工厂模式（C++）

news2024/9/24 15:18:50

定义

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使得一个类的实例化延迟(目的:解耦，手段:虚函数)到子类。

应用场景

在软件系统中，经常面临着创建对象的工作;由于需求的变化，需要创建的对象的具体类型经常变化。
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具体对象创建工作的紧耦合?

结构

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代码示例

//Factory.h
/****************************************************/
#ifndef FACTORY_H
#define FACTORY_H
#include<iostream>
using namespace std;

class Shape
{
public:
	Shape() {};
	virtual ~Shape() {};
	virtual void draw() = 0;
 
	enum Shape_type{ Rectangle , Square, Circle};
};
 
class Rectangle :Shape
{
public:
	Rectangle() {};
	~Rectangle() {};
	void draw() { cout << "Inside Rectangle::draw() method." << endl; };
};
 
class Square :Shape
{
public:
	Square() {};
	~Square() {};
	void draw() { cout << "Inside Square::draw() method." << endl; };
};
 
class Circle :Shape
{
public:
	Circle() {};
	~Circle() {};
	void draw() { cout << "Inside Circle::draw() method." << endl; };
};
 
 
class ShapeFactory
{
public:
	ShapeFactory() {};
	~ShapeFactory() {};
 
	Shape* getShapeFactory(Shape::Shape_type type);
};
 
 
Shape* ShapeFactory::getShapeFactory(Shape::Shape_type type)
{
	switch (type)
	{
	case Shape::Rectangle:
		return (Shape*)new Rectangle();
	case Shape::Square:
		return (Shape*)new Square();
	case Shape::Circle:
		return (Shape*)new Circle();
	default:
		return NULL;
	}
}

#endif

//test.cpp
/****************************************************/
#include <iostream>
#include <string>
#include "Factory.h"
int main()
{
	ShapeFactory shapefac;
	Shape *t1 =(Shape*) shapefac.getShapeFactory(Shape::Circle);
	Shape *t2 = (Shape*)shapefac.getShapeFactory(Shape::Circle);
	Shape *t3 = (Shape*)shapefac.getShapeFactory(Shape::Circle);
 
	t1->draw();
	t2->draw();
	t3->draw();
 
	delete t1;
	t1 = NULL;
 
	delete t2;
	t2 = NULL;
 
	delete t3;
	t3= NULL;
	
	return 0;
}