lecture 02 programming... bs hons.. cs

7/26/2019 Lecture 02 Programming... Bs hons.. Cs

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Object Oriented

Programming

Using C++ Programming

Language


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RECAP

Object Orientation

A technique for system modeling

Model

A model is an abstractionof something Prototype/Architecture of a building

Purpose is to understand the product beforedeveloping it

Object

tate !attributes"

#ell$de%ned behavior !operations"

&nique identity


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'ecture ( )

*nformation +iding /

Encapsulation / Abstraction /Messages / Classes


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*nformation +iding

*nformation relevant to an object is

stored/pac,ed inside it- +idden/not accessible directly for

outside .orld-

Only object itself can manipulatedthe data/information under controlledenvironment-


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Eample 0 *nformation+iding +uman

Ahmad1s name is stored .ithin his

brain #e can1t access his name directly

Rather .e can as, him to tell his

name


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Eample 0 *nformation+iding

A phone stores several phone numbers

#e can1t read the numbers directlyfrom the *M card / phone memory-

Rather phone$set reads thisinformation for us2 3isplay in readableformat and manipulate safely


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Advantages of *nformation+iding

impli%es the model by hiding itsimplementation details2 hidescompleity of inside architecture-

Object its self handles data changes2*t restrict the change propagation


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Encapsulation

3ata and behavior related together arede%ned inside an object- 4hey aretightly coupled/dependent inside anobject

5oth the information structure andimplementation details of its operations

are hidden from the outer .orld


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Eample 0 Encapsulation

Ahmad stores his personalinformation and ,no.s ho. totranslate it to the desired language

#e don1t ,no.

+o. the data is stored

+o. Ahmad translates this information


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Eample 0 Encapsulation

A Phone stores phone numbers indigital format and ,no.s ho. toconvert it into human$readable

characters

#e don1t ,no.

+o. the data is stored

+o. it is converted to human$readablecharacters


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Encapsulation 0 Advantages

implicity and clarity

'o. compleity 5etter understanding

Avoid undesirable e6ects

ecurity


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Object has an *nterface

An object encapsulates data andbehaviour

o ho. objects interact .ith each other7

Each object provides an interface!operations"

Other objects communicate through thisinterface


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Eample 0 *nterface of a Car

teer #heels

Accelerate

Change 8ear Apply 5ra,es

4urn 'ights On/O6


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Eample 0 *nterface of aPhone

*nput 9umber

Place Call

3isconnect Call Add number to address boo,

end Message

&pdate number


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*mplementation

Provides services o6ered by theobject interface

4his includes

3ata structures to hold object state

:unctionality that provides requiredservices


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Eample 0 *mplementationof teering

3ata tructure

Mechanical structure of steering

:unctionality

Mechanism to rotate tyre


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Eample 0 *mplementationof Address 5oo, in a Phone

3ata tructure

*M card *nternal Memory

:unctionality Read/.rite circuitry


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eparation of *nterface ;*mplementation

Means change in implementationdoes not e6ect object interface

4his is achieved via principles of

information hiding and encapsulation


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Eample 0 eparation of*nterface ; *mplementation

A driver can drive a car independentof engine type !petrol2 diesel or C98"

5ecause interface does not change

.ith the implementation


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Advantages of eparation

&sers need not to .orry about achange until the interface is same

'o. Compleity !as implementationdetails are hidden"

3irect access to information

structure of an object can resulterrors/unstable state-


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Messages

Objects communicate throughmessages

4hey send messages !stimuli" byinvo,ing appropriate operations on thetarget object

4he number and ,ind of messages thatcan be sent to an object depends uponits interface


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Eamples 0 Messages

A Person sends message !stimulus"


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Abstraction

Abstraction is a .ay to cope .ithcompleity-

Principle of abstraction>


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Eample 0 Abstraction

Attributes$ 9ame $ Employee *3

$ tudent Roll 9o $ 3esignation

$ ?ear of tudy $ alary$ C8PA $ Age

Ahmad is a Ph3 student and teaches5 students


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4eacher1s Perspective


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Ahmad is a Ph3 student and teaches5 students

behaviour$ tudy $ 3evelopEam

$ 8iveEam $ 4a,eEam

$ Playports $ Eat$ 3eliver'ecture $ #al,


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tudent1s Perspective


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tudent1s Perspective


$ 8iveEam $ 4a,eEam



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4eacher1s Perspective


$ 8iveEam $ 4a,eEam



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Ordinary PerspectiveA pet animal .ith

:our 'egs

A 4ail

4.o Ears

harp 4eeth

urgeon1s PerspectiveA being .ith

A ,eleton

+eart @idney

tomach

A cat can be vie.ed .ith di6erentperspectives


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Owners View

Engineers View


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Abstraction 0 Advantages

impli%es the model by hidingirrelevant details

Abstraction provides the freedom to

defer implementation decisions byavoiding commitment to details


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Classes

*n an OO model2 some of the objectsehibit identical characteristics!information structure andbehaviour"

#e say that they belong to the sameclass


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Eample 0 Class

Ahmad studies mathematics

ara studies Computers cience

Mohsin studies chemistry

Each one is a tudent

#e say these objects are instancesofthe tudent class


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Eample 0 Class

Circle is an closed oval shape

quare is a closed rectangular shape

'ine is open shape .ith start andending point

Each one is a shape #e say these objects are instancesof

the shape class


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8raphical Representation ofClasses

!Class 9ame"

!attributes"

!operations"

!Class 9ame"

9ormal:orm

uppressed

:orm


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Eample 0 8raphicalRepresentation of Classes

Circle

centerradius

dra.computeArea

9ormal:orm

uppressed:orm

Circle


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Eample 0 8raphicalRepresentation of Classes

Student

name

agegender

tudy

8iveEams

9ormal:orm

uppressed:orm

Student


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; A

lecture 02 programming... bs hons.. cs

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