3.14 以子类取代类型码

【1】原代码

 1 class Employee
 2 {
 3 public:
 4     const static int ENGINEER = 0;
 5     const static int SALESMAN = 1;
 6     const static int MANAGER = 2;
 7 
 8 public:
 9     Employee();
10 
11     int payAmount()
12     {   // 典型的switch语句案例。
13         // 这里仅仅列出了一个函数的业务逻辑实现过程，实际中可能会有很多这样的函数，需要进行这样类似的条件判断
14         switch (m_nType)
15         {
16         case ENGINEER:
17             return m_monthlySalary;
18         case SALESMAN:
19             return m_monthlySalary + m_bonus;
20         case MANAGER:
21             return m_monthlySalary + m_commission;
22         default:
23             break;
24         }
25     }
26 
27 private:
28     int m_nType;
29     int m_bonus;
30     int m_commission;
31     int m_monthlySalary;
32 };

【2】以子类取代类型码

Employee.h

 1 #ifndef _EMPLOYEE_H
 2 #define _EMPLOYEE_H
 3 
 4 #include "EmployeeType.h"
 5 class Employee
 6 {
 7 public:
 8     Employee(int nType);
 9 
10     int getType();
11     void setType(int nType);
12     int payAmount();
13 
14 private:
15     EmployeeType *m_pType;
16 };
17 #endif

Employee.cpp

 1 #include "Employee.h"
 2 
 3 Employee::Employee(int nType)
 4 {
 5     setType(nType);
 6 }
 7 
 8 int Employee::getType()
 9 {
10     return m_pType->getTypeCode();
11 }
12 
13 void Employee::setType(int nType)
14 {
15     m_pType = EmployeeType::newType(nType);
16 }
17 
18 int Employee::payAmount()
19 {
20     return m_pType->payAmount();
21 }

EmployeeType.h

 1 #ifndef _EMPLOYEETYPE_H
 2 #define _EMPLOYEETYPE_H
 3 
 4 class EmployeeType
 5 {
 6 public:
 7     const static int ENGINEER = 0;
 8     const static int SALESMAN = 1;
 9     const static int MANAGER = 2;
10 
11 public:
12     EmployeeType();
13     static EmployeeType* newType(int code);
14 
15     virtual int payAmount() = 0;
16     virtual int getTypeCode() = 0;
17 
18 public:
19     int m_bonus;
20     int m_commission;
21     int m_monthlySalary;
22 };
23 
24 #endif

EmpolyeeeType.cpp

 1 #include "EmployeeType.h"
 2 #include "Engineer.h"
 3 #include "Manager.h"
 4 #include "Salesman.h"
 5 
 6 EmployeeType::EmployeeType()
 7     : m_bonus(1000)
 8     , m_commission(500)
 9     , m_monthlySalary(2000)
10 {}
11 
12 EmployeeType* EmployeeType::newType(int code)
13 {
14     switch (code)
15     {
16     case ENGINEER:
17         return (new Engineer());
18     case SALESMAN:
19         return (new Salesman());
20     case MANAGER:
21         return (new Manager());
22     default:
23         return (new Engineer());
24     }
25 }

Engineer.h

 1 #ifndef _ENGINEER_H
 2 #define _ENGINEER_H
 3 
 4 #include "EmployeeType.h"
 5 class Engineer : public EmployeeType
 6 {
 7 public:
 8     Engineer();
 9     int getTypeCode();
10     int payAmount();
11 };
12 
13 #endif

Engineer.cpp

 1 include "Engineer.h"
 2 
 3 Engineer::Engineer() : EmployeeType()
 4 {}
 5 
 6 int Engineer::getTypeCode()
 7 {
 8     return ENGINEER;
 9 }
10 
11 int Engineer::payAmount()
12 {
13     return m_monthlySalary;
14 }

Manager.h

 1 #ifndef _MANAGER_H
 2 #define _MANAGER_H
 3 
 4 #include "EmployeeType.h"
 5 
 6 class Manager : public EmployeeType
 7 {
 8 public:
 9     Manager();
10     int getTypeCode();
11     int payAmount();
12 };
13 
14 #endif

Manager.cpp

 1 #include "Manager.h"
 2 
 3 Manager::Manager() : EmployeeType()
 4 {}
 5 
 6 int Manager::getTypeCode()
 7 {
 8     return MANAGER;
 9 }
10 
11 int Manager::payAmount()
12 {
13     return m_monthlySalary + m_commission;
14 }

Salesman.h

 1 #ifndef _SALESAMAN_H
 2 #define _SALESAMAN_H
 3 
 4 #include "EmployeeType.h"
 5 
 6 class Salesman : public EmployeeType
 7 {
 8 public:
 9     Salesman();
10     int getTypeCode();
11     int payAmount();
12 };
13 
14 #endif

Salesman.cpp

 1 #include "Salesman.h"
 2 
 3 Salesman::Salesman() : EmployeeType()
 4 {}
 5 
 6 int Salesman::getTypeCode()
 7 {
 8     return SALESMAN;
 9 }
10 
11 int Salesman::payAmount()
12 {
13     return m_monthlySalary + m_bonus;
14 }

main.cpp

1 #include "Employee.h"
2 
3 void main()
4 {
5     Employee *pEngineer = new Employee(EmployeeType::ENGINEER);
6     pEngineer->payAmount();
7 }

【3】总结

有一个不可变的类型码，它会影响类的行为。以子类取代这个类型码。

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