;

//////////////////////////////////////////////////////////////////////////
class Pizza
{
public:
    const char* getName()
    {
        return m_Name.c_str();
    }

    void prepare()
    {
//         class PizzaIngredientFactory
//         {
//         public:
//             Dough* creatDough() { return new Dough(); }
//             Sauce* creatSauce() { return new Sauce(); }
//         };
//         PizzaIngredientFactory ingredientFactory;
//         
//         m_Dough = ingredientFactory.creatDough();
//         m_Sauce = ingredientFactory.creatSauce();

        cout << "Preparing " << m_Name.c_str() << endl;
        cout << "Tossing dough..." << endl;
        cout << "Adding sauce..." << endl;
        cout << "Adding topping: " << endl;

        ToppingList::const_iterator iter = m_Toppings.begin();
        ToppingList::const_iterator end  = m_Toppings.end();
        for ( ; iter !=  end; ++iter)
        {
            cout << " " << (*iter).c_str();
        }
        cout << endl;
    }

    void bake()
    {
        cout << "Bake for 25 minutes at 350" << endl;
    }

    void cut()
    {
        cout << "Cutting the pizza into diagonal slices" << endl;
    }

    void box()
    {
        cout << "Place pizza in official PizzaStore box" << endl;
    }

protected:
    string m_Name;
    string m_Dough;
    string m_Sauce;
    ToppingList m_Toppings;
};

//////////////////////////////////////////////////////////////////////////
class NYStyleCheesePizza : public Pizza
{
public:
    NYStyleCheesePizza()
    {
        m_Name  = "NY Style Sauce and cheese Pizza";
        m_Dough = "Thin Crust Dough";
        m_Sauce = "Marinara Sauce";
        m_Toppings.push_back(string("Grated Reggiano Cheese"));
    }
};

//////////////////////////////////////////////////////////////////////////
class ChicagoStyleCheesePizza : public Pizza
{
public:
    ChicagoStyleCheesePizza()
    {
        m_Name  = "Chicago Style Deep Dish cheese Pizza";
        m_Dough = "Extra Thick Crust Dough";
        m_Sauce = "Plum Tomato Sauce";

        m_Toppings.push_back(string("Shredded Mozzarella Cheese"));
    }

    void cut()
    {
        cout << "Cutting the pizza into square slices" << endl;
    }
};

//////////////////////////////////////////////////////////////////////////
class PizzaStore
{
public:
    Pizza* orderPizza( string type)
    {
        if (m_Pizza != NULL)
        {
            delete m_Pizza;
            m_Pizza = NULL;
        }

        m_Pizza = createPizza(type);

        if ( m_Pizza != NULL)
        {
            m_Pizza->prepare();
            m_Pizza->bake();
            m_Pizza->cut();
            m_Pizza->box();
        }

        return m_Pizza;
    }

    PizzaStore()
        : m_Pizza(NULL)
    {}

    virtual ~PizzaStore()
    {
        if (m_Pizza!=NULL)
        {
            delete m_Pizza;
            m_Pizza = NULL;
        }
    }

protected:
    virtual Pizza* createPizza(string type) = 0;

protected:
    Pizza* m_Pizza;
};

//the factory
//////////////////////////////////////////////////////////////////////////
class NYStylePizzaStore : public PizzaStore
{
public:
    virtual Pizza* createPizza(string type)
    {
        if (type == "cheese")
        {
            m_Pizza = new NYStyleCheesePizza();
        }
        else if (type == "pepperoni")
        {
            //m_Pizza = new NYStylePepperoniPizza();
        }
        else if (type=="clam")
        {
            //m_Pizza = new NYStyleClamPizza();
        }
        else if (type=="veggie")
        {
            //m_Pizza = new NYStyleVeggiePizza();
        }
        else
        {
            m_Pizza = NULL;
        }

        return m_Pizza;
    }
};

//////////////////////////////////////////////////////////////////////////
class ChicgoStytlePizzaStore : public PizzaStore
{
public:
    virtual Pizza* createPizza(string type)
    {
        if (type == "cheese")
        {
            m_Pizza = new ChicagoStyleCheesePizza();
        }
        else if (type == "pepperoni")
        {
            //m_Pizza = new ChicagoStylePepperoniPizza();
        }
        else if (type=="clam")
        {
            //m_Pizza = new ChicagoStyleClamPizza();
        }
        else if (type=="veggie")
        {
            //m_Pizza = new ChicagoStyleVeggiePizza();
        }
        else
        {
            m_Pizza = NULL;
        }
        
        return m_Pizza;
    }
};

//////////////////////////////////////////////////////////////////////////
class PizzaTestDrive
{
public:
    void run()
    {
        PizzaStore* nyStore = new NYStylePizzaStore();
        PizzaStore* chicagoStore = new ChicgoStytlePizzaStore();

        Pizza* pizza = nyStore->orderPizza("cheese");
        assert(pizza != NULL);
        cout << "Ethan ordered a " << pizza->getName() << endl;

        pizza = chicagoStore->orderPizza("cheese");
        assert(pizza != NULL);
        cout << "Joel ordered a " << pizza->getName() << endl;

        delete nyStore;
        delete chicagoStore;
    }
};

}//namespace Factory

#endif

抽象工厂示例

#include <iostream>
using namespace std;

class AbstractProductA
{
public:
    virtual ~AbstractProductA(){}

protected:
    AbstractProductA(){}

private:
};

class AbstractProductB
{
public:
    virtual ~AbstractProductB(){}

protected:
    AbstractProductB(){}
};

class ProductA1 : public AbstractProductA
{
public:
	ProductA1()
    {
        cout<<"ProductA1..."<<endl;
    }
    ~ProductA1(){}
};

class ProductA2 : public AbstractProductA
{
public:
	ProductA2()
    {
        cout<<"ProductA2..."<<endl;
    }

    ~ProductA2(){}
};

class ProductB1 : public AbstractProductB
{
public:
	ProductB1()
    {
        cout<<"ProductB1..." << endl;
    }
    ~ProductB1(){}
};

class ProductB2 : public AbstractProductB
{
public:
	ProductB2()
    {
        cout<<"ProductB2..." << endl;
    }
    ~ProductB2(){}
};

//////////////////////////////////////////////////////////////////////////
class AbstractFactory
{
public:
    virtual ~AbstractFactory(){}
	virtual AbstractProductA *CreateProductA() = 0;
	virtual AbstractProductB *CreateProductB() = 0;

protected:
    AbstractFactory(){}

};

class ConcreteFactory1 : public AbstractFactory
{
public:
	ConcreteFactory1()
    {
    }

	~ConcreteFactory1()
    {
    }

	AbstractProductA* CreateProductA()
    {
        return new ProductA1();
    }

	AbstractProductB* CreateProductB()
    {
        return new ProductB1();
    }
};

class ConcreteFactory2 : public AbstractFactory
{
public:
    ConcreteFactory2(){}
    ~ConcreteFactory2(){}

	AbstractProductA *CreateProductA()
    {
        return new ProductA2();
    }

	AbstractProductB *CreateProductB()
    {
        return new ProductB2();
    }
};

//////////////////////////////////////////////////////////////////////////
int main(int argc, char *argv[])
{
	AbstractFactory *cf1 = new ConcreteFactory1();
	cf1->CreateProductA();
	cf1->CreateProductB();

	AbstractFactory *cf2 = new ConcreteFactory2();
	cf2->CreateProductA();
	cf2->CreateProductB();

	return 0;
}