工厂方法模式

以下两种示例对于调用端来讲都需要知道具体的实例类型，例如需要知道哪个Creator实例，或者传递Type of Product Instance

UML类图

Alt text

代码示例

按照UML类图，代码如下：

#include "stdafx.h"
#include <iostream>
using namespace std;

class Product
{
public:
	virtual ~Product()
	{
	}
	virtual void Operation()
	{
		cout << "Product::Operation" << endl;
	}
};

class ConcreteProductA : public Product
{
public:
	virtual ~ConcreteProductA()
	{
	}
	virtual void Operation()
	{
		cout << "ConcreteProductA::Operation" << endl;
	}
};

class ConcreteProductB : public Product
{
public:
	virtual ~ConcreteProductB()
	{
	}
	virtual void Operation()
	{
		cout << "ConcreteProductB::Operation" << endl;
	}
};

class Creator
{
public:
	virtual Product* CreateConcreteProduct()
	{
		cout << "Creator::CreateConcreteProduct" << endl;
		return nullptr;
	}
};

class ConcreteCreatorA : public Creator
{
public:
	virtual Product* CreateConcreteProduct()
	{
		return new ConcreteProductA();
	}
};

class ConcreteCreatorB : public Creator
{
public:
	virtual Product* CreateConcreteProduct()
	{
		return new ConcreteProductB();
	}
};

int main()
{
	{
		ConcreteCreatorA objCCA;
		Product* pProduct = objCCA.CreateConcreteProduct();
		if (nullptr != pProduct)
		{
			pProduct->Operation();

			delete pProduct;
			pProduct = nullptr;
		}
	}

	system("pause");
	return 0;
}

也可以这样写：

Product* CreateConcreteProduct(int nType)
{
	switch (nType)
	{
	case 1:
	{
		return new ConcreteProductA();
	}
	case 2:
	{
		return new ConcreteProductB();
	}
	default:
		break;
	}
	return nullptr;
}

{
	Product* pProduct = CreateConcreteProduct(2);
	if (nullptr != pProduct)
	{
		pProduct->Operation();

		delete pProduct;
		pProduct = nullptr;
	}
}