1. Today’s Objectives 5-Jul-2006 Announcements
Turn in HW #3 early for 10 bonus points on this HW
Homework #4 is posted, it is due on July 17
Quiz #3 will be on Monday, July 10 – Class string, string stream processing, operator overloading, and inheritance
Object-Oriented Programming: Inheritance (Ch. 12)
Reusability
Base classes and derived classes
“is-a” relationship
Using protected
Constructors and destructors
Other types of inheritance
Using typedef
Review of Homework #4
Library Demo (Continued)

2. Object-Oriented Programming: Inheritance
Chapter 12

3. Three Principle Features of Object-Oriented Programming
Object-Oriented Programming: Inheritance
Three Principle Features of Object-Oriented Programming
Encapsulation
Inheritance
Polymorphism

4. Reusability An important design goal of software engineering
Object-Oriented Programming: Inheritance (Deitel, 634–680, Goodrich)
Reusability
An important design goal of software engineering
Advantages
Saves time
Better to use code that is already tested

5. Object-Oriented Programming: Inheritance (Deitel, 634–680)
Allows reuse of code that is common between related classes
Create a base class that has the common code (also called a “parent” class)
Create a derived class that inherits from the base class (also called a “child” class)

6. UML Notation Base class Inheritance relationship Derived classes
Object-Oriented Programming: Inheritance (Deitel, 634–680)
UML Notation
Base class
Inheritance
relationship
Derived classes

7. “is-a” Relationship Represented by inheritance
Object-Oriented Programming: Inheritance (Deitel, 634–680)
“is-a” Relationship
Represented by inheritance
We say that an object of the derived class “is-a” object of the base class
Example:
“A Student is-a Person” is always true
However, an object of the base class is not an object of the derived class
Example – We cannot say, “A Person is-a Student,” because that is not always true

8. Examples Base class Derived class Person Student Account
Object-Oriented Programming: Inheritance
Examples
Base class
General
Code used by all derived classes
Derived class
Specific
Specialized code
Person
Student
Account
SavingsAccount
GamePlayer
Defender
Shape
Rectangle
RentalItem
Movie

9. Object-Oriented Programming: Inheritance (Deitel, 634–680)
Public Inheritance
One of three types of inheritance – the others are “private” and “protected”
Creates the “is-a” relationship
Most commonly used type of inheritance
class Student : public Person {
//... };
Derived class
Base class

10. Objects of the Derived Class
Object-Oriented Programming: Inheritance
Objects of the Derived Class
The derived class object automatically has all the data members and member functions that are in the base class
//Derived class objects can use base class functions
Student alice("Alice");
cout << alice.getName();
A derived-class object can be assigned to a base-class object
Student bob("Bob");
Person personBob = bob;
A derived-class object can be used as an argument when the function parameter is declared as a base-class object
void notify( Person& p ){ /*...*/ }
int main(){
notify(alice); }
Instantiate an object of the derived class
Use a base class member function
Assigning an object of the derived class
to a base class object
A function with a base class parameter
It can be called with a derived class object

11. Protected Members “protected” is a member-access specifier
Object-Oriented Programming: Inheritance (Deitel, 634–680)
Protected Members
“protected” is a member-access specifier
Protected members can be accessed by members and friends of both the base class and the derived classes
class Person{
protected:
string name;//Accessible in derived classes
public:
//... };

12. Single and Multiple Inheritance
Object-Oriented Programming: Inheritance (Deitel, 634, 1213)
Single and Multiple Inheritance
Single inheritance
When the derived class inherits from only one base class
Multiple inheritance
When the derived class inherits from more than one base class
Derived class has characteristics of both bases
Example:
class TA : public Student, Faculty{
//... };

13. Derived Class Initializer
Object-Oriented Programming: Inheritance (Deitel, 634–680)
Derived Class Initializer
Should explicitly call the base class constructor
Pass arguments to the base class constructor when appropriate
Example:
class Student : public Person{
public:
Student(string nm=""):Person(nm){}
//... };
Initializer list calls the constructor of the base class, and passes the argument to it
Constructor of the derived class

14. Overriding a Base Class Function
Object-Oriented Programming: Inheritance (Deitel, 634–680)
Overriding a Base Class Function
A derived class can redefine a function that it inherited from the base class
Example:
class Game : public RentalItem {
private:
string platform;
public:
string toString(){
return title + "Platform: " + platform; }
//... };
Redefinition of a member function of the base class

15. Calling a Base Class Function in the Derived Class
Object-Oriented Programming: Inheritance (Deitel, 634–680)
Calling a Base Class Function in the Derived Class
A base class function can be explicitly called from the derived class
Use the binary scope operator
class Game : public RentalItem {
private:
string platform;
public:
string toString(){
return RentalItem::toString()+"Platform: "+platform; }
//... };
Explicit call to a member function of the base class

16. Constructors and Destructors
Object-Oriented Programming: Inheritance (Deitel, 634–680)
Constructors and Destructors
Sequence of calls when an object of a derived class is instantiated
Base class constructor
Derived class constructor
Sequence of calls when an object of a derived class is destroyed
Derived class destructor
Base class destructor

17. Using typedef

18. Typedef Associates a name with a type
Using typedef (Deitel, 773)
Typedef
Associates a name with a type
Can be used to create a shorter or more meaningful name
Use the name like an alias
typedef Book* BookPtr;
BookPtr book1; //same as Book* book1
The alias

19. Library Demo
(Continued)

20. Library Demo Object-Oriented Programming: Inheritance
Since one of the requirements states that the library shall have both books and journals, we can create a base class called LibraryItem and two derived classes, Book and Journal
class Book : public LibraryItem {
//... };

21. Library Demo Object-Oriented Programming: Inheritance
A derived class can redefine a function that it inherited from the base class
class Journal : public LibraryItem {
public:
string toString(){
return LibraryItem::toString() + ", " + year; }
//...
Base class function
Redefines the
base class function

22. Library Demo Object-Oriented Programming: Inheritance
When a derived class object is assigned to a base class object, any members in the derived class that are not in the base class are lost
Journal journal("Dr. Dobbs","2004");
cout << journal.toString(); //prints "Dr. Dobbs, 2004"
LibraryItem item = journal;
cout << item.toString(); //prints "Dr. Dobbs"
prints "Dr. Dobbs"
prints
"Dr. Dobbs, 2004"

23. References
Deitel, H. M., and P. J. Deitel, C++ How to Program, Fourth Edition. Upper Saddle River, NJ: Prentice Hall, 2003.
Goodrich, M. T., R. Tamassia, and D. Mount, Data Structures and Algorithms in C++. Hoboken, NJ: John Wiley & Sons, Inc., 2004.