Computer Notes - Abstraction

8/3/2019 Computer Notes - Abstraction

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AbstractionAbstraction

http://ecomputernotes.com


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AbstractionAbstraction

Abstraction is a way to cope with complexity.Abstraction is a way to cope with complexity.

Principle of abstraction:Principle of abstraction:

Capture only those details about an object thatCapture only those details about an object thatare relevant to current perspectiveare relevant to current perspective



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ExampleExampleAbstractionAbstraction

AttributesAttributes

-- NameName -- Employee IDEmployee ID

-- Student Roll NoStudent Roll No -- DesignationDesignation

--Year of StudyYear of Study -- SalarySalary

-- CGPACGPA --AgeAge

Ali is a PhD student and teaches BS students



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ExampleExampleAbstractionAbstractionAli is a PhD student and teaches BS students

behaviourbehaviour

-- StudyStudy -- DevelopExamDevelopExam

-- GiveExamGiveExam -- TakeExamTakeExam

-- PlaySportsPlaySports -- EatEat

-- DeliverLectureDeliverLecture -- WalkWalk



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Students Perspective



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ExampleExampleAbstractionAbstractionStudents Perspective

behaviourbehaviour







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Teachers Perspective



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ExampleExampleAbstractionAbstractionTeachers Perspective

behaviourbehaviour







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Ordinary PerspectiveOrdinary Perspective

A pet animal withA pet animal with

Four LegsFour Legs

A TailA Tail Two EarsTwo Ears

Sharp TeethSharp Teeth

SurgeonSurgeons Perspectives Perspective

A being withA being with

A SkeletonA Skeleton

HeartHeart KidneyKidney

StomachStomach

A cat can be viewed with different perspectives



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Drivers View

Engineers View



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AbstractionAbstractionAdvantagesAdvantages

Simplifies the model by hiding irrelevant detailsSimplifies the model by hiding irrelevant details

Abstraction provides the freedom to deferAbstraction provides the freedom to deferimplementation decisions by avoidingimplementation decisions by avoiding

commitment to detailscommitment to details



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ClassesClasses

In an OO model, some of the objects exhibitIn an OO model, some of the objects exhibit

identical characteristics (information structureidentical characteristics (information structure

andand behaviourbehaviour))

We say that they belong to the same classWe say that they belong to the same class



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ExampleExample ClassClass

Ali studies mathematicsAli studies mathematics

AnamAnam studies physicsstudies physics

SohailSohail studies chemistrystudies chemistry

Each one is a StudentEach one is a Student

We say these objects areWe say these objects areinstancesinstances

of theof theStudent classStudent class



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ExampleExample ClassClass

AhsanAhsan teaches mathematicsteaches mathematics

AamirAamir teaches computer scienceteaches computer science

AtifAtifteaches physicsteaches physics

Each one is a teacherEach one is a teacher

We say these objects areWe say these objects areinstancesinstances

of theof theTeacher classTeacher class



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Graphical Representation of ClassesGraphical Representation of Classes

(Class Name)

(attributes)

(operations)

(Class Name)

Normal Form

Suppressed

Form



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ExampleExample Graphical Representation ofGraphical Representation of

ClassesClasses

Circle

center

radiusdraw

computeArea

Normal Form

Suppressed

Form

Circle



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ExampleExample Graphical Representation ofGraphical Representation of

ClassesClasses

Personname

age

gendereat

walk

Normal Form

SuppressedForm

Person



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InheritanceInheritance

A child inherits characteristics of its parentsA child inherits characteristics of its parents

Besides inherited characteristics, a child mayBesides inherited characteristics, a child mayhave its own unique characteristicshave its own unique characteristics



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Inheritance in ClassesInheritance in ClassesIf a class B inherits from class A then it containsIf a class B inherits from class A then it contains

all the characteristics (information structure andall the characteristics (information structure andbehaviourbehaviour) of class A) of class A

The parent class is calledThe parent class is called basebase

class and theclass and the

child class is calledchild class is called derivedderivedclassclass

Besides inherited characteristics, derived classBesides inherited characteristics, derived class

may have its own unique characteristicsmay have its own unique characteristics



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ExampleExample InheritanceInheritance

Person

TeacherDoctorStudent



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ExampleExample InheritanceInheritance

Shape

CircleTriangleLine



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InheritanceInheritanceIS AIS Aoror

IS A KIND OFIS A KIND OFRelationshipRelationship

Each derived class is a special kind of its baseEach derived class is a special kind of its baseclassclass



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ExampleExample

IS AIS A

RelationshipRelationship

Personname

agegendereat

walk

Teacherdesignationsalary

teach

takeExam

StudentprogramstudyYear

study

heldExam

Doctordesignationsalary

checkUp

prescribe


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ExampleExampleIS AIS ARelationshipRelationship

Shapecolor

coorddraw

rotate

setColor

Circleradius

draw

computeArea

Linelength

draw

Triangleangle

draw

computeArea


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InheritanceInheritanceAdvantagesAdvantages

ReuseReuse

Less redundancyLess redundancy

Increased maintainabilityIncreased maintainability



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Reuse with InheritanceReuse with InheritanceMain purpose of inheritance is reuseMain purpose of inheritance is reuse

We can easily add new classes by inheritingWe can easily add new classes by inheritingfrom existing classesfrom existing classes

Select an existing class closer to the desiredSelect an existing class closer to the desired

functionalityfunctionality

Create a new class and inherit it from the selectedCreate a new class and inherit it from the selected

classclass

Add to and/or modify the inherited functionalityAdd to and/or modify the inherited functionality



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Example ReuseExample ReuseShape

color

coorddraw

rotate

setColor

Circleradius

draw

computeArea

Linelength

draw

Triangleangle

draw

computeArea


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Example ReuseExample Reuse

Personname

agegendereat

walk

Teacher

designationsalary

teach

takeExam

Student

programstudyYear

study

heldExam

Doctor

designationsalary

checkUp

prescribe


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Example ReuseExample Reuse

Personname

agegendereat

walk

Teacher

designationsalary

teach

takeExam

Student

programstudyYear

study

heldExam

Doctor

designationsalary

checkUp

prescribe

Computer Notes - Abstraction

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