1. Chapter 15 What is Inheritance?
Inheritance allows a new class to be based on an existing class.
The new class inherits all the member variables and functions of the class it is based on.
Note difference between is-a and has-a.
A station-wagon is-a car, but a car has-a wheel.

2. Inherited Class

3. Inheriting from Base Class

4. test.h - Program #ifndef TEST_H #define TEST_H #include "grade.h"
class Test : public Grade
{ private:
int numQuestions;
float pointsEach;
int numMissed;
public:
Test ( int, int );
}; // Test
#endif

5. Why would you want?
In our set example, we could derive sets with various differences
traits, prints differently
new methods, isKind
keep track of number of traits
Animals, add/replace features. Logical categorization
Cars, add common characteristics, options
Allows customization, reuse of base class.
Keeps design consistent. All cars have dealerRetail. All cars have taxAmount.

6. Protected Members and Class Access
Protected members of a base class are like private members, but they may be accessed by derived classes.
The base class access specification determines how private, protected, and public base class members may be accessed by derived classes.

7. Base Class Access

8. Constructors and Destructors
The base class’s constructor is called before the derived class’s constructor.
Since constructors have arguments, we are often not content with an argument-less call (the default).
The destructors are called in reverse order, with the derived class’s destructor being called first.

9. Passing Arguments to Base Class Constructors
Assume a class called Cube is derived from a class called Rect. Here is how the constructor looks in Rect:
Rect::Rect ( float w, float l )
{ width = w;
length = l;
area = length * width;
} // Rect::Rect

10. Cube Constructor Cube::Cube( float wide, float long, float high ) :
Rect(wide, long)
{ height = high;
volume = area * high;
} // Cube::Cube

11. Overriding Base Class Functions
A member function of a derived class may have the same name as a member function of a base class.

12. Polymorphism and Virtual Member Functions
The term polymorphism means the ability to take many form.
A virtual member function in a base class expects to be overridden in a derived class

13. Need for Virtual Member Functions

14. Abstract Base Classes and Pure Virtual Functions
An abstract base class is not instantiated, but other classes are derived from it.
A pure virtual function is a virtual member function of a base class that must be overridden.

15. Abstract Base Classes and Pure Virtual Functions (cont)
A class becomes an abstract base class when it contains one or more pure virtual functions.
A pure virtual function is a virtual member function declared in a manner similar to the following: virtual void showInfo(void) = 0;

16. Base Class Pointers
Pointers to a base class may be assigned the address of a derived class object.
The pointer, however, ignores any overrides the derived class performs

17. Classes Derived from Derived Classes
A base class can also be derived from another class.
This gives us a “chain” of inheritance where one class is derived from a second, which in turn is derived from a third.

18. Chain of Inheritance

19. Multiple Inheritance
Multiple inheritance is when a derived class has two or more base classes.

20. Multiple Inheritance (cont)

21. Examples
Could have a fruit which falls under two categories: both fruit and vegetable. A tomato is sometimes referred to as a fruit and sometimes as a vegetable.
fruit - the ripened reproductive body of a seed plant
vegetable - edible seeds or roots or stems or leaves or bulbs or tubers or nonsweet fruits of any of numerous herbaceous plant
Cross-categorization. An apple is a fruit and an apple is a breakfast food.

22. Given the following, organize them into inheritance or composition
A test for 1720, a student in 1720
An electronic device, a computer, a calculating tool
A woman, an employee, a person
A course, a course evaluation
Clothing, scarf, winter clothes, boots
Sesame Street Character, Big Bird, Oscar the Grouch

23. Concerns on multiple inheritance
Multiple inheritance is generally thought to be a bad idea because a common base class (B and C inherit from A, and D inherits from both B and C) cause problems with both B and C using the common variables differently.
Java handles with interface – function use is specified, but no implementation.