工厂模式

复习《大话设计模式》中的《工厂模式》

      工厂模式即实例化对象，即c++中new一个对象，其中运用面向对象继承，多态；降低了模块与模块的耦合度。

      书中的例子：

UML（unified modeling language）

示例代码：

#ifndef OPERATOR_H
#define OPERATOR_H
#include <cstring>
#include <QDebug>
/*抽象基类*/
class Operator
{
public:
        Operator(double n1 = 0, double n2 = 0);
        virtual double  getResult() = 0;
protected:
        
        double num1;
        double num2;
};
Operator::Operator(double n1, double n2)
{
        num1 = n1;
        num2 = n2;
};
/*子类*/
class Add:public Operator /*继承*/
{
public:
        Add(double n1, double n2):Operator(n1, n2){};
        double getResult();
};  
double Add::getResult()
{
        double temp = num1 + num2;
        return temp;
};
class Sub:public Operator
{
public:
        Sub(double n1, double n2):Operator(n1, n2){};
        double getResult();
};  
double Sub::getResult()
{
        double temp = num1 - num2;
        return temp;
};
class Multiple:public Operator
{
public:
        Multiple(double n1, double n2):Operator(n1, n2){};
        double getResult();
};  
double Multiple::getResult()
{
        double temp = num1 * num2;
        return temp;
};
class Divide:public Operator
{
public:
        Divide(double n1, double n2):Operator(n1, n2){};
        double getResult();
};  
double Divide::getResult()
{
        double temp = 0;
        if(num2 == 0)
        {
                throw num2;
                goto End;
        }
         temp = num1 / num2;
End:
        return temp;
};
/*工厂类*/
class Factory
{
public:
        Operator * createOperator(int operate, double n1 = 0, double n2 = 0);
    ~Factory();
protected:
    Operator *oper;
};
Factory::~Factory()
{
    if(oper != NULL)
        delete oper;
    oper = NULL;
}
/*实例化，返回基类指针*/
Operator * Factory::createOperator(int operate, double n1, double n2)
{
    oper = NULL;
        switch(operate)
        {
                case '+':
                        oper = new Add(n1, n2); /*多态oper指向Add类*/
                        break;
                case '-':
                        oper = new Sub(n1, n2);
                        break;
                case '*':
                        oper = new Multiple(n1, n2);
                        break;
                case '/':
                        oper = new Divide(n1, n2);
                        break;
                default:
                        oper = NULL;
        
        }
        return oper;
}
#endif