大话设计模式 --- 简单工厂模式

        说的是简单的二元数学运算的问题：加减乘除等。

        书里是用非C++语言描述的，不过我还是喜欢C++多一点，下面改成了C++版。

        操作基类：

        class Operation:

         {

            public:

              Operation(): m_numA (0), m_numB(0){}

              virtual double GetResult(){return 0;}

              void setOperationNum( double numA,double numB )

              {

                     m_numA = numA;

                     m_numB = numB;

              }

            private:

              double m_numA;

              double m_numB;

         };

        加法类：

        class OperationAdd: public Operation

        {

             public:

               virtual double GetResult()

              {

                    return m_numA + m_numB;

              }

        }

        类似实现 减法类 OperationSub   乘法类 OperationMul 等

        再实现运算工厂类：

        class OperationFactory:

        {

             public:

                 Operation * createOperate( const string& operate )

                 {

                        Operation* oper;

                        switch(operate )

                        {

                               case "+": oper = new OperationAdd();break;

                               case "-": oper = new OperationSub();break;

                               ... ...

                        }

                 }

        }

        实际应用：

        Operation*oper;

        OperationFactory factory;

        oper = factory.createOperate("+");

        oper->setOperationNum(2,3);

        double result = oper->GetResult();

        delete  oper;