1. Recitation Course 0610
Speaker: Liu Yu-Jiun

2. Chap 12 Inheritance

3. Introduction Create new class from existing class
Absorb existing class’s data and behaviors
Enhance with new capabilities
Derived class inherits from base class
Derived class
More specialized group of objects
Behaviors inherited from base class
Can customize
Additional behaviors
Relationship
Composition: has a relationship
Inheritance: is a relationship

4. is-a Base class Derived class Direct base class Indirect base class
Base and derived
class
is-a
Base class
Derived class
Direct base class
Indirect base class

5. 12.2 base class and derived class
public inheritance:
Specify with:
class derived_class_name : public base_class_name
Example:
class TwoDimensionalShape : public Shape
Base class private members
Still inherited, but not accessible directly
Base class public and protected members
Inherited with original member access
friend function
Not inherited

6. 12.3 protected Members protected access Derived-class members
Intermediate level of protection between public and private
protected members are accessible to
Base class members
Base class friends
Derived class members
Derived class friends
Derived-class members
Refer to public and protected members of base class
Simply use member names
Redefined base class members can be accessed by using base-class name and binary scope resolution operator (::)
衍生類別如果想用基本類別中的public和protected成員，只要直接使用就好。
如果衍生類別重新定義了基本類別的成員(衍生類別有成員和基本類別成員的名稱相同，但是功能不同)，只要加上基本類別的名稱和::

7. 12.4 Relationship between Base Classes and Derived Classes
Five examples:
Class CommissionEmployee
Class BasePlusCommissionEmployee (v1)
Without inheritance
Class BasePlusCommissionEmployee (v2)
Inherit from class CommissionEmployee
Use private member in base class
Class BasePlusCommissionEmployee (v3)
Let private members be protected members in base class
Class BasePlusCommissionEmployee (v4)
Use public member function in base class to access private members in base class

8. 12.4.1 class CommissionEmployee

9. 5 pairs of set and get functions for accessing each data member
// Fig. 12.4: CommissionEmployee.h
#ifndef COMMISSION_H
#define COMMISSION_H
#include <string>
using namespace std;
class CommissionEmployee{
public:
CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);
void setFirstName(const string &);
string getFirstName() const;
void setLastName(const string &);
void setSocialSecurityNumber(const string &);
void setGrossSales(double);
double getFirstName() const;
void setCommissionRate(double);
double earnings() const;
void print() const;
private:
string firstName;
string lastName;
string socialSecurityNumber;
double grossSales;
double commissionRate; };
#endif
5 pairs of set and get functions for accessing each data member

10. 10
Outline
Commission Employee.cpp
(1 of 4)
Initialize data members 10

11. Outline (2 of 4) Function setGrossSales validates gross sales amount11
Outline
Commission Employee.cpp
(2 of 4)
Function setGrossSales validates gross sales amount 11

12. Outline Function setCommissionRate validates commission rate (3 of 4)12
Outline
Function setCommissionRate validates commission rate
Commission Employee.cpp
(3 of 4) 12

13. Outline Function earnings calculates earnings (4 of 4)13
Outline
Function earnings calculates earnings
Commission Employee.cpp
(4 of 4)
Function print displays CommissionEmployee object 13

14. Outline (1 of 2) Instantiate CommissionEmployee object14
Outline
fig12_06.cpp
(1 of 2)
Instantiate CommissionEmployee object
Use CommissionEmployee’s get functions to retrieve the object’s instance variable values 14

15. 15
Outline
Use CommissionEmployee’s set functions to change the object’s instance variable values
fig12_06.cpp
(2 of 2)
Call object’s print function to display employee information
Call object’s earnings function to calculate earnings 15

16. Class BasePlusCommissionEmployee16
Creating a BasePlusCommissionEmployee Class Without Using Inheritance
Class BasePlusCommissionEmployee
Much of the code is similar to CommissionEmployee
private data members
public methods
constructor
Additions
private data member baseSalary
Methods setBaseSalary and getBaseSalary 16

17. 17
Outline
BasePlus Commission Employee.h
(1 of 2)
Constructor takes one more argument, which specifies the base salary
與類別CommissionEmployee重複 17

18. Outline Define get and set functions for data member baseSalary18
Define get and set functions for data member baseSalary
Outline
BasePlus Commission Employee.h
(2 of 2)
Add data member baseSalary 18

19. 19
Outline
BasePlus Commission Employee.cpp
(1 of 4)
Constructor takes one more argument, which specifies the base salary
Use function setBaseSalary to validate data 19

20. 20
Outline
BasePlus Commission Employee.cpp
(2 of 4) 20

21. 21
Outline
BasePlus Commission Employee.cpp
(3 of 4) 21

22. 22
Outline
Function setBaseSalary validates data and sets instance variable baseSalary
BasePlus Commission Employee.cpp
(4 of 4)
Function getBaseSalary returns the value of instance variable baseSalary
Update function earnings to calculate the earnings of a base-salaried commission employee
Update function print to display base salary 22

23. Outline (1 of 3) Instantiate BasePlusCommissionEmployee object 23
fig12_09.cpp
(1 of 3)
Instantiate BasePlusCommissionEmployee object 23

24. 24
Outline
Use BasePlusCommissionEmployee’s get functions to retrieve the object’s instance variable values
fig12_09.cpp
(2 of 3)
Use BasePlusCommissionEmployee’s setBaseSalary function to set base salary
Call object’s print function to display employee information
Call object’s earnings function to calculate employee’s earnings 24

25. 25
Outline
fig12_09.cpp
(3 of 3) 25

26. 12.4.3 Creating a CommissionEmployee-BasePlusCommissionEmployee Inheritance Hierarchy
Class BasePlusCommissionEmployee
Derived from class CommissionEmployee
Is a CommissionEmployee
Inherits all public members
Constructor is not inherited
Use base-class initializer syntax to initialize base-class data member
Has data member baseSalary 26

27. Include the base-class header file in the derived-class header file:
Know that base class exist.
Know size of inherited data members.(併入衍生類別物件的總記憶體需求量)
Ensure that inherited class members are used properly.
Class BasePlusCommissionEmployee derives publicly from class CommissionEmployee 27

28. 在成員初始值列表初始化成員物件並明確的呼叫基本類別建構子，可以避免重複初始化的問題。
Initialize base class data member by calling the base-class constructor using base-class initializer syntax.
在成員初始值列表初始化成員物件並明確的呼叫基本類別建構子，可以避免重複初始化的問題。 28

29. Compiler generates errors because base class’s data member commissionRate and grossSales are private
Compiler generates errors because the base class’s data members firstName, lastName, socialSecurityNumber, grossSales and commissionRate are private 29

30. 30

31. 12.4.4 CommissionEmployee-BasePlusCommissionEmployee Inheritance Hierarchy Using protected Data
Use protected data
Enable class BasePlusCommissionEmployee to directly access base class data members
Base class’s protected members are inherited by all derived classes of that base class 31

32. CommissionEmployee.h相同
// Fig. 12.4: CommissionEmployee.h
#ifndef COMMISSION_H
#define COMMISSION_H
#include <string>
using namespace std;
class CommissionEmployee{
public:
CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);
void setFirstName(const string &);
string getFirstName() const;
void setLastName(const string &);
void setSocialSecurityNumber(const string &);
void setGrossSales(double);
double getFirstName() const;
void setCommissionRate(double);
double earnings() const;
void print() const;
private:
string firstName;
string lastName;
string socialSecurityNumber;
double grossSales;
double commissionRate; };
#endif
protected:
幾乎與12.4.1的
CommissionEmployee.h相同

33. CommissionEmployee.cpp完全相同33
Outline
Commission Employee.cpp
(1 of 3)
與12.4.1的
CommissionEmployee.cpp完全相同 33

34. CommissionEmployee.cpp完全相同34
Outline
Commission Employee.cpp
(2 of 3)
與12.4.1的
CommissionEmployee.cpp完全相同 34

35. CommissionEmployee.cpp完全相同35
Outline
Commission Employee.cpp
(3 of 3)
與12.4.1的
CommissionEmployee.cpp完全相同 35

36. BasePlusCommissionEmployee.h完全相同36
Outline
BasePlus Commission Employee.h
(1 of 1)
BasePlusCommissionEmployee still inherits publicly from CommissionEmployee
與12.4.3的
BasePlusCommissionEmployee.h完全相同 36

37. BasePlusCommissionEmployee.cpp完全相同37
Outline
BasePlus Commission Employee.cpp
(1 of 2)
Call base-class constructor using base-class initializer syntax
與12.4.3的
BasePlusCommissionEmployee.cpp完全相同 37

38. BasePlusCommissionEmployee.cpp完全相同38
Outline
BasePlus Commission Employee.cpp
(2 of 2)
Directly access base class’s protected data
與12.4.3的
BasePlusCommissionEmployee.cpp完全相同 38

39. 39
Outline
Fig12_16.cpp
(1 of 2) 39

40. 40
Outline
Fig12_16.cpp
(2 of 2)
與12.4.2的程式功能相同，
但是程式碼變短，也比較容易維護 40

41. 41
CommissionEmployee-BasePlusCommissionEmployee Inheritance Hierarchy Using protected Data (Cont.)
Advantages
Derived class can modify values directly
Avoid set/get method call overhead
Slight increase in performance
Disadvantages
No validity checking
Derived class can assign illegal value
Implementation dependent
Derived class functions more likely dependent on base class implementation
Base class implementation changes may result in derived class modifications
Fragile (brittle) software 41

42. 12.4.5 CommissionEmployee-BasePlusCommissionEmployee Inheritance Hierarchy Using private Data
Reexamine hierarchy
Use the best software engineering practice
Declare data members as private
Provide public get and set functions
Use get method to obtain values of data members 42

43. CommissionEmployee.h相同
// Fig. 12.4: CommissionEmployee.h
#ifndef COMMISSION_H
#define COMMISSION_H
#include <string>
using namespace std;
class CommissionEmployee{
public:
CommissionEmployee(const string &, const string &, const string &, double = 0.0, double = 0.0);
void setFirstName(const string &);
string getFirstName() const;
void setLastName(const string &);
void setSocialSecurityNumber(const string &);
void setGrossSales(double);
double getFirstName() const;
void setCommissionRate(double);
double earnings() const;
void print() const;
private:
string firstName;
string lastName;
string socialSecurityNumber;
double grossSales;
double commissionRate; };
#endif
與12.4.1的
CommissionEmployee.h相同

44. 44
Outline
Commission Employee.cpp
(1 of 3)
Use member initializers to set the values of members firstName, lastname and socialSecurityNumber 44

45. 45
Outline
Commission Employee.cpp
(2 of 3) 45

46. 46
Outline
Commission Employee.cpp
(3 of 3)
Use get functions to obtain the values of data members 46

47. 12.5 Constructors and Destructors in Derived Classes
Instantiating derived-class object
Chain of constructor calls
Derived-class constructor invokes base class constructor
Implicitly or explicitly
Base of inheritance hierarchy
Last constructor called in chain
First constructor body to finish executing
Example: CommissionEmployee/BasePlusCommissionEmployee hierarchy
CommissionEmployee constructor called last
CommissionEmployee constructor body finishes execution first
Initializing data members
Each base-class constructor initializes its data members that are inherited by derived class 47

48. 12.5 Constructors and Destructors in 12.4.3~4
類別BasePlusCommissionEmployee
constructor的主體(使用域、scope) 48

49. 12.5 Constructors and Destructors in Derived Classes (Cont.)
Destroying derived-class object
Chain of destructor calls
Reverse order of constructor chain
Destructor of derived-class called first
Destructor of next base class up hierarchy next
Continue up hierarchy until final base reached
After final base-class destructor, object removed from memory
Base-class constructors, destructors, assignment operators
Not inherited by derived classes 49

50. 12.6 public, protected and private Inheritance50
12.6 public, protected and private Inheritance
public inheritance
Base class public members  derived class public members
Base class protected members  derived class protected members
Base class private members are not accessible
protected inheritance (not is-a relationship)
Base class public and protected members  derived class protected members
private inheritance (not is-a relationship)
Base class public and protected members  derived class private members 50

51. 51

52. Exercise 12.9 Package + 12 pairs set and get functions
senderName:string recipientName:string
senderAddress:string -recipientAddress:string
senderCity:string recipientCity:string
senderState:string recipientState:string
senderZip:int recipientZip:int
weight:double costPerOunce:double
+ 12 pairs set and get functions
+ calculateCost() : double
TwoDayPackage
OvernightPackage
- flatFee : double
- overnightFeePerOunce : double
+ setFlatFee(double)
+ getFlatFee(): double
+ calculateCost() : double
+ setOvernightFeePerOunce(double)
+ getOvernightFeePerOunce(): double
+ calculateCost(): double