[PPT] - Computer Science II for Majors Lecture 10 and 11 Inheritance Dr. PowerPoint Presentation

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CMSC202 Computer Science II for Majors

Lecture 10 and 11 –

Inheritance

Dr. Katherine Gibson

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Last Class We Covered

Professor Chang substitute taught
Allocation methods

– Static, automatic, dynamic – new and delete

Dynamically allocating arrays

– Constructors and destructors

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Any Questions from Last Time?

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Today’s Objectives

To review the exam results
To understand the relationships between objects
To begin learning about inheritance

–To cover what is being inherited –To understand how inheritance and access to member variables interact

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Exam 1 Results

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Code Reuse

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Code Reuse

Important to successful coding
Efficient

– No need to reinvent the wheel

Error free

– Code has been previously used/tested – (Not guaranteed, but more likely)

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Code Reuse Examples

What are some ways we reuse code?

– functions – classes

Any specific examples?

– calling Insert() and a modified Delete() for Move() – calling accessor functions inside a constructor

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Code Reuse Examples

What are some ways we reuse code?

–Functions –Classes –Inheritance – what we’ll be covering today

Any specific examples?

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Object Relationships

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Refresher on Objects

Objects are what we call an instance of a class
For example:

– Rectangle is a class – r1 is a variable of type Rectangle – r1 is a Rectangle object

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Object Relationships

There are two types of object relationships
is-a

– inheritance

has-a

– composition – aggregation both are forms

f association

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Inheritance Relationship

A Car is-a Vehicle

This is called inheritance
The Car class inherits from the Vehicle class
Vehicle is the general class, or the parent class
Car is the specialized class, or child class, that

inherits from Vehicle

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Inheritance Relationship Code

class Vehicle { public: // functions private: int m_numAxles; int m_numWheels; int m_maxSpeed; double m_weight; // etc } ;

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all Vehicles have axles, wheels, a max speed, and a weight

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Inheritance Relationship Code

class Car { } ;

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Inheritance Relationship Code

class Car: public Vehicle { } ;

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don’t forget the colon here! Car inherits from the Vehicle class

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Inheritance Relationship Code

class Car: public Vehicle { public: // functions private: int m_numSeats; double m_MPG; string m_color; string m_fuelType; // etc } ;

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all Cars have a number of seats, a MPG value, a color, and a fuel type

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Inheritance Relationship Code

class Car: public Vehicle { /etc/ }; class Plane: public Vehicle { /etc/ }; class SpaceShuttle: public Vehicle { /etc/ }; class BigRig: public Vehicle { /etc/ };

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Composition Relationship

A Car has-a Chassis

This is called composition
The Car class contains an object of type Chassis
A Chassis object is part of the Car class
A Chassis cannot “live” out of context of a Car

– If the Car is destroyed, the Chassis is also destroyed

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Composition Relationship Code

class Chassis { public: // functions private: string m_material; double m_weight; double m_maxLoad; // etc } ;

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all Chassis have a material, a weight, and a maxLoad they can hold

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Composition Relationship Code

class Chassis { public: // functions private: string m_material; double m_weight; double m_maxLoad; // etc } ;

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also, notice that there is no inheritance for the Chassis class

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Composition Relationship Code

class Car: public Vehicle { public: // functions private: // member variables, etc. // has-a (composition) Chassis m_chassis; } ;

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Aggregation Relationship

a Car has-a Driver

this is called aggregation

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Aggregation Relationship

A Car has-a Driver

This is called aggregation
The Car class is linked to an object of type Driver
Driver class is not directly related to the Car class
A Driver can live out of context of a Car
A Driver must be “contained” in the Car
bject via a pointer to a Driver object

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Aggregation Relationship Code

class Driver: public Person { public: // functions private: Date m_licenseExpire; string m_licenseType; // etc } ;

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Driver itself is a child class of Person

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Aggregation Relationship Code

class Driver: public Person { public: // functions private: Date m_licenseExpire; string m_licenseType; // etc } ;

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Driver inherits all of Person’s member variables (Date m_age, string m_name, etc.) so they aren’t included in the Driver child class

Driver itself is a child class of Person

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Aggregation Relationship Code

class Car: public Vehicle { public: // functions private: // member variables, etc. // has-a (aggregation) Person *m_driver; } ;

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Visualizing Object Relationships

On paper, draw a representation of how the

following objects relate to each other

Make sure the type of relationship is clear

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Engine
Driver
Person
Owner
Chassis
Car
Vehicle
BigRig
Rectangle
SpaceShuttle

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Inheritance

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Inheritance Access Specifiers

inheritance can be done via public, private, or

protected

we’re going to focus exclusively on public
you can also have multiple inheritance

– where a child class has more than one parent

we won’t be covering this

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Hierarchy Example

Vehicle

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Hierarchy Example

Vehicle etc. Car Plane BigRig

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Hierarchy Example

Vehicle SUV etc. Sedan Car Plane BigRig Jeep Van

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Hierarchy Example

Vehicle SUV etc. Sedan Car Plane BigRig Jeep Van

Specialization

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Hierarchy Vocabulary

more general class (e.g., Vehicle) can be called:

– parent class – base class – superclass

more specialized class (e.g., Car) can be called:

– child class – derived class – subclass

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Hierarchy Details

parent class contains all that is common among

its child classes (less specialized)

– Vehicle has a maximum speed, a weight, etc. because all vehicles have these

member variables and functions of the parent

class are inherited by all of its child classes

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Hierarchy Details

child classes can use, extend, or replace the

parent class behaviors

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Hierarchy Details

child classes can use, extend, or replace the

parent class behaviors

use

– the child class takes advantage of the parent class behaviors exactly as they are

like the mutators and accessors from the parent class

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Hierarchy Details

child classes can use, extend, or replace the

parent class behaviors

extend

– the child class creates entirely new behaviors

a RepaintCar() function for the Car child class
mutators/accessors for new member variables

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Hierarchy Details

child classes can use, extend, or replace the

parent class behaviors

replace

– child class overrides parent class’s behaviors

(we’ll cover this later today)

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Outline

Code Reuse
Object Relationships
Inheritance

– What is Inherited – Handling Access

Overriding
Homework and Project

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What is Inherited

Vehicle Class

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What is Inherited

Vehicle Class

public fxns&vars

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What is Inherited

Vehicle Class

public fxns&vars
protected fxns&vars

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What is Inherited

Vehicle Class

public fxns&vars
protected fxns&vars
private variables
private functions

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What is Inherited

Vehicle Class

public fxns&vars
protected fxns&vars
private variables
private functions
copy constructor
assignment operator
constructor
destructor

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What is Inherited

Car Class

public fxns&vars
protected fxns&vars
private variables
private functions
copy constructor
assignment operator
constructor
destructor

Vehicle Class

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What is Inherited

Car Class

public fxns&vars
protected fxns&vars
private variables
private functions
copy constructor
assignment operator
constructor
destructor

Vehicle Class

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child class

members (functions & variables)

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What is Inherited

Car Class

public fxns&vars
protected fxns&vars
private variables
private functions
copy constructor
assignment operator
constructor
destructor

Vehicle Class

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child class

members (functions & variables) ?

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What is Inherited

Car Class

public

fxns&vars

Vehicle Class

private functions
copy constructor
assignment operator
constructor
destructor

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protected fxns&vars
private variables
child class

members (functions & variables)

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What is Inherited

Car Class

child class

members (functions & variables)

public

fxns&vars

protected

fxns&vars

Vehicle Class

private functions
copy constructor
assignment operator
constructor
destructor

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private variables

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What is Inherited

Car Class

public

fxns&vars

protected

fxns&vars

private

variables

Vehicle Class

private functions
copy constructor
assignment operator
constructor
destructor

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child class

members (functions & variables)

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What is Inherited

Car Class

public

fxns&vars

protected

fxns&vars

private

variables

Vehicle Class

private functions
copy constructor
assignment operator
constructor
destructor

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child class

members (functions & variables)

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What is Inherited

Car Class

public

fxns&vars

protected

fxns&vars

private

variables

Vehicle Class

not (directly) accessible by Car objects

private functions
copy constructor
assignment operator
constructor
destructor

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child class

members (functions & variables)

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What is Inherited

Car Class

public

fxns&vars

protected

fxns&vars

private

variables

Vehicle Class

not (directly) accessible by Car objects

private functions
copy constructor
assignment operator
constructor
destructor

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child class

members (functions & variables)

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What is Inherited

Car Class

public

fxns&vars

protected

fxns&vars

private

variables

Vehicle Class

not (directly) accessible by Car objects

private functions
copy constructor
assignment operator
constructor
destructor

can access and invoke, but are not directly inherited

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child class

members (functions & variables)

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Outline

Code Reuse
Object Relationships
Inheritance

– What is Inherited – Handling Access

Overriding
Homework and Project

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Handling Access

Child class has access to parent class’s:

– public member variables/functions – protected member variables/functions – but not private member variables/functions

How should we set the access modifier for

parent member variables we want the child class to be able to access?

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Handling Access

Do not make these variables protected!

– Leave them private!

Instead, child class uses public or protected

functions when interacting with parent variables

– Reason we implement accessors and mutators

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Announcements

Project 2 is out – you should have started!

–It is due Thursday, March 10th

Nothing over Spring Break

–Enjoy your temporary freedom!

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CMSC202 Computer Science II for Majors

Lecture 10 and 11 –

Inheritance

Last Class We Covered

– Static, automatic, dynamic – new and delete

– Constructors and destructors

Any Questions from Last Time?

Today’s Objectives

–To cover what is being inherited –To understand how inheritance and access to member variables interact

Exam 1 Results

Code Reuse

Code Reuse

– No need to reinvent the wheel

– Code has been previously used/tested – (Not guaranteed, but more likely)

Code Reuse Examples

– functions – classes

– calling Insert() and a modified Delete() for Move() – calling accessor functions inside a constructor

Code Reuse Examples

–Functions –Classes –Inheritance – what we’ll be covering today

Object Relationships

Refresher on Objects

– Rectangle is a class – r1 is a variable of type Rectangle – r1 is a Rectangle object

Object Relationships

– inheritance

– composition – aggregation both are forms

Inheritance Relationship

A Car is-a Vehicle

inherits from Vehicle

Inheritance Relationship Code

class Vehicle { public: // functions private: int m_numAxles; int m_numWheels; int m_maxSpeed; double m_weight; // etc } ;

all Vehicles have axles, wheels, a max speed, and a weight

Inheritance Relationship Code

class Car { } ;

Inheritance Relationship Code

class Car: public Vehicle { } ;

don’t forget the colon here! Car inherits from the Vehicle class

Inheritance Relationship Code

class Car: public Vehicle { public: // functions private: int m_numSeats; double m_MPG; string m_color; string m_fuelType; // etc } ;

all Cars have a number of seats, a MPG value, a color, and a fuel type

Inheritance Relationship Code

class Car: public Vehicle { /*etc*/ }; class Plane: public Vehicle { /*etc*/ }; class SpaceShuttle: public Vehicle { /*etc*/ }; class BigRig: public Vehicle { /*etc*/ };

Composition Relationship

A Car has-a Chassis

– If the Car is destroyed, the Chassis is also destroyed

Composition Relationship Code

class Chassis { public: // functions private: string m_material; double m_weight; double m_maxLoad; // etc } ;

all Chassis have a material, a weight, and a maxLoad they can hold

Composition Relationship Code

class Chassis { public: // functions private: string m_material; double m_weight; double m_maxLoad; // etc } ;

also, notice that there is no inheritance for the Chassis class

Composition Relationship Code

class Car: public Vehicle { public: // functions private: // member variables, etc. // has-a (composition) Chassis m_chassis; } ;

Aggregation Relationship

a Car has-a Driver

Aggregation Relationship

A Car has-a Driver

Aggregation Relationship Code

class Driver: public Person { public: // functions private: Date m_licenseExpire; string m_licenseType; // etc } ;

Driver itself is a child class of Person

Aggregation Relationship Code

class Driver: public Person { public: // functions private: Date m_licenseExpire; string m_licenseType; // etc } ;

Driver inherits all of Person’s member variables (Date m_age, string m_name, etc.) so they aren’t included in the Driver child class

Driver itself is a child class of Person

Aggregation Relationship Code

class Car: public Vehicle { public: // functions private: // member variables, etc. // has-a (aggregation) Person *m_driver; } ;

Visualizing Object Relationships

following objects relate to each other

Inheritance

Inheritance Access Specifiers

protected

– where a child class has more than one parent

Hierarchy Example

Vehicle

Hierarchy Example

Vehicle etc. Car Plane BigRig

Hierarchy Example

Vehicle SUV etc. Sedan Car Plane BigRig Jeep Van

Hierarchy Example

Vehicle SUV etc. Sedan Car Plane BigRig Jeep Van

Specialization

class Car: public Vehicle { /etc/ }; class Plane: public Vehicle { /etc/ }; class SpaceShuttle: public Vehicle { /etc/ }; class BigRig: public Vehicle { /etc/ };