c – 检查对象类型的哪种方法更好？

发布时间：2020-12-16 03:41:54 所属栏目：百科来源：网络整理

导读：方法1： class Employee {public: virtual int calculateSalary() = 0;};class PermanentEmployee : public Employee { const int salaryPerMonth;public: PermanentEmployee(int sal) : salaryPerMonth(sal){} int calculateSalary() { return salaryPerMon

方法1：

class Employee 
{
public:
    virtual int calculateSalary() = 0;

};

class PermanentEmployee : public Employee {
    const int salaryPerMonth;
public:
    PermanentEmployee(int sal) : salaryPerMonth(sal){}

    int calculateSalary() {
        return salaryPerMonth;
    }
};

class ContractEmployee : public Employee {
    const int wagesPerHr;
    int totalHour;
public:
    ContractEmployee(int sal) : wagesPerHr(sal),totalHour(0){}

    void setWorkingDuration(int time) {
        totalHour = totalHour + time;
    }
    int calculateSalary() {
        return wagesPerHr * totalHour;
    }
};

class Manager {
    list<Employee *> ls;
public:
    void assignWorkingHour() {
        list<Employee *>::iterator it;

        for(it = ls.begin(); it != ls.end(); it++) {
            Employee *emp = *it;
            ContractEmployee* contractEmp = dynamic_cast<ContractEmployee* >(emp);
            if(contractEmp) {
                contractEmp->setWorkingDuration(5);
            }
        }
    }
};

在问题中,有两种类型的Employee：PermanentEmployee和ContractEmployee.
有一个名为Manager的类,其中包含在他下工作的所有员工的列表.
对于ContractEmployee,它必须调用函数setWorkingDuration(),该函数在类Manager的方法assignWorkingHour中调用.

问题是：
这里的Employee类型由dynamic_cast运算符确定,Manager必须知道Employee的所有类型的派生类.

方法2：

在类Employee中添加另一个成员：

enum TypeOfEmployee {CONTRACT,PERMANENT};

并检查TypeOfEmployee以确定Employee的类型

请告诉我哪个更好或有替代方法吗？

解决方法

更好的方法是编写不需要确切对象类型知识的代码.在我看来,处理这个问题最优雅的方法是将setWorkingDuration()移动到employee类.可能是这样的：

class Employee
{
public:
    // Calculates the salary for this employee.
    // Returns the calculated salary.
    virtual int calculateSalary() = 0;
    // Sets the working duration. Does nothing if the employee is permanent.
    // Returns true if Employee is on a contract,false if permanent.
    virtual bool setWorkingDuration(int time)
    {
        return false;
    }
};

class PermanentEmployee : public Employee
{
    const int salaryPerMonth;
public:
    PermanentEmployee(int sal) : salaryPerMonth(sal) {}

    int calculateSalary()
    {
        return salaryPerMonth;
    }
};

class ContractEmployee : public Employee
{
    const int wagesPerHr;
    int totalHour;
public:
    ContractEmployee(int sal) : wagesPerHr(sal),totalHour(0) {}

    int calculateSalary()
    {
        return wagesPerHr * totalHour;
    }

    bool setWorkingDuration(int time)
    {
        totalHour = totalHour + time;
        return true;
    }
};

class Manager
{
    list<Employee *> ls;
public:
    void assignWorkingHours()
    {
        list<Employee *>::iterator it;
        for(it = ls.begin(); it != ls.end(); it++)
        {
            Employee* emp = *it;
            emp->setWorkingDuration(5);
        }
    }
};

这样,Manager类不必知道Employee实际上是PermanentEmployee还是ContractEmployee.这就是多态性给你的东西.一般来说,如果您必须使用dynamic_cast<>,您可能需要再次查看设计并查看是否可以省略它.

（编辑：李大同）

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