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
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 
#include 
#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。