抽象工厂模式（C++）

定义

提供一个接口,让该接口负责创建一系列“相关或者相互依赖的对象”，无需指定它们具体的类。

使用场景

• 在软件系统中，经常面临着“一系列相互依赖的对象”的创建工作;同时,由于需求的变化，往往存在更多系列对象的创建工作。
• 如何应对这种变化?如何绕过常规的对象创建方法(new)，提供一种“封装机制"来避免客户程序和这种“多系列具体对象创建工作”的紧耦合?

结构

代码示例

//AbstractFactory.h
/****************************************************/
#ifndef ABSTRACT_FACTORY_H
#define ABSTRACT_FACTORY_H
#include<iostream>
using namespace std;//形状抽象类接口shape
class shape
{
public:shape() {};virtual ~shape() {};virtual void draw() = 0;virtual double get_area() = 0;virtual void calculate_area() = 0;enum shape_type {rectangle,circle};protected:double area;
};//继承形状抽象接口的三角形类rectangle
class rectangle :shape
{
public:rectangle() { h = 2.5; k = 3.6; area = 0; };~rectangle() {};void draw();double get_area();void calculate_area();
private:double h;double k;
};	void rectangle::draw()
{cout << "draw rectangle class" << endl;
}double rectangle::get_area()
{return area;
}void rectangle::calculate_area()
{area = h*k / 2;
}//继承形状抽象接口的圆形类circle
class circle :shape
{
public:circle() { r = 4.8; area = 0; };~circle() {};void draw();double get_area();void calculate_area();
private:double r;
};void circle::draw()
{cout << "draw circle class" << endl;
}double circle::get_area()
{return area;
}void circle::calculate_area()
{area = 3.14*r*r;
}//颜色抽象类接口color
class color
{
public:color() {};virtual ~color() {};virtual void fill()=0;enum color_type { red, green };
};//继承颜色抽象类的红色类red
class red :color
{
public:red() {};~red() {};void fill() { cout << "fill red color" << endl; };
};//继承颜色抽象类的绿色类green
class green :color
{
public:green() {};~green() {};void fill() { cout << "fill green color" << endl; };
};//抽象类工厂abstractfactory
class abstractfactory
{
public:abstractfactory() {};virtual ~abstractfactory() {};virtual shape* getshape(shape::shape_type type)=0;virtual color* getcolor(color::color_type type)=0;enum factory_type{tshape,tcolor};
};//继承抽象工厂的形状工厂shapefactory
class shapefactory:abstractfactory
{
public:shapefactory() {};virtual ~shapefactory() {};shape* getshape(shape::shape_type type);color* getcolor(color::color_type type) { return NULL; };
};shape* shapefactory::getshape(shape::shape_type type)
{switch (type){case shape::rectangle:return (shape*)new rectangle();case shape::circle:return (shape*)new circle();default:return NULL;}
}//继承抽象工厂的颜色工厂colorfactory
class colorfactory :abstractfactory
{
public:colorfactory() {};virtual ~colorfactory() {};shape* getshape(shape::shape_type type) { return NULL; };color* getcolor(color::color_type type);
};color* colorfactory::getcolor(color::color_type type)
{switch (type){case color::red:return (color*)new red();case color::green:return (color*)new green();default:return NULL;}
}//工厂创造器类factoryproduct，通过传递颜色或形状信息来获取工厂
class factoryproduct
{
public:factoryproduct() {};~factoryproduct() {};abstractfactory* getfactory(abstractfactory::factory_type type);
};abstractfactory* factoryproduct::getfactory(abstractfactory::factory_type type)
{switch (type){case abstractfactory::tshape:return (abstractfactory*)new shapefactory();case abstractfactory::tcolor:return (abstractfactory*)new colorfactory();default:return NULL;}
}#endif

//test.cpp
/****************************************************/
#include <iostream>
#include <string>
#include "AbstractFactory.h"
int main()
{factoryproduct facput;abstractfactory *slfactory = facput.getfactory(abstractfactory::tshape);shape *k1 = slfactory->getshape(shape::rectangle);k1->draw();k1->calculate_area();cout << "area: " << k1->get_area() << endl;shape *k2 = slfactory->getshape(shape::circle);k2->draw();k2->calculate_area();cout << "area: " << k2->get_area() << endl;delete slfactory;slfactory = NULL;delete k1;k1 = NULL;delete k2;k2 = NULL;slfactory = facput.getfactory(abstractfactory::tcolor);color *k3 = slfactory->getcolor(color::red);k3->fill();color *k4 = slfactory->getcolor(color::green);k4->fill();delete slfactory;slfactory = NULL;delete k3;k3 = NULL;delete k4;k4 = NULL;return 0;
}

运行结果

要点总结

• 如果没有应对“多系列对象构建”的需求变化,则没有必要使用Abstract Factory模式,这时候使用简单的工广完全可以。
• “系列对象”指的是在某一特定系列下的对象之间有相互依赖、或作用的关系。不同系列的对象之间不能相互依赖。
• Abstract Factory模式主要在于应对“新系列”的需求变动。其缺点在于难以应对“新对象”的需求变动。