作用:
定义一个用于创建对象的接口,让子类决定实例化哪一个类。Factory Method 使一个类的实例化延迟到其子类。
UML结构图:

抽象基类:
1)Product:创建出来的对象的抽象基类.
2)Factory创建对象的工厂方法的抽象基类.
接口函数:
1)Creator::FactoryMethod:纯虚函数,由派生类实现,创建出对应的Product.
解析:
在这个模式中,有两个抽象基类,一个是Product为创建出来的对象的抽象基类,一个是Factory是工厂的抽象基类,在互相协作的时候都是由相应的Factory派生类来生成Product的派生类,也就是说如果要新增一种Product那么也要对应的新增一个Factory,创建的过程委托给了这个Factory.也就是说一个Factory和一个Product是一一对应的关系.
备注:
设计模式的演示图上把Factory类命名为Creator,下面的实现沿用了这个命名.
演示实现:
1)Factory.h

/**//********************************************************************
created: 2006/06/30
filename: Factory.h
author: 李创
http://www.cppblog.com/converse/

purpose: Factory模式的演示代码
*********************************************************************/

#ifndef FACTORY_H
#define FACTORY_H

class Product


{
public:

Product()
{}

virtual ~Product()
{}
};

class ConcreateProduct
: public Product


{
public:
ConcreateProduct();
virtual ~ConcreateProduct();
};

class Creator


{
public:

Creator()
{}

virtual ~Creator()
{}

void AnOperation();

protected:
virtual Product* FactoryMethod() = 0;
};

class ConcreateCreator
: public Creator


{
public:
ConcreateCreator();
virtual ~ConcreateCreator();

protected:
virtual Product* FactoryMethod();
};

#endif

2)Factory.cpp

/**//********************************************************************
created: 2006/06/30
filename: Factory.cpp
author: 李创
http://www.cppblog.com/converse/

purpose: Factory模式的演示代码
*********************************************************************/
#include "Factory.h"
#include <iostream>

using namespace std;

ConcreateProduct::ConcreateProduct()


{
std::cout << "construction of ConcreateProduct\n";
}

ConcreateProduct::~ConcreateProduct()


{
std::cout << "destruction of ConcreateProduct\n";
}

void Creator::AnOperation()


{
Product* p = FactoryMethod();

std::cout << "an operation of product\n";
}

ConcreateCreator::ConcreateCreator()


{
std::cout << "construction of ConcreateCreator\n";
}

ConcreateCreator::~ConcreateCreator()


{
std::cout << "destruction of ConcreateCreator\n";
}

Product* ConcreateCreator::FactoryMethod()


{
return new ConcreateProduct();
}

3)Main.cpp(测试代码)

/**//********************************************************************
created: 2006/06/30
filename: Main.cpp
author: 李创
http://www.cppblog.com/converse/

purpose: 测试Factory模式的代码
*********************************************************************/

#include "Factory.h"
#include <stdlib.h>

int main(int argc,char* argv[])


{
Creator *p = new ConcreateCreator();
p->AnOperation();

delete p;

system("pause");

return 0;
}


