工厂模式（C++）

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

在这里插入图片描述

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;
}