简单工厂模式

理论

简单工厂模式又叫静态方法模式（因为工厂类定义了一个静态方法）。现实生活中，工厂是负责生产产品的。同样在设计模式中，简单工厂模式我们可以理解为负责生产对象的一个类，称为“工厂类”。

作用：

将“类实例化的操作”与“使用对象的操作”分开，让使用者不用知道具体参数就可以实例化出所需要的类，从而避免了在客户端代码中显式指定，实现了解耦。

实例

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

 实现代码

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#include <iostream> #include <string> using namespace std;   class Operation { public:     void GetNumber(double num1, double num2)     {         number_A = num1;         number_B = num2;     }       virtual double GetResult() = 0;   protected:     double number_A;     double number_B; };   class OperationAdd :public Operation { public:     double GetResult()     {         return number_A + number_B;     } };   class OperationSub :public Operation { public:     double GetResult()     {         return number_A - number_B;     } };   class OperationMul :public Operation { public:     double GetResult()     {         return number_A * number_B;     } };   class OperationDiv :public Operation { public:     double GetResult()     {         if (number_B == 0)         {             cout << "除数不能为0" << endl;             exit(0);         }         return number_A / number_B;     } };   //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;         }     } };   void test() {     double num1, num2;     char choice;     cout << "请输入第一个数：" << endl;     cin >> num1;     cout << "您想进行的运算是：" << endl;     cin >> choice;     cout << "请输入第二个数：" << endl;     cin >> num2;       double result = 0;     OperationFactory factory;     Operation* operate = factory.cerateOperate(choice); //父类指针指向子类对象     operate->GetNumber(num1, num2);     result = operate->GetResult();     cout << "num1 " << choice << " num2 = " << result << endl;       delete operate; }   int main() {     test();       system("pause");     return 0; }