Computer Notes - Inheritance

8/3/2019 Computer Notes - Inheritance

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InheritanceInheritance

http://ecomputernotes.com


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RecapRecap InheritanceInheritance

Derived class inherits all the characteristics ofDerived class inherits all the characteristics of

the base classthe base class

Besides inherited characteristics, derived classBesides inherited characteristics, derived classmay have its own unique characteristicsmay have its own unique characteristics

Major benefit of inheritance is reuseMajor benefit of inheritance is reuse



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Concepts Related with InheritanceConcepts Related with Inheritance

GeneralizationGeneralization

SubtypingSubtyping (extension)(extension)

Specialization (restriction)Specialization (restriction)



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GeneralizationGeneralization

In OO models, some classes may have commonIn OO models, some classes may have common

characteristicscharacteristics

We extract these features into a new class andWe extract these features into a new class andinherit original classes from this new classinherit original classes from this new class

This concept is known as GeneralizationThis concept is known as Generalization



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ExampleExample GeneralizationGeneralization

Circlecolor

verticesradius

move

setColor

computeArea

Line

colorvertices

length

movesetColor

getLength

Trianglecolor

vertices

angle

move

setColor

computeArea



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ExampleExample GeneralizationGeneralizationShape

color

vertices

move

setColor

Circleradius

computeArea

Linelength

getLength

Triangleangle

computeArea



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ExampleExample GeneralizationGeneralization

Teachername

age

gender

designationsalary

teach

takeExam

eat

walk

Studentname

agegender

program

studyYear

studyheldExam

eat

walk

Doctorname

agegender

designation

salary

checkUpprescribe

eat

walkhttp://ecomputernotes.com


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ExampleExample GeneralizationGeneralizationPerson

name

agegendereat

walk

Teacherdesignation

salary

teach

takeExam

Studentprogram

studyYear

study

heldExam

Doctordesignation

salary

checkUp

prescribe


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SubSub--typing & Specializationtyping & SpecializationWe want to add a new class to an existingWe want to add a new class to an existing

modelmodel

Find an existing class that already implementsFind an existing class that already implementssome of the desired state andsome of the desired state and behaviourbehaviour

Inherit the new class from this class and addInherit the new class from this class and adduniqueunique behaviourbehaviour to the new classto the new class



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SubSub--typing (Extension)typing (Extension)

SubSub--typing means that derived class istyping means that derived class is

behaviourallybehaviourally compatible with the base classcompatible with the base class

BehaviourallyBehaviourally compatible means that base classcompatible means that base classcan be replaced by the derived classcan be replaced by the derived class



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ExampleExample

SubSub--typingtyping(Extension)(Extension)

Person

nameage

gender

eatswalks

Student

programstudyYear

study

takeExam


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ExampleExample

SubSub--typingtyping(Extension)(Extension)

Shapecolor

vertices

setColormove

Circle

radiuscomputeCF

computeArea


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Specialization (Restriction)Specialization (Restriction)

Specialization means that derived class isSpecialization means that derived class is

behaviourallybehaviourally incompatible with the base classincompatible with the base class

BehaviourallyBehaviourally incompatible means that baseincompatible means that baseclass canclass cant always be replaced by the derivedt always be replaced by the derived

classclass



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ExampleExample SpecializationSpecialization

(Restriction)(Restriction)Person

age : [0..100]

Adultage : [18..100]

setAge( a )

setAge( a )

age = a

If age < 18 thenerror

else

age = a


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ExampleExample SpecializationSpecialization

(Restriction)(Restriction)

IntegerSet

NaturalSet

add( elem )

add( elem )

add element

to the set

If elem < 1 then

errorelse

add element

to the set


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OverridingOverriding

A class may need to override the defaultA class may need to override the defaultbehaviourbehaviour provided by its base classprovided by its base class

Reasons for overridingReasons for overriding ProvideProvide behaviourbehaviour specific to a derived classspecific to a derived class

Extend the defaultExtend the default behaviourbehaviour Restrict the defaultRestrict the default behaviourbehaviour

Improve performanceImprove performance



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ExampleExample SpecificSpecific BehaviourBehaviourShape

color

verticesdraw

move

setColor

Circleradius

draw

computeArea

Linelength

draw

Triangleangle

draw

computeArea


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ExampleExample ExtensionExtensionWindow

width

height

open

close

draw

DialogBoxcontrolsenable

draw

1- Invoke Windowsdraw

2- draw the dialog

box


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ExampleExample RestrictionRestrictionIntegerSet

NaturalSet

add( elem )

add( elem )

Add element to

the set

If elem < 1 then

give error

elseAdd element to

the set



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ExampleExample Improve PerformanceImprove Performance

Class Circle overridesClass Circle overridesrotaterotate operation of classoperation of class

Shape with a NullShape with a Null

operation.operation.

Shapecolor

coorddraw

rotate

setColor

Circleradius

draw

rotate


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Abstract ClassesAbstract Classes

An abstract class implements an abstractAn abstract class implements an abstractconceptconcept

Main purpose is to be inherited by other classesMain purpose is to be inherited by other classesCanCant be instantiatedt be instantiated

Promotes reusePromotes reuse



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ExampleExampleAbstract ClassesAbstract Classes

TeacherDoctorStudent

Here, Person is an abstract classHere, Person is an abstract class

Personname

age

gender

eat

walk


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ExampleExampleAbstract ClassesAbstract Classes

Bus TruckCar

Here, Vehicle is an abstract classHere, Vehicle is an abstract class

Vehicle

colormodelaccelerate

applyBrakes


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Concrete ClassesConcrete ClassesA concrete class implements a concrete conceptA concrete class implements a concrete concept

Main purpose is to be instantiatedMain purpose is to be instantiated

Provides implementation details specific to theProvides implementation details specific to the

domain contextdomain context



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ExampleExample

Concrete ClassesConcrete Classes

Here, Student, Teacher and Doctor areHere, Student, Teacher and Doctor are

concrete classesconcrete classes

TeacherDoctorStudent

programstudyYear

study

heldExam

Person


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ExampleExample

Concrete ClassesConcrete Classes

Here, Car, Bus and Truck are concrete

classes

BusCar

Vehicle

Truckcapacityload

unload

Documents

Computer Notes - Inheritance