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Implementing Object-oriented Programming in

Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide " o# $%

Objectives

In t&is lesson' (ou )ill learn to*

Identi#( t&e ad+antages o# using classes and objects

Identi#( t&e use o# structures

Identi#( t&e use o# abstract classes in Visual Basic .NET

Identi#( t&e use o# inter#aces

Identi#( t&e di##erences bet)een inter#aces and abstract

classes

Identi#( t&e use o# assemblies

Identi#( t&e application &ierarc&( in Visual Basic .NET

,reate and instantiate a class

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Visual Basic .NET

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Objectives (Contd.)

eclare and import namespaces

,reate an in&erited #orm in Visual Basic .NET

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Visual Basic .NET


Object-orientation in Visual Basic .NETVisual Basic .NET*

!upports t&e #our pillars o# object-oriented programming*

Encapsulation bstraction

In&eritance

Pol(morp&ism 0ses prede#ined classes pro+ided b( t&e .NET

1rame)or2.

llo)s (ou to create (our o)n classes.

!upports structures t&at enable (ou to create (our o)ndata t(pe ata dapter.

lso &as #ull support #or inter#aces.

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Visual Basic .NET

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Classes and Objects

,lass

Is a conceptual representation o# all t&e entities t&at

s&are common attributes and be&a+iors.

e#ines t&e attributes and be&a+iors o# all t&e instances

o# t&e class.

Object Is an instance o# a class.

3as indi+idual cop( o# t&e common attributes and s&are

a common set o# be&a+iors.

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Visual Basic .NET

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Advantages of Using Classes and Objects

5aintenance o# code b( introducing modularit(.

Encapsulation o# internal comple6ities in code #rom

end-users.

7euse o# code across applications.

!upport #or a single inter#ace to implement multiple

met&ods.

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Visual Basic .NET


tructure

Is a generali9ation o# a user-de#ined data t(pe :0T;.

Is created )&en (ou )ant a single +ariable to &old multiple

t(pes o# related data.

Is declared b( using t&e Structure and End Structure

statements.

,an also include procedures as its members.

!upports e+ent &andling.

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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide < o# $%

tructure (Contd.)

=ou can speci#( t&e accessibilit( o# t&e data members )it&in

a structure b( using one o# t&e #ollo)ing access modi#iers*

Public

Protected

1riend

Protected 1riend

Pri+ate

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Visual Basic .NET

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tructure (Contd.)

!toring and accessing data )it&in/#rom a structure*

Is done b( using t&e .:dot; notation.

E6ample

Dim ord1 As order_details

ord1.Inv_no = "I0001“

ord1.Ord_dt = #5/31/2001#I ord1.Inv_no = "" !"en

s$%o&'()lease enter t"e Invoice num*er(+

End I

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Visual Basic .NET

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Classes Vs. tructure

#e) similarities bet)een a class and a structure are*

Bot& can &a+e members' including constructors'

properties' constants' and e+ents.

Bot& can implement inter#aces.

Bot& can &a+e s&ared constructors' )it& or )it&out

parameters.

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Visual Basic .NET

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Classes Vs. tructure (Contd.)

#e) dissimilarities bet)een a class and a structure are

gi+en in t&e #ollo)ing table*

Class Structure

A class is inheritable from other existing

classes.

A structure is not inheritable.

A class can have instance constructors

with or without parameters.

A structure can have instance

constructors only if they take parameters.

A class is a reference type. A structure is a value type.

The members of a class can be

initialized within the class declaration.

The members of a structure cannot be

initialized within the structure declaration.

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Visual Basic .NET

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Abstract Class

,ontains t&e s2eleton o# t&e met&ods t&at deri+ed

classes can implement.

E6ample

)u*lic ustIn"erit ,lass Em-loeeDetails

)u*lic ustOverride Su* Annual_Salar'%al m AsInte$er+

End ,lass

)u*lic ,lass Em-_details

In"erits Em-loeeDetails

)u*lic Overrides Su* Annual_Salar'%al m As Inte$er+ rite t"e im-lementation code "ere

End Su* End ,lass

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Visual Basic .NET


Abstract Class (Contd.)

=ou can create an abstract class b( using t&e

ustIn"erit 2e()ord in t&e class de#inition.

=ou can de#ine a met&od in an abstract class using t&eustOverride 2e()ord.

=ou must implement t&e met&od in deri+ed classes using

t&e Overrides 2e()ord.

I# a deri+ed class o# an abstract class does not implement

one o# t&e abstract met&ods o# t&e abstract base class' it

also must be declared )it& ustIn"erit 2e()ord as it

also becomes an abstract class.

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Visual Basic .NET


!nterface

,an contain onl( t&e declaration o# members suc& asproperties' met&ods' and e+ents.

Enables (ou to separate t&e de#inition o# objects #rom t&eirimplementation so t&at t&e objects can e+ol+e )it&out t&eris2 o# introducing incompatibilit( in e6isting applications.

Is declared b( using t&e Interace and End Interace statements.

E6ample

Interace Iorderdetails

)ro-ert ,ustame'+ As Strin$

Su* -date,ustStatus'+Event -date_,om-lete'+

End Interace

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Visual Basic .NET

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!nterface (Contd.)

!tatements are )u*lic b( de#ault.

,an in&erit members #rom an e6isting inter#ace b( using t&e

In"erits statement.

E6ample

Interace alidate_,ust

Su* alidate_,ustname'+

End InteraceInterace Iorderdetails In"erits

alidate_,ust

)ro-ert ,ustame'+ As Strin$

Su* -date,ustStatus'+Event -date_,om-lete'+

End Interace

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Visual Basic .NET

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"ifferences Bet#een !nterfaces and Abstract Classes

Inter#aces represent t&e &ig&est le+el o# abstraction in

object-oriented programming because all t&e met&ods in an

inter#ace do not &a+e an( implementation.

In contrast' t&e abstract classes t&at are created b( using

t&e ustIn"erit 2e()ord mig&t contain a met&od

t&at &as a bod(.

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Visual Basic .NET

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Asse$blies

,onsist o# a single or multiple e6ecutable and resource #iles

t&at contain in#ormation necessar( #or deplo(ing and

maintaining t&e +ersions o# an application.

Enable users to use an application e+en )&en t&e

application is not registered in t&e !(stem 7egistr(' since*

E+er( assembl( is sel#-describing t&roug& metadata.

E+er( re#erence to a t(pe is scoped b( an assembl(

re#erence.

.NET can automaticall( locate re#erenced assemblies.

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Visual Basic .NET

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Asse$blies (Contd.)

T&e application &ierarc&( in Visual Basic .NET is illustrated

in t&e #ollo)ing #igure*

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Visual Basic .NET

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Asse$blies (Contd.)

,onsist o# mani#est' module' and t(pe.

5ani#est is t&e descriptor o# t&e assembl(. It contains

in#ormation on*

T&e name and +ersion number o# t&e assembl(.

Its interaction )it& ot&er assemblies.

T&e t(pes e6posed b( t&e assembl(.

!ecurit( permissions re@uired b( t&e assembl(.

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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide "> o# $%

Asse$blies (Contd.)

5odule is eit&er a LL or EAE. It contains*

,ompiled code in intermediate languages.

5etadata associated )it& t&e module.

Optionall(' t&e mani#est #or t&e assembl(.

T(pe in Visual Basic .NET can be a class or a structure t&at

contain data and logic a##ecting t&e data.

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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide ? o# $%

%ust a &inute' . &( is a structure called a composite data t(peC

. Identi#( t&e s(ntactical error in t&e #ollo)ing declaration o#

an inter#ace*Interace I-roductdetails

)ro-ert )roductame'+ As Strin$

Su* -date,ustStatus'+

4a*el1.!e&t=!"is is a Su* )rocedure to c"ec6 t"e status o

t"e -roduct7

End Su*

Event -date_com-lete'+

End Interace

. 3o) are inter#aces di##erent #rom abstract classesC

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Visual Basic .NET


roble$ tate$ent .".*

T&e call centers at ia9 Telecommunications need to maintain

customer in#ormation to respond to customer @ueries. T&e

details o# t&e customers need to be accepted t&roug& a

grap&ical inter#ace. T&e customer in#ormation also needs to

be stored in t&e rele+ant memor( +ariables. T&e details o# t&e

customers essentiall( include customer id' customerDs #irst

name' customerDs last name' address' telep&one number' and

customerDs e-mail id.

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Visual Basic .NET


Tas+ ,istIdenti#( t&e data t&at needs to be captured.

Identi#( t&e t(pe o# user inter#ace to be used.

Identi#( t&e user inter#ace components to accept data.

Identi#( t&e mec&anism to store data in t&e rele+antmemor( +ariables.

Identi#( t&e memor( +ariables to store customerin#ormation.

Per#orm appropriate steps to create t&e user inter#acescreen' as designed.

dd a class to t&e project.rite t&e code to add t&e rele+ant members to a class.

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Visual Basic .NET


Tas+ ,ist (Contd.)

rite t&e code to instantiate t&e class.

rite t&e code to store and retrie+e data #rom t&e class.

!a+e t&e application.

7un t&e application.

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Visual Basic .NET


Tas+ * !dentif t/e data t/at needs to be ca0tured.

7esult

s per t&e problem statement' t&e data t&at needs to be

captured is* ,ustomer I

1irst Name

Last Name ddress

Telep&one number

E-mail I

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Visual Basic .NET


Tas+ 1 !dentif t/e t0e of user interface to be used.T&ere are t&ree t(pes o# user inter#aces*

indo)s 1orms

eb 1orms ,onsole

7esult*

!ince t&e re@uirement stated in t&e problem statement is #ora grap&ical user inter#ace' (ou )ill use indo)s 1orms

as t&e user inter#ace.

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Visual Basic .NET


Tas+ !dentif t/e user interface co$0onents toacce0t data.

uidelines #or designing a user inter#ace*

Identi#( t&e name and title o# t&e #orm.

Identi#( t&e controls re@uired.

7ecommend suitable pre#i6es t&at (ou can use #or

+arious controls*Object Prefix Example

Form frm frmCustomerdetail

s

Label lbl lblCustomerame

Text!ox txt txtCustomerame

!utton cmd cmd"ave

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Visual Basic .NET


Tas+ !dentif t/e user interface co$0onents toacce0t data. (Contd.)

7esult*

Based on t&e guidelines' set t&e #orm name as#rm,ustomerdetails and t&e te6t' )&ic& is t&e title o# t&e

#orm' as ,ustomer etails.

To ma2e a user-#riendl( inter#ace' add label controls to

displa( static te6t #or t&e customer details* ,ustomer I'1irst Name' Last Name' ddress' Telep&one number' and

Email I. Ne6t' add te6t bo6 controls to accept in#ormation

#or eac& customer detail. In addition' add t)o buttons

to sa+e and retrie+e t&e data stored #or t&e customer.

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Visual Basic .NET


Tas+ 2 !dentif t/e $ec/anis$ to store data inrelevant $e$or variables.

In Visual Basic .NET' (ou can store data in rele+ant

memor( +ariables b( implementing t&e object oriented‑

#eatures. T&e object-oriented #eatures enable (ou to create

a class t&at &as member +ariables to store data during

data processing.

7esult*!ince t&e re@uirement stated in t&e problem statement is to

store customer in#ormation in t&e rele+ant memor(

+ariables' a class called ,ustomer needs to be created

t&at )ill &a+e member +ariables to store customerin#ormation.

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Visual Basic .NET


Tas+ 3 !dentif t/e $e$or variables to storecusto$er infor$ation.

7esult*

!ince t&e customer in#ormation is to be stored in t&emember +ariables o# t&e ,ustomer class' (ou need to add

+ariables to t&e ,ustomer class. Eac& member

+ariable o# t&e ,ustomer class s&ould store a particular

t(pe o# customer detail. =ou must ensure t&at t&e data

t(pe o# a member +ariable matc&es t&e data t(pe o# t&e

customer detail stored b( t&e +ariables. !i6 member

+ariables need to be declared in t&e ,ustomer class.

O

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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide ? o# $%

Tas+ 4 erfor$ a00ro0riate ste0s to create t/e userinterface screen5 as designed.

Tas+ 6 Add a class to t/e 0roject.

Namespace

Is a naming sc&eme t&at &elps (ou organi9e t&e classesa+ailable in an application so t&at t&e( can be easil(#ound.

Enables (ou to a+oid name collisions. Is created using t&e Namespace 2e()ord.

E+er( project in Visual Basic .NET &as a rootnamespace' )&ic& is set in t&e Propert( page o# t&e

project. =ou can use namespaces e6plicitl( t&roug& direct

addressing or implicitl( t&roug& t&e Imports statement.

I l ti Obj t i t d P i i

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Visual Basic .NET


Tas+ 7 8rite t/e code to add t/e relevant $e$bersto a class.

Tas+ 9 8rite t/e code to instantiate t/e class.

Object Li#etime

T&e li#e o# an object begins )&en an instance o# a class

is created using t&e e8 2e()ord.

T&e li#e o# an object ends a#ter it goes out o# scope or isset to ot"in$ and is released b( t&e .NET

1rame)or2.

,onstructors

re o# t)o t(pes' s&ared constructors and instance

constructors.


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Visual Basic .NET


/ared Constructors0sed to initiali9e t&e +ariables t&at are declared )it& t&eS"ared 2e()ord.

3a+e an implicit )u*lic access.

ill not run more t&an once during a single e6ecution o# aprogram.

E6ample

)u*lic ,lass class1

S"ared & As Inte$er

S"ared Su* e8'+

& = 10

End Su*

End ,lass


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Visual Basic .NET


!nstance Constructors0sed to initiali9e +ariables t&at are declared )it& Dim')u*lic' )rivate' 9riend' )rotected' and )rotected 9riend 2e()ords.

llo) access to s&ared +ariables.

E6ample

)u*lic ,lass class1

Dim & As Inte$er

)u*lic Su* e8'+

& = 10

End Su*

End ,lass

Implementing Object oriented Programming in

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Visual Basic .NET


"estructors

re special met&ods t&at are used to release an instance o#

a class #rom memor(. T&ere are t)o t(pes o# destructors in

Visual Basic .NET*

9inali:e' +

Dis-ose' +


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Visual Basic .NET


:inali;e ( ) "estructor Is called #rom t&e class to )&ic& it belongs or #rom t&e

deri+ed classes.

Is called a#ter t&e last re#erence to an object is released#rom t&e memor(.

Is automaticall( in+o2ed b( t&e .NET 1rame)or2 to destro(

objects in t&e memor(.


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Visual Basic .NET


"is0ose ( ) "estructor Is called to release a resource' suc& as a database

connection' as soon as t&e object using suc& a resource is

no longer in use.

Is not called automaticall(' and (ou must e6plicitl( call it

#rom a client application.


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Visual Basic .NET


Tas+ *

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Visual Basic .NET


roble$ tate$ent .".1

T&e call centers at ia9 Telecommunications need data entr(

#orms to store in#ormation in t&e ,ustomers' Orders' Fuer(

3andling' Products' and Emplo(ees databases. E+er( data

entr( #orm s&ould &a+e a similar user inter#ace )it& t&e 7esetand E6it buttons. Incorporate t&e inter#ace #or t&e Order details

#orm.


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Visual Basic .NET


Tas+ ,ist Identi#( t&e mec&anism to pro+ide a similar user inter#ace.

Identi#( t&e user inter#ace components to accept data.

Identi#( t&e additional user inter#ace controls.

,reate t&e user inter#ace screen' as designed.

dd code #or t&e controls.

Per#orm t&e prere@uisite tas2 to implement t&e planned

mec&anism.

Implement t&e mec&anism' as planned.


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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $? o# $%

Tas+ ,ist (Contd.) dd t&e additional user inter#ace control' as planned.

Per#orm t&e tas2s to displa( a similar user inter#ace.

dd code #or t&e in&erited controls.

!a+e t&e application.

7un t&e application.


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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $" o# $%

Tas+ * !dentif t/e $ec/anis$ to 0rovide a si$ilaruser interface.

In Visual Basic .NET' (ou can create a base #orm in a

project and t&en create a #orm t&at in&erits #rom t&e base

#orm.

7esult*

!ince t&e re@uirement stated in t&e problem statement is to

create a similar user inter#ace #or all t&e data entr( #orms'(ou can create a base #orm t&at &as t&e 7eset and E6it

buttons on it. =ou can t&en in&erit all t&e data entr( #orms

#rom t&e base #orm.


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Visual Basic .NET


Tas+ 1 !dentif t/e user interface co$0onents toacce0t data.

7esult*

!ince all t&e data entr( #orms must &a+e t&e 7eset and E6it

buttons' (ou need to design t&e user inter#ace o# t&e

base #orm )it& t&ese t)o buttons. =ou also need to speci#(

t&e Te6t and Name properties o# t&e #orm and t&e buttons

on t&e #orm.


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p e e t g Object o e ted og a g

Visual Basic .NET


Tas+ !dentif t/e additional user interfacecontrols.

7esult*

!ince t&e data entr( #orms #or t&e ,ustomers' Orders'

Fuer( 3andling' Products' and Emplo(ees databases must

&a+e +arious controls to accept data #rom a user' (ou

need to identi#( additional controls t&at need to be included

in t&e deri+ed #orms. In t&e current scenario' (ou )ill onl(

create a base #orm )it& t)o buttons and in&erit t&e #ormOrderGdetails.


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p g j g g

Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $$ o# $%

Tas+ 2 Create t/e user interface screen5 asdesigned.

Tas+ 3 Add code for t/e controls.

Tas+ 4 erfor$ t/e 0rere>uisite tas+ to i$0le$entt/e 0lanned $ec/anis$.

Tas+ 6 !$0le$ent t/e $ec/anis$5 as 0lanned.

Tas+ 7 Add t/e additional user interface control5 as0lanned.


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p g j g g

Visual Basic .NET

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Tas+ 9 erfor$ t/e tas+s to dis0la a si$ilar userinterface.

Tas+ *

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p g j g g

Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $8 o# $%

roble$ tate$ent ..*T&e call centers o# ia9 Telecommunications need to &a+e

data entr( #orms to store in#ormation in t&e ,ustomers'

Orders' Fuer( 3andling' Product' and Emplo(ees databases.

E+er( data entr( #orm s&ould &a+e a similar user inter#ace )it&t&e dd' 5odi#(' elete' 7eset and E6it buttons. Incorporate

t&e inter#ace #or t&e Fuer( 3andling data entr( #orm.


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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $< o# $%

u$$arIn t&is lesson' (ou learned t&at*

Visual Basic .NET is an object-oriented programming

language. structure is used to create user-de#ined data t(pes.

ata can be stored in and retrie+ed #rom a structure.

bstract classes are used to de#ine t&e s2eleton o# t&emet&ods t&at t&e deri+ed class can implement.

Inter#aces are in&eritable in Visual Basic .NET.

,lasses can be added to a Visual Basic .NET project.


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Visual Basic .NET

©NIIT Implementing Object-oriented Programming in VB .NET/Lesson /!lide $% o# $%

u$$ar (Contd.) n assembl( contains in#ormation necessar( #or deplo(ing

and maintaining t&e +ersions o# an application.

n assembl( consists o# mani#est' module' and t(pe. n important ad+antage o# using a namespace is t&e

pre+ention o# a name collision.

,lasses can be in&erited in a Visual Basic .NET project.

19849091-vb-net-tutorial-3

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