大话设计模式--工厂方法模式 Factory Method -- C++实现

来源：互联网发布：linux aria2 编辑：程序博客网时间：2024/06/09 22:42

1. 工厂方法模式

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其子类。

和简单工厂模式相比：

A：简单工厂模式最大的优点在于工厂类中包含有必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对客户端来说去除了与具体产品的依赖。

但缺点是添加新产品时需要修改工厂类 case，违背了 "开放-封闭" 原则。

B：工厂方法模式实现时，需要由客户端来决定实例化哪一个工厂来实现运算类，选择判断的问题还是存在，只是由工厂类内部转移到客户端。

实例：

operation.h -- operation.cpp

#ifndef OPERATION_H#define OPERATION_Hclass Operation{public:    Operation();    double virtual getResult();    double strA;    double strB;    double result;};#endif // OPERATION_H

#include "operation.h"Operation::Operation(){    strA = 0;    strB = 0;    result = 0;}double Operation::getResult(){    return result;}

operationfunc.h operationfunc.cpp

#ifndef OPERATIONFUNC_H#define OPERATIONFUNC_H#include "operation.h"class OperationAdd : public Operation{public:    double getResult();};class OperationSub : public Operation{public:    double getResult();};class OperationMul : public Operation{public:    double getResult();};class OperationDiv : public Operation{public:    double getResult();};

#include "operationfunc.h"double OperationAdd::getResult(){    result = strA + strB;    return result;}double OperationSub::getResult(){    result = strA - strB;    return result;}double OperationMul::getResult(){    result = strA * strB;    return result;}double OperationDiv::getResult(){    result = strA / strB;    return result;}

factory.h factory.cpp 抽象工厂

#ifndef FACTORY_H#define FACTORY_H#include "operation.h"#include "operationfunc.h"#include <string>using namespace std;class Factory{public:    Factory();    virtual Operation* createOperation();};#endif // FACTORY_H

#include "factory.h"Factory::Factory(){}Operation* Factory::createOperation(){}

addfactory.h addfactory.cpp

#ifndef ADDFACTORY_H#define ADDFACTORY_H#include "factory.h"class AddFactory : public Factory{public:    AddFactory();    Operation* createOperation();};#endif // ADDFACTORY_H

#include "addfactory.h"AddFactory::AddFactory(){}Operation* AddFactory::createOperation(){    return new OperationAdd();}

subfactory.h subfactory.cpp

#ifndef SUBFACTORY_H#define SUBFACTORY_H#include "factory.h"class SubFactory : public Factory{public:    SubFactory();    Operation* createOperation();};#endif // SUBFACTORY_H

#include "subfactory.h"SubFactory::SubFactory(){}Operation* SubFactory::createOperation(){    return new OperationSub();}

main.cpp

#include <iostream>#include "operationfunc.h"#include "addfactory.h"#include "subfactory.h"using namespace std;int main(){    cout << "Factory method " << endl;    Factory *factory = new SubFactory();    Operation *oper = factory->createOperation();    oper->strA = 1.1;    oper->strB = 2.3;    cout << "result: " << oper->getResult() << endl;    return 0;}