工厂方法模式

理论

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起子类。

简单工厂 VS 工厂方法

相同点：它们都是集中封装了对象的创建，使得要更换对象时，不需要做大的改动就可以实现，降低了客户程序与产品对象的耦合。

简单工厂模式

　　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。

　　缺点：如果需要加一个新的功能，需要在工厂类的方法里添加Case的分支条件，违背了开放-封闭原则。

工厂方法模式

　　优点：是简单工厂模式的进一步抽象和推广，克服了简单工厂违背开放-封闭原则的缺点，又保持了封装对象创建过程的优点

　　缺点：每增加一个产品，需要加一个产品工厂的类，增加了额外的开发量。

工厂方法模式实现时，客户端需要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。也就是说，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。

实例1

用任意一种面向对象语言实现一个计算器控制台程序

UML类图

简单工厂模式

 工厂方法模式

 实现代码

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#include <iostream> #include <string> using namespace std;   //抽象运算类 class Operation{ public:     void GetNumber(int num1, int num2)     {         number_A = num1;         number_B = num2;     }       virtual int GetResult() = 0;   protected:     int number_A = 0;     int number_B = 0; };   //具体运算类 class OperationAdd :public Operation{ public:     int GetResult()     {         return number_A + number_B;     } };   class OperationSub :public Operation{ public:     int GetResult()     {         return number_A - number_B;     } };   class OperationMul :public Operation{ public:     int GetResult()     {         return number_A * number_B;     } };   class OperationDiv :public Operation{ public:     int GetResult()     {         if (number_B == 0)         {             cout << "除数不能为0" << endl;             exit(0);         }         return number_A / number_B;     } };   //简单工厂类 class OperationFactory { public:     static Operation* cerateOperate(char operate)     {         switch (operate)         {         case('+'):             return new OperationAdd;         case('-'):             return new OperationSub;         case('*'):             return new OperationMul;         case('/'):             return new OperationDiv;         default:             break;         }     } };   //抽象运算工厂类-->开闭原则: 对扩展开发，对修改关闭！！ class AbstractFactory { public:     virtual Operation* cerateOperate() = 0; };   //加法类工厂 class AddFactory : public AbstractFactory { public:     Operation* cerateOperate()     {         return new OperationAdd();     } };   //减法类工厂 class SubFactory : public AbstractFactory { public:     Operation* cerateOperate()     {         return new OperationSub();     } };   //乘法类工厂 class MulFactory : public AbstractFactory { public:     Operation* cerateOperate()     {         return new OperationMul();     } };   //除法类工厂 class DivFactory : public AbstractFactory { public:     Operation* cerateOperate()     {         return new OperationDiv();     } };   //客户端 void test01() {     int num1 = 5;     int num2 = 2;     int result = 0;     OperationFactory factory;     Operation* operate = factory.cerateOperate('-');     operate->GetNumber(num1, num2);     result = operate->GetResult();     cout << "num1 - num2 = " << result << endl;       delete operate; }   void test02() {     int num1 = 1;     int num2 = 2;     int result = 0;       AbstractFactory* factory = new AddFactory();     Operation* operate = factory->cerateOperate();     operate->GetNumber(num1, num2);     result = operate->GetResult();     cout << "num1 + num2 = " << result << endl;       delete operate;     delete factory; }   int main() {     test01();     test02();       system("pause");     return 0; }

实例2

学生/志愿者 以雷锋的名义做好事

实现代码

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#include <iostream> using namespace std;   //“雷锋”类 class Leifeng { public:     void Sweep()     {         cout << "扫地" << endl;     }       void Wash()     {         cout << "洗衣" << endl;     }       void BuyRice()     {         cout << "买米" << endl;     } };   //“学雷锋的大学生”类 class Undergraduate :public Leifeng {};   //“学雷锋的志愿者”类 class Volunteer :public Leifeng {};   //简单工厂类 class SimpleFactory { public:     static Leifeng* CreateLeifeng(int people)     {         Leifeng* result = NULL;         switch (people)         {         case(1):             result = new Undergraduate();             break;         case(2):             result = new Volunteer();             break;         }         return result;     } };   /*工厂方法模式*/   //雷锋工厂 class IFactory { public:     virtual Leifeng* CreatLeifeng() = 0; };   //学雷锋的大学生工厂 class UndergraduateFactory : public IFactory{ public:     Leifeng* CreatLeifeng()     {         return new Undergraduate();     } };   //社区志愿者工厂 class VolunteerFactory :public IFactory { public:     Leifeng* CreateLeifeng()     {         return new Volunteer();     } };   void test01() {     //简单工厂模式     Leifeng* studentA = SimpleFactory::CreateLeifeng(1); //三句重复的代码     studentA->BuyRice();     Leifeng* studentB = SimpleFactory::CreateLeifeng(1);     studentB->Sweep();     Leifeng* studentC = SimpleFactory::CreateLeifeng(1);     studentC->Wash(); }   void test02() {     //工厂方法模式     IFactory* factory = new UndergraduateFactory(); //如果要换成社区志愿者类只需修改此处     Leifeng* studentA = factory->CreatLeifeng();     Leifeng* studentB = factory->CreatLeifeng();     Leifeng* studentC = factory->CreatLeifeng();       studentA->BuyRice();     studentB->Sweep();     studentC->Wash();       delete factory;     delete studentA;     delete studentB;     delete studentC; }   int main() {     test01();     cout << "---------------------" << endl;     test02();       system("pause");     return 0; }