C++ 学习笔记之 工厂模式 代码

简单工厂模式

客户端和具体实现类解耦。简单工厂模式，工厂并不符合开闭原则（每次都得修改工厂代码）。

简单工厂模式使用场景

工厂类负责创建的对象比较少，由于创建的对象较少，不会造成工厂方法中的业务逻辑太过复杂。客户端只知道传入工厂类的参数，对于创建对象不关心。

通过操作简单工厂类，让工厂类来new一个类。示例：

#include<iostream> //定义水果基类。//定义抽象水果 class AbstractFruit{ public: virtual void Showname()=0;//使用虚函数在这里，定义了一个方法 这个函数在水果里面被实例化 }; class Apple : public AbstractFruit{ //public 继承，原来 public 变成了public 原来的protected 变成了 protected、、、 按照优先级原则来 private> protected >public public: virtual void Showname(){ //实现之前定义的方法 std::cout<< "我是苹果"<< std::endl; } }; class Pear : public AbstractFruit{ public: virtual void Showname(){ std::cout<< "我是鸭梨"<< std::endl; } }; class Banana : public AbstractFruit{ public: virtual void Showname(){ std::cout<< "我是香蕉"<< std::endl; } }; //定义水果工厂 class FruitFactory{ public: static AbstractFruit* CreateFruit(std::string flag){ //返回一个抽象的类 if (flag == "apple"){ return new Apple; } else if(flag == "pear"){ return new Pear; } else if(flag == "banana"){ return new Banana; } } }; void test01(){ FruitFactory* factory = new FruitFactory; AbstractFruit* fruit = factory->CreateFruit("banana"); fruit->Showname(); delete fruit; fruit = factory->CreateFruit("apple"); fruit->Showname(); delete fruit; fruit = factory->CreateFruit("banana"); fruit->Showname(); delete fruit; fruit = factory->CreateFruit("pear"); fruit->Showname(); delete fruit; } int main(){ test01(); }

工厂方法模式

类的个数成倍增加，导致类越来越多。需要自己去判断创建哪一个类。创建过程延迟到了子类，实现了对象创建和分离，好处就是符合了开闭原则。

工厂方法模式 = 简单工厂模式 + 开闭原则

#include<iostream> //定义水果基类。//定义抽象水果 class AbstractFruit{ public: virtual void Showname()=0;//使用虚函数在这里，定义了一个方法 这个函数在水果里面被实例化 }; class Apple : public AbstractFruit{ //public 继承，原来 public 变成了public 原来的protected 变成了 protected、、、 按照优先级原则来 private> protected >public public: virtual void Showname(){ //实现之前定义的方法 std::cout<< "我是苹果"<< std::endl; } }; class Pear : public AbstractFruit{ public: virtual void Showname(){ std::cout<< "我是鸭梨"<< std::endl; } }; class Banana : public AbstractFruit{ public: virtual void Showname(){ std::cout<< "我是香蕉"<< std::endl; } }; //定义抽象工厂 class AbstractFruitFactory{ public: virtual AbstractFruit* CreateFruit() = 0; }; class AppleFactory: public AbstractFruitFactory{ virtual AbstractFruit* CreateFruit(){ return new Apple; } }; class BananaFactory: public AbstractFruitFactory{ virtual AbstractFruit* CreateFruit(){ return new Banana; } }; class PearFactory: public AbstractFruitFactory{ virtual AbstractFruit* CreateFruit(){ return new Pear; } }; void test01(){ //这里我有点疑问就是如果直接定义AbstractFruitFactory* factory = new BananaFactory; //好像后面再赋值 factory = new AppleFactory;会报错 这是什么原因呢。 AbstractFruitFactory* factory = NULL; AbstractFruit* fruit = NULL; factory = new BananaFactory; fruit = factory->CreateFruit(); fruit->Showname(); delete fruit; delete factory; factory = new AppleFactory; fruit = factory->CreateFruit(); fruit->Showname(); delete fruit; delete factory; factory = new PearFactory; fruit = factory->CreateFruit(); fruit->Showname(); delete fruit; delete factory; } int main(){ test01(); }

抽象工厂模式

先抽象产品等级 如：abstract apple；创建抽象类： class AbstractApple{ public: virtual void ShowName() = 0; }; 创建派生类： class CNApple : public AbstractApple{ public: virtual void ShowName(){ std::cout<<"中国苹果"<<endl; } }; 创建抽象工厂，针对产品族： class AbstractFactory{ public: virtual AbstractApple* CreateApple() = 0; } 创建派生工厂： class ChinaFactory: public AbstractFactory{ public: virtual AbstractApple* CreateApple(){ return new CNApple; } } 调用： void test(){ AbstractFactory* factory = NULL; AbstractApple* apple = NULL; factory = new ChinaFactory; apple = factory->CreateApple(); }

完整代码如下：

#include<iostream> //创建抽象类 class AbstractApple{ public: virtual void Showname()=0; }; class AbstractBanana{ public: virtual void Showname()=0; }; class AbstractPear{ public: virtual void Showname()=0; }; //创建派生类 class CNapple : public AbstractApple{ public: virtual void Showname(){ std::cout<<"Chinese apple"<<std::endl; } }; class CNbanana : public AbstractBanana{ public: virtual void Showname(){ std::cout<<"Chinese banana"<<std::endl; } }; class CNpear : public AbstractPear{ public: virtual void Showname(){ std::cout<<"Chinese pear"<<std::endl; } }; class USAapple : public AbstractApple{ public: virtual void Showname(){ std::cout<<"American apple"<<std::endl; } }; class USAbanana : public AbstractBanana{ public: virtual void Showname(){ std::cout<<"American banana"<<std::endl; } }; class USApear : public AbstractPear{ public: virtual void Showname(){ std::cout<<"American pear"<<std::endl; } }; class JPapple : public AbstractApple{ public: virtual void Showname(){ std::cout<<"Japanese apple"<<std::endl; } }; class JPbanana : public AbstractBanana{ public: virtual void Showname(){ std::cout<<"Japanese banana"<<std::endl; } }; class JPpear : public AbstractPear{ public: virtual void Showname(){ std::cout<<"Japanese pear"<<std::endl; } }; //创建抽象工厂，针对产品族 class AbstractFactory{ public: virtual AbstractApple* CreateApple() = 0; virtual AbstractBanana* CreateBanana() = 0; virtual AbstractPear* CreatePear() = 0; }; //创建派生 class ChinaFactory : public AbstractFactory{ public: virtual AbstractApple* CreateApple(){ return new CNapple; } virtual AbstractBanana* CreateBanana(){ return new CNbanana; } virtual AbstractPear* CreatePear(){ return new CNpear; } }; class AmericanFactory : public AbstractFactory{ public: virtual AbstractApple* CreateApple(){ return new USAapple; } virtual AbstractBanana* CreateBanana(){ return new USAbanana; } virtual AbstractPear* CreatePear(){ return new USApear; } }; class JapanFactory : public AbstractFactory{ public: virtual AbstractApple* CreateApple(){ return new JPapple; } virtual AbstractBanana* CreateBanana(){ return new JPbanana; } virtual AbstractPear* CreatePear(){ return new JPpear; } }; void test(){ AbstractFactory* factory = NULL; AbstractApple* apple = NULL; AbstractBanana* banana = NULL; AbstractPear* pear = NULL; factory = new ChinaFactory; //定义一个新工厂 apple = factory->CreateApple(); // factory 生产一个apple banana = factory->CreateBanana(); pear = factory->CreatePear(); apple->Showname(); banana->Showname(); pear ->Showname(); delete pear; delete banana; delete apple; delete factory; } int main(){ test(); return 0; }