coen 244 - 3 - introduction to classes and object

7/23/2019 COEN 244 - 3 - Introduction to Classes and Object

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2008 Pearson Education, Inc. All rights reserved.

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3Introduction to

Classes andObjects


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3.1 Introduction

Programming languages may be classified intotwo categories,

.Procedural languages :Focus is on actions ( verbs), Ex: walking,

running. Ex. languages: C, Pascal.

.b!ect"#riented languages: Focus is on ob!ects (nouns), Ex: cars, $lanes,

elevators, %ouses. Ex. languages: C&&, 'ava.


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We live in a world of objects. Object-oriented design

(OOD) models software similar to tose tat !eo!le

describe te real-world objects. OOD !erformsinformation iding and software reuse.

- Objects ave attributes ( e.g. sa!e" color" si#e)

and beavior ( e.g. ball rolls" car runs" !lane flies).

- OOD enca!sulates attributes and o!erations

(beavior) into objects. - In C$$" te unit of !rogramming is class wile in C is

a function. Classes !erform information iding.

Classes ave two t%!es of members"

- Data members to store attributes - &unction members to store beavior

- Classes are used to create objects.

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'%!icall% rograms will consist of"

- &unction main

- One or more classes

ac class consists of two !arts*

1. Class definition*

- Define data members - rotot%!es of member functions

+. Class im!lementation

- It gives im!lementation of

member functions

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Class ,embers

ttributes Exist t%roug%out t%e life of t%e ob!ect

e$resented as data members

*ariables in a class definition

Eac% ob!ect of class maintains its own co$y of attributes

+ocal variables

*ariables declared in a function definitions body

Cannot be used outside of t%at function body -%en a function terminates

%e values of its local variables are lost


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Class ,ember ccess !ecifiers

ccess"s$ecifier: private

/akes a data member or member function accessible only

to member functions of t%e class

privateis t%e default access for class members

0ata %iding

ccess"s$ecifier: $ublic

data member or member function will be accessible also

to t%e clients of t%e class

eturning a value from a function function t%at s$ecifies a return ty$e ot%er t%an void

eturns a value to its calling function


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!

3./ lacing a Class in a e!arate &ile

for 0eusabilit%

Source code fle: Class implementation is stored in afle known as a source code fle and fle name has anextension .cpp.

1eader files

Class definitions are $laced in se$arate files known as

%eader files.

llow com$iler to recogni2e t%e classes w%en used elsew%ere

3enerally %ave .hfilename extensions

0river files

Program used to test software (suc% as classes)

Contains a mainfunction so it can be executed


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2008 Pearson Education,Inc. All rights reserved.

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"utline

fg03_11.cpp

(1 of 1)

1 / / i g. 3. 11: !r ade"ook. h

# / / !r ade"ook cl ass def ni t i on. $hi s f l e pr esent s !rade"ook% s pu&l i c

3 / / i nt er' ace wi t hout r eveal i ng t he i mpl ement ati ons o' !r ade"ook% smem&er

( / / ' unct i ons) whi ch are def ned i n !r ade"ook. cpp.

* +i ncl ude ,st r i ng- / / cl ass !r ade"ook uses C st andard str i ng cl ass

usi ng std: : str i ng

2 / / !r ade"ook cl ass def ni t i on

cl ass !r ade"ook

10 4

11 pu&l i c:

1# !r ade"ook5 st r i ng 6 / / const r uct or t hat i ni t i al i 7es cour se8ame

13 voi d setCour se8ame5 st r i ng 6 / / ' unct i on t hat sets t he cour se name

1( st r i ng getCour se8ame5 6 / / ' unct i on t hat gets t he cour se name1* voi d di spl a9essage5 6 / / ' unct i on t hat di spl a9s a wel come message

1 pr i vat e:

1 st r i ng cour se8ame / / cour se name ' or t hi s !r ade"ook

12 ; / / end cl ass !r ade"ook

Interface contains data members

and member function prototypes


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#

"utline

fg03_1#.cpp

(1 of 2)

Binary scope resolution operatorties a function to its class

GradeBookimplementation is

placed in a separate source-code file

Include the header file to access

the class name GradeBook


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"utline

fg03_1#.cpp

(2 of 2)


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"utline

fg03_13.cpp

(1 of 1)


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3. e!arating Interface from

Im!lementation (Cont.)

%e Com$ilation and +inking Process 4ource"code file is com$iled to create t%e classs ob!ect code

(source"code file must +include%eader file)

Class im$lementation $rogrammer only needs to $rovide%eader file and ob!ect code to client

Client must +include%eader file in t%eir own code

4o com$iler can ensure t%at t%e mainfunction creates andmani$ulates ob!ects of t%e class correctly

o create executable a$$lication

b!ect code for client code must be linked wit% t%e ob!ectcode for t%e class and t%e ob!ect code for any C&& 4tandard+ibrary ob!ect code used in t%e a$$lication

coen 244 - 3 - introduction to classes and object

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