Inheritance

1
Inheritance

• Mechanism for deriving new classes from existing
  classes

2
Think of a Bicycle
3
Think of a Tandem Bike
4
Think of a Racing Bike
5
Think of a Mountain Bike
6
Thinking About Bicycles

• A tandem bicycle is a kind of bicycle
• Bicycle with two seats
• A mountain bicycle is a kind of bicycle
• Bicycle with shocks
• A racing bicycle is a kind of bicycle
• Lightweight aerodynamic construction
• Tandem, mountain, and racing bicycles are
  specialized bicycles

7
Wouldnt It Be Nice

• Be able to create specialized program objects
  without starting from scratch
• Use a previously defined object
• Specialize it as necessary
• Much less programming required
• Inheritance is the object-oriented programming
  mechanism for specialization

8
Inheritance

• Ability to define new classes of objects using
  existing classes as a basis

• Ability to define new classes of objects using
  existing classes as a basis
• The new class inherits the attributes and
  behaviors of the parent classes

• Ability to define new classes of objects using
  existing classes as a basis
• The new class inherits the attributes and
  behaviors of the parent classes
• New class is aspecialized versionof the parent
  class

9
Inheritance

• A natural way to reuse code
• Programming by extension rather than reinvention
• Object-oriented paradigm is well-suited for this
  style ofprogramming

• A natural way to reuse code
• Programming by extension rather than reinvention
• Object-oriented paradigm is well-suited for this
  style ofprogramming
• Terminology
• Base class (superclass)
• Derived class (subclass)

10
Class road_vehicle

• class road_vehicle
• int wheels
• int passengers
• public
• void set_wheels(int num) wheels num
• int get_wheels() return wheels
• void set_pass(int num)_passengers num
• int get_pass() return passengers

11
Class road_vehicle

• class road_vehicle
• int wheels
• int passengers
• public
• void set_wheels(int num) wheels num
• int get_wheels() return wheels
• void set_pass(int num)_passengers num
• int get_pass() return passengers
• //Use this definition to declare class truck
• class truck public road_vehicle
• int cargo
• public
• void set_cargo(int size) cargo size
• int get_cargo() return cargo
• void show()

12
Class road_vehicle

• class road_vehicle
• int wheels
• int passengers
• public
• ...
• // Base class road_vehicle, derived class
  truck
• class truck public road_vehicle
• int cargo
• public
• ...
• Truck inherits road_vehicle, so truck
  includes all of road_vehicle details and adds
  cargo to it

13
Class road_vehicle

• class road_vehicle
• int wheels
• int passengers
• public
• void set_wheels(int num) wheels num
• int get_wheels() return wheels
• void set_pass(int num)_passengers num
• int get_pass() return passengers
• // Truck inherits supporting member functions
• // And adds a few
• class truck public road_vehicle
• int cargo
• public
• void set_cargo(int size) cargo size
• int get_cargo() return cargo
• void show()

14
Inheritance - General Form

• class derived-class access base-class
• body of new class
• Example
• class truck public road_vehicle
• int cargo
• public
• void set_cargo(int size) cargo size
• int get_cargo() return cargo
• void show()
• access may be public, private, or protected
• For the time being use public in all cases
• All public members of the class will be public
  members of the derived class

15
Class road_vehicle

• class road_vehicle
• int wheels
• int passengers
• public
• void set_wheels(int num) wheels num
• int get_wheels() return wheels
• void set_pass(int num) passengers num
• int get_pass() return passengers
• //Use this definition to declare class
  automobile
• enum type car, van, wagon
• class automobile public road_vehicle
• type car_type
• public
• void set_type(type t) car_type t
• type get_type() return car_type
• void show()

16
road_vehicle Hierarchy
road_vehicle
automobile
truck
17
road_vehicle Hierarchy
private wheels passengers public
set_wheels() get_wheels() set_pass() get_pass()
road_vehicle
automobile
truck
private car_type public set_type()
get_type() show()
private cargo public set_cargo()
get_cargo() show()
18
Access Public

• When the base class is inherited as public, the
  public members of the base class are accessible
  to the derived class
• When the base class is inherited as private, the
  public members of the base class become private
  members of the derived class.
• class derived-class access base-class
• body of new class
• Example Inherits the public functions of
  road_vehicle
• class truck public road_vehicle
• int cargo
• public
• void set_cargo(int size) cargo size
• int get_cargo() return cargo
• void show()

19
Access Private

• When the base class is inherited as public, the
  public members of the base class are accessible
  to the derived class
• When the base class is inherited as private, the
  public members of the base class become private
  members of the derived class.
• Example Inherits the public functions of
  road_vehicle as private members
• class truck private road_vehicle
• int cargo
• public
• void set_cargo(int size) cargo size
• int get_cargo() return cargo
• void show()

20
Access Public
private wheels passengers public
set_wheels() get_wheels() set_pass() get_pass()
road_vehicle
automobile
truck
private car_type public set_type()
get_type() show()
private cargo public set_cargo()
get_cargo() show()
21
Access Private
private wheels passengers public
set_wheels() get_wheels() set_pass() get_pass()
road_vehicle
automobile
truck
private car_type public set_type()
get_type() show()
private cargo public set_cargo()
get_cargo() show()
22
Protected

• When a member of a class is declared as
  protected, that member is not accessible to
  other, non member elements of the program.
• Unlike a private member, it can be accessed by
  other members of the class of which it is part.
• Butwhen a protected member is inherited it
  differs from a private member
• IT CAN BE ACCESSED BY DERIVED CLASSES
• Example
• class road_vehicle
• protected
• int wheels // these are available to derived
• int passengers // classes
• public
• void set_wheels(int num) wheels num
• int get_wheels() return wheels
• void set_pass(int num) passengers num
• int get_pass() return passengers

23
Project 5

• //Base Class Definition
• class obj
• protected
• int id
• public
• obj() id 0 //Default Constructor
• obj(int num)id num
• void setid(int i) id i
• int getid() return id
• obj()

24
Project 5

• // Derived Class Definition
• class dobj public obj
• int a3
• public
• dobj() // Default Constructor sets //
  id 0, and a 0, 1, 2
• dobj(int num) // Constructor sets id num,
• // a 0, 1, 2
• void operator() // Increments id by one
• void operator--() // Decrements id by one
• int operator(int i) // Returns ai
• dobj()

25
Project 5

• void main()
• dobj a(14), b(15), c(16), d
• //cout
• cout
• cout
• cout
• cout
• for (int i 0 i
• a b c
• cout
• cout
• cout
• for (i 0 i