简单工程模式

代码实现 

//simpleFactory.h
#ifndef _SimpleFactory_H_
#define _SimpleFactory_H_

#include <iostream>
#include <exception>
#include <string>

using namespace std;

class Operation {
protected:
    double _numberA = 0;
    double _numberB = 0;
public:
    Operation() {}
    Operation(double a, double b) {
        _numberA = a;
        _numberB = b;
    }
    Operation& operator=(Operation& p) {
        _numberA = p.getNumberA();
        _numberB = p.getNumberB();
    }
    double getNumberA() {
        return _numberA;
    }
    void setNumberA(double value) {
        _numberA = value;
    }
    double getNumberB() {
        return _numberB;
    }
    void setNumberB(double value) {
        _numberB = value;
    }
    virtual double GetResult() {
        return 0;
    }
};
class OperationAdd :public Operation {
    double GetResult() {
        double result = 0;
        result = _numberA + _numberB;
        return result;
    }
};
class OperationSub :public Operation {
    double GetResult() {
        double result = 0;
        result = _numberA - _numberB;
        return result;
    }
};
class OperationMul :public Operation {
    double GetResult() {
        double result = 0;
        result = _numberA * _numberB;
        return result;
    }
};
class OperationDiv :public Operation {
    double GetResult() {
        double result = 0;
        try {
            result = _numberA / _numberB;
        }
        catch (exception&) {
            cout << "发生除0异常" << endl;
        }
        return result;
    }
};
class OperationFactory {
public:
    static Operation* createOperation(char operate) {
        Operation* oper;
        switch (operate) {
        case '+':
            oper = new OperationAdd();
            break;
        case '-':
            oper = new OperationSub();
            break;
        case '*':
            oper = new OperationMul();
            break;
        case '/':
            oper = new OperationDiv();
            break;
        }
        return oper;
    }
};
#endif //_SimpleFactory_H_

UML图

总结

可以发现，简单工厂类是制造运算类的对象的，并且只需要传递关键参数给简单工厂类的方法（通常为静态方法），就可以创造出相应的对象出来。
故简单工厂适用于工厂类负责创建的对象较少的场景，且客户端只需要传入工厂类的参数，对于如何创建对象不需要关心。

收获

1.可以通过封装、继承、多态把程序的耦合度降低。
2.可以通过设计模式使程序变得更加灵活，易于修改，并且易于复用。
3.简单工厂模式适用创建对象少的情况，需要传参来指定需要的对象（产品）。