第八章 雷锋依然在人间-工厂方法模式(读书笔记)

 雷锋依然在人间-工厂方法模式

1.简单工厂模式的最大优点在于工厂类中包含了必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对于客户端来说，去除了与具体产品的依赖。
2.工厂方法模式（Factory Method）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。工厂方法使一个类的实例化延迟到子类。
3.工厂方法模式的好处就是在扩展功能的时候，只要扩展了变化，不用修改现有的类了，也就完全符合了开放-封闭原则。
4.工厂方法把简单工厂的内部逻辑判断移到了客户端代码来进行。你想要加功能，搬来是改工厂类的，而现在是修改客户端。
5.工厂方法模式是简单工厂模式的进一步抽象和推广。由于使用了多态性，工厂方法模式保持了简单工厂模式的优点，而且克服了它的缺点。但缺点是由于每加一个产品，就需要加一个产品工厂的类，增加了额外的开发量。
6.老人不需要知道谁来做好事，他只需知道是学雷锋的人来帮忙就可以了。

8.1  Operation.h

#pragma onceclass Operation{public:Operation():m_numberA(0),m_numberB(0){};Operation(double numberA, double numberB):m_numberA(numberA),m_numberB(m_numberB){};double getA(){return m_numberA;};void setA(double number){m_numberA = number;};double getB(){return m_numberB;};void setB(double number){m_numberB = number;};virtual double GetResult(){return 0;}protected:double m_numberA;double m_numberB;};class OperationAdd :public Operation{public:double GetResult(){double result = 0;result = m_numberA + m_numberB;return result;}};class OperationSub :public Operation{public:double GetResult(){double result = 0;result = m_numberA - m_numberB;return result;}};class OperationMul :public Operation{public:double GetResult(){double result = 0;result = m_numberA * m_numberB;return result;}};class OperationDiv :public Operation{public:double GetResult(){double result = 0;if ( m_numberB == 0 )throw "被除数不能为零";result = m_numberA / m_numberB;return result;}};

8.2  IFactory.h

#pragma once #include "Operation.h"class IFactory{public:virtual Operation* CreateOperation(void) = 0;};//加法工厂class AddFactory :public IFactory{public:Operation* CreateOperation(void){return new OperationAdd();};};//减法工厂class SubFactory :public IFactory{public:Operation* CreateOperation(void){return new OperationSub();};};//乘法工厂class MulFactory :public IFactory{public:Operation* CreateOperation(void){return new OperationMul();};};//除法工厂class DivFactory :public IFactory{public:Operation* CreateOperation(void){return new OperationDiv();};};

8.3  客户端

#include "stdafx.h"#include "IFactory.h"int _tmain(int argc, _TCHAR* argv[]){IFactory* operFactory = new AddFactory();Operation* oper = operFactory->CreateOperation();oper->setA(1);oper->setB(2);double result = oper->GetResult();delete operFactory;delete oper;return 0;}