第八章 雷锋依然在人间---工厂方法模式(读书笔记)

一：简单工厂模式

简单工厂的UML图：

代码如下：

#include<iostream>  #include<string>  using std::cout;  using std::endl;  using std::cin;  using std::string;    //基类  class Operation  {  public:      Operation():m_numberA(0),m_numberB(0)      {      };      Operation(double numberA,double numberB):m_numberA(numberA),m_numberB(numberB)      {      };      double getA()      {          return m_numberA;      };      double getB()      {          return m_numberB;      };      void setA(double number)        {            m_numberA = number;        };        void setB(double number)        {            m_numberB = number;        };        virtual double GetResult()//多态性      {          return 0;      }  protected:      double m_numberA;      double m_numberB;  };    //加法类    class OperationAdd :public Operation //继承  {    public:        double GetResult()        {            double result = 0;            result = m_numberA + m_numberB;            return result;        }    };    //减法类    class OperationSub :public Operation    {    public:        double GetResult()        {            double result = 0;            result = m_numberA - m_numberB;            return result;        }    };    //乘法类    class OperationMul :public Operation    {    public:        double GetResult()        {            double result = 0;            result = m_numberA * m_numberB;            return result;        }    };    //除法类    class OperationDiv :public Operation    {    public:        double GetResult()        {            double result = 0;            if ( m_numberB == 0 )                throw "除数不能为0";            result = m_numberA / m_numberB;            return result;        }    };    //计算工厂设计模式  class OperationFactory  {  public:      static Operation* createOperate(char oper)  //封装      {          Operation* myOper=NULL;          switch (oper)          {          case '+':              myOper=new OperationAdd();              break;              case '-':                myOper = new OperationSub();                break;            case '*':                myOper = new OperationMul();                break;            case '/':                myOper = new OperationDiv();                break;            default:              break;          };          return myOper;      }  };    void main()  {      int operaterA,operaterB;      cout<<"请输入数字A"<<endl;      cin>>operaterA;      cout<<"请输入数字B"<<endl;      cin>>operaterB;      Operation* op=OperationFactory::createOperate('*');      op->setA(operaterA);      op->setB(operaterB);      cout<<operaterA<<" * "<<operaterB<<" 的结果为： "<<endl;      cout<<op->GetResult()<<endl;  }

工厂方法的UML：

本次程序的UML：

代码实现如下：

#include<iostream>

#include<string>using std::cout;using std::endl;using std::string;class 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;      }  };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();      };  };  int main()  {      IFactory* operFactory = new AddFactory();      Operation* oper = operFactory->CreateOperation();        oper->setA(1);      oper->setB(2);      double result = oper->GetResult();  cout<<result<<endl;    delete operFactory;      delete oper;      return 0;  }  

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。

抽象工厂的UML：