.Net Interview Questions all in One

5/28/2018 .Net Interview Questions all in One

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1.What is OOPS?

OOPS is abbreviated as Object Oriented Programming system in which programs are considered as

a collection of objects. Each object is nothing but an instance of a class.

2.Write basic concepts of OOPS?

Following are the concepts of OOPS and are as follows:.

1.Abstraction.2.Encapsulation.

3.nheritance.

4.Polymorphism.

3.What is a class?

A class is simply a representation of a type of object. t is the blueprint! plan! template that describe

the details of an object.

4.What is an object?

Object is termed as an instance of a class" and it has its own state" behavior and identity.

5.What is Encapsulation?

Encapsulation is an attribute of an object" and it contains all data which is hidden. #hat hidden data

can be restricted to the members of that class.

$evels are Public"Protected" Private" nternal and Protected nternal.

6.What is Polyorphis?

Polymorphism is nothing butassigning behavior or value in a subclass to something that was

already declared in the main class. Simply" polymorphism ta%es more than one form.

!.What is "nheritance?nheritance is a concept where one class shares the structure and behavior defined in another class.

finheritance applied on one class is called Single nheritance" and if it depends on multiple classes"

then it is called multiple nheritance.

#.What are anipulators?

&anipulators are the functions which can be used in conjunction with the insertion '(() and

e*traction '++) operators on an object. E*amples are endl and setw.

$.%efine a constructor?

,onstructor is a method used to initiali-e the state of an object" and it gets invo%ed at the time of

object creation. ules forconstructor are:.

,onstructor /ame should be same asclass name.

,onstructor must have no return type.

1&.%efine %estructor?

0estructor is a method which is automatically called when the object ismade ofscope or destroyed.

0estructor name is also same asclass name but with the tilde symbol before the name.

11.What is "nline function?

nline function is a techni1ue used by the compilers and instructs to insert complete body of the

function wherever that function is used in the program source code.

12.What is a'irtual function?

2irtual function is a member function ofclass and its functionality can be overridden in its derived


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class. #his function can be implemented by using a %eyword called virtual" and it can be given

during function declaration.

2irtual function can be achieved in ,33" and it can be achieved in , $anguageby using function

pointers or pointers to function.

13.What isfrien( function?

Friend function is a friend of a class that is allowed to access to Public" private or protected data inthat same class. f the function is defined outside the class cannot access such information.

Friend can be declared anywhere in the class declaration" and it cannot be affected by access control

%eywords li%e private" public or protected.

14.What is function o'erloa(in)?

Function overloading is defined as a normal function" but it has the ability to perform different

tas%s. t allowscreation of several methods with the same name which differ from each other by

type of input and output of the function.

E*ample

void add'int4 a" int4 b)5

void add'double4 a" double4 b)5void add'struct bob4 a" struct bob4 b)5

15.What is operator o'erloa(in)?

Operator overloading is a function where different operators are applied and depends on the

arguments. Operator"6"7 can be used to pass through the function " and it has their own precedence

to e*ecute.

E*ample:

class comple* 8

double real" imag5

public:

comple*'double r" double i) :

real'r)" imag'i) 89

comple* operator3'comple* a" comple* b)5

comple* operator7'comple* a" comple* b)5

comple*4 operator'comple* a" comple* b)5

9

a;.


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Arguments.

,all by 2alue > 2alue passed will get modified only inside the function " and it returns the

same value whatever it is passed it into the function.

,all by eference > 2alue passed will get modified in both inside and outside the functions

and it returns the same or different value.

2&.What is super +ey,or(?

Super %eyword is used to invo%e overridden method which overrides one of its superclass methods.

#his %eyword allows to access overridden methods and also to access hidden members of the

superclass.

t also forwards a call from a constructor to a constructor in the superclass.

21.What is etho( o'erri(in)?

&ethod overriding is a feature that allows sub class to provide implementation of a method that is

already defined in the main class. #his will overrides the implementation in the superclass by

providing the same method name" same parameter and same return type.

22.What is an interface?

An interface is a collection of abstract method. f the class implements an inheritance" and then

thereby inherits all the abstract methods of an interface.

23.What is e-ception han(lin)?

E*ception is an event that occurs during the e*ecution of a program. E*ceptions can be of any type

> un time e*ception" Error e*ceptions. #hose e*ceptions are handled properly through e*ception

handling mechanism li%e try" catch and throw %eywords.

24.What are to+ens?

#o%en is recogni-ed by a compiler and it cannot be bro%en down into component elements.

?eywords" identifiers" constants" string literals and operators are e*amples of to%ens.

Even punctuation characters are also considered as to%ens > @rac%ets" ,ommas" @races and

Parentheses.

25.%ifference bet,een o'erloa(in) an( o'erri(in)?

Overloading is static binding whereas Overriding is dynamic binding. Overloading is nothing but

the same method with different arguments " and it may or may not return the same value in the same

class itself.

Overriding is the same method names with same arguments and return types associates with the

class and its child class.

26.%ifference bet,een class an( an object?

An object is an instance of a class. Objects hold any information " but classes dont have any

information. 0efinition of properties and functions can be done at class and can be used by the

object.

,lass can have sub6classes" and an object doesnt have sub6objects.

2!.What is an abstraction?

Abstraction is a good feature of OOPS " and it shows only the necessary details to the client of an

object. &eans" it shows only necessary details for an object" not the inner details of an object.

E*ample > Bhen you want to switch On television" it not necessary to show all the functions of #2.Bhatever is re1uired to switch on #2 will be showed by using abstract class.


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2#.What are access o(ifiers?

Access modifiers determine the scope of the method or variables that can be accessed from other

various objects or classes. #here are C types of access modifiers " and they are as follows:.

Private.

Protected.

Public.Friend.

Protected Friend.

2$.What is seale( o(ifiers?

Sealed modifiers are the access modifiers where it cannot be inherited by the methods. Sealed

modifiers can also be applied to properties" events and methods. #his modifier cannot be applied to

static members.

3&.o, can ,e call the base etho( ,ithout creatin) an instance?

Des" it is possible to call the base method without creating an instance. And that method should be".

Static method.

0oing inheritance from that class.6se @ase ?eyword from derived class.

31.What is the (ifference bet,een ne, an( o'erri(e?

#he new modifier instructs the compiler to use the new implementation instead of the base class

function. Bhereas" Override modifier helps to override the base class function.

32.What are the 'arious types of constructors?

#here are three various types of constructors " and they are as follows:.

6 0efault ,onstructor > Bith no parameters.

6 Parametric ,onstructor > Bith Parameters. ,reate a new instance of a class and also passing

arguments simultaneously.6,opy ,onstructor > Bhich creates a new object as a copy of an e*isting object.

33.What is early an( late bin(in)?

Early binding refers to assignment of values to variables during design time whereas late binding

refers to assignment of values to variables during run time.

34.What is /this0 pointer?

#S pointer refers to the current object of a class. #S %eyword is used as a pointer which

differentiates between the current object with the global object. @asically" it refers to the current

object.

35.What is the (ifference bet,eenstructure an( a class?

Structure default access type is public " but class access type is private. A structure is used for

grouping data whereas class can be used for grouping data and methods. Structures are e*clusively

used for dataand it doesnt re1uire strict validation " but classes are used to encapsulates and inherit

data which re1uires strict validation.

36.What is the (efault access o(ifier in a class?

#he default access modifier of a class is Private by default.

3!.What is pure 'irtual function?

A pure virtual function is a function which can be overridden in the derived classbut cannot bedefined. A virtual function can be declared as Pure by using the operator G.

E*ample 6.


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2irtual void function;') !! 2irtual" /ot pure

2irtual void function


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bstraction

Abstraction refers to the act of representing essential features without including the bac%ground

details or e*planations.

Abstraction defines way to abstract or hide your data and members from outside world.

,lasses use the concept of abstraction and are defined as a list of abstract attributes.Simply spea%ing Abstraction is hiding the comple*ities of your class or struct or in a generic

term #ype from outer world.

#his is achieved by means of access specifiers.

ccess o(ifier %escription ,ho can access7

Private Only members within the same type. 'default for type members)

Protected Only derived types or members of the same type.

nternalOnly code within the same assembly. ,an also be code e*ternal to

object as long as it is in the same assembly. 'default for types)

Protected internalEither code from derived type or code in the same assembly.

,ombination of protected O internal.

PublicAny code. /o inheritance" e*ternal type" or e*ternal assembly

restrictions.

8o(e E-aple 9

namespace AbstractionE*ample

8

public abstract class Shape 8

private float Iarea5

private float Iperimeter5

public float Area 8 get 8 return Iarea5 9 set 8 Iarea value5 9 9

public float Perimeter 8 get 8 return Iperimeter5 9 set 8 Iperimeter value5 9 9

public abstract void ,alculateArea')5 public abstract void ,alculatePerimeter')5 9

9

Advantages of abstraction are

the hiding of implementation details" component reuse" e*tensibility" and testability. Bhen we hide

implementation details" we reveal a cleaner" more comprehensible and usable interface to our users.

Be are separating our interface from our implementation" and this ma%es component reuse more

practical. &any" if not all of the object6oriented concepts we have discussed throughout this

document play a role in the abstraction principle. Bor%ing together" their end goal is the same" toproduce software that is fle*ible" testable" maintainable" and e*tensible.

%efinition

Abstraction is one of the principle of object oriented programming. t is used to display only

necessary and essential features of an object to ouside the world.&eans displaying what is

necessary and encapsulate the unnecessary things to outside the world.iding can be achieved by

using JprivateJ access modifiers.

:ote 6 Outside the world means when we use reference of object then it will show only necessary

methods and properties and hide methods which are not necessary.

mplementation of Abstraction


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#o implement abstraction letKs ta%e an e*ample of a car. Be %nows a car" ,ar is made of name of

car" color of car" steering" gear" rear view mirror" bra%es" silencer" e*haust system" diesal engine" car

battery" car engine and other internal machine details etc.

/ow lets thin% in terms of ,ar rider or a person who is riding a car. So to drive a car what a car

rider should %now from above category before he starts a car driving.

/ecessary things means compulsary to %now before starting a car

;. /ame of ,ar


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public void Rear$ie%Mirror(

Console!rite#ine("Rear$ie%Mirror of Car"; }

public void &ra'es(

Console!rite#ine("&ra'es of Car"; } public void ear(

Console!rite#ine("ear of Car"; }

private void )nternal*etailsofCar(

Console!rite#ine(")nternal*etailsofCar of Car"; }

private void Car+ngine(

Console!rite#ine("Car+ngine of Car"; }

private void *iesal+ngine(

Console!rite#ine("*iesal+ngine of Car"; }

private void +,-austSystem(

Console!rite#ine("+,-austSystem of Car"; }

private void Silencer(

Console!rite#ine("Silencer of Car"; }

}


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Encapsulation

Encapsulation is way to hide data" properties and methods from outside the world or

outside of the class scope and e*posing only necessary thing.Encapsulation complements

Abstraction. Abstraction display only important features of a class and Encapsulation hides

unwanted data or private data from outside of a class.t hides the information within the object and

prevents from accidental corruption.

o, ,e can achie'e Encapsulation

Be can achieve Encapsulation by using JprivateJ access modifier as shown in below snippet of

code.

class Employee8

private void .ccount)nformation(/ Console!rite#ine("*isplaying .ccount *etails";}

}

Bhy to use Encapsulation

Encapsulation means protecting important data inside the class which we do not want to be e*posed

outside of the class.$ets consider e*ample of a #elevision'#2).

f you have seen important #2 machine" #2 connections and #2 color tube is hidden inside the #2

case which is not been e*posed for viewers li%e us and e*posed only neccessary things of a #2 li%e

#2 ,hannel %eys" #2 volume %eys" O/!OFF switch" ,able Switch and #2 remote control for

viewers to use it.#his means #2 machine" #2 connections and #2 color tube is an unwanted data

and not needed for viewers to see is been hidden from outside the world.So encapsulation means

hiding the important features of a class which is not been needed to be e*posed outside of a class

and e*posing only necessary things of a class.ere hidden part of a class acts li%e Encapsulation

and e*posed part of a class acts li%e Abstraction.

class cls0elevision/

private void 0$mac-ine(/ Console!rite#ine("Mac-ine of a 0elevision";

}

private void 0$colortube(/ Console!rite#ine("Color 0ube of a 0elevision"; }

public void 0$1eys(/ Console!rite#ine("1eys of a 0elevision"; }public void 0$Remote(/

Console!rite#ine("Remote of a 0elevision"; }

public void 0$Screen(/ Console!rite#ine("ide Screen of a 0elevision";}}


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#he following are the benefits of encapsulation:

Protection of data from accidental corruption

Specification of the accessibility of each of the members of a class to the code outside the class

Fle*ibility and e*tensibility of the code and reduction in comple*ity

$ower coupling between objects and hence improvement in code maintainability.

;echope(ia e-plainsEncapsulation

Encapsulation in , is implemented with different levels of access to object data that can be

specified using the following access modifiers:

Public: Access to all code in the program

Private: Access to only members of the same class

Protected: Access to members of same class and its derived classes

nternal: Access to current assembly

Protected nternal: Access to current assembly and types derived from containing class

Abstraction Encapsulation

Abstraction solves the problem in the designlevel.

Encapsulation solves the problem in the implementation level.

Abstraction is used for hiding the unwanted

data and giving only relevant data.

Encapsulation is hiding the code and data into a single unit to protect the

data from outer world.

Abstraction is set focus on the object instead ofhow it does it.

Encapsulation means hiding the internal details or mechanics of how anobject does something.

Abstraction is outer layout in terms of design.For E*ample: 6 Outer $oo% of a iPhone" li%e it

has a display screen.

Encapsulation is inner layout in terms of implementation.For E*ample: 6 nner mplementation detail of a iPhone" how 0isplay

Screen are connect with each other using circuits

Difference between Encapsulation and Abstraction in OOPS

Abstraction and Encapsulation are two important Object Oriented Programming (OOPS) concepts.

Encapsulation and Abstraction both are interrelated terms.

Real Life Difference Between Encapsulation and Abstraction

Encapsulate means to hide. Encapsulation is also called data hiding.You can think Encapsulation like a

capsule (medicine tablet) which hides medicine inside it. Encapsulation is wrapping, just hiding properties

and methods. Encapsulation is used or hide the code and data in a single unit to protect the data rom the

outside the world. !lass is the best e"ample o encapsulation.

Abstraction reers to showing onl# the necessar# details to the intended user. As the name suggests,

abstraction is the $abstract orm o an#thing$. %e use abstraction in programming languages to make

abstract class. Abstract class represents abstract &iew o methods and properties o class.

Implementation Difference Between Encapsulation and Abstraction

1. Abstraction is implemented using interace and abstract class while Encapsulation is implemented using


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pri&ate and protected access modiier.

2. OOPS makes use o encapsulation to enorce the integrit# o a t#pe (i.e. to make sure data is used in an

appropriate manner) b# pre&enting programmers rom accessing data in a non'intended manner. hrough

encapsulation, onl# a predetermined group o unctions can access the data. he collecti&e term or

datat#pes and operations (methods) bundled together with access restrictions (publicpri&ate, etc.) is a class.

. E!ample of Encapsulation

!lass Encapsulation

*

pri&ate int marks+

public int arks

*

get * return marks+ - set * marks &alue+-

--

". E!ample of Abstraction

abstract class Abstraction

*

public abstract &oid doAbstraction()+

-

public class Abstraction/mpl0 Abstraction

* public &oid doAbstraction()

*

/mplement it -

-


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bstract 8lass

An abstract class cannot be instantiated. #he purpose of an abstract class is to provide a common

definition of a base class that multiple derived classes can share. For e*ample" a class library may

define an abstract class that is used as a parameter to many of its functions" and re1uire

programmers using that library to provide their own implementation of the class by creating a

derived class.

Abstract classes may also define abstract methods. #his is accomplished by adding the

%eyword abstractbefore the return type of the method.

Abstract classes are one of the essential behaviors provided by ./E#. ,ommonly" you would li%e to

ma%e classes that only represent base classes" and dont want anyone to create objects of these class

types. Dou can ma%e use of abstract classes to implement such functionality in , using the

modifier KabstractK.

An abstract class means that" no object of this class can be instantiated" but can ma%e derivations of

this.

An abstract class can contain either abstract methods or non abstract methods. Abstract members donot have any implementation in the abstract class" but the same has to be provided in its derived

class.

abstractclassabsClass

{

publicabstractvoidabstractMethod();

}

Also" note that an abstract class does not mean that it should contain abstract members. Even we can have an

abstract class only with non abstract members. For e*ample:abstractclassabsClass

{

publicvoidNonAbstractMethod()

{

Console.WriteLine("NonAbstract Method");

}}

A sample program that explains abstract classes:

using!ste;

naespaceabstractaple

{

//Creating an Abstract Class abstractclassabsClass

{

//A Non abstract method publicintAdd#$oNubers(intNu%& intNu')

{

returnNu% Nu';

}

//An abstract method, to be //overridden in derived class


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publicabstractintMultipl!#$oNubers(intNu%& intNu');

}

//A Child Class of absClass classabserived*absClass

{ +#A#hread,

staticvoidMain(string+, args)

{

//You can create an //instance of the derived class

abserived calculate - ne$abserived(); intadded - calculate.Add#$oNubers(%&'); intultiplied - calculate.Multipl!#$oNubers(%&'); Console.WriteLine("Added * {}&

Multiplied * {%}"& added& ultiplied);

}

//using override keyword, //implementing the abstract method //MultiplyTwoNumbers publicoverrideintMultipl!#$oNubers(intNu%& intNu')

{

returnNu% / Nu';

} }}

n the above sample" you can see that the abstract class abs,lasscontains two

methods Add#wo/umbersand&ultiply#wo/umbers. Add#wo/umbersis a non6abstract methodwhich contains implementation and&ultiply#wo/umbersis an abstract method that does not

contain implementation.

#he class abs0erivedis derived from abs,lassand the &ultiply#wo/umbersis implemented

on abs0erived. Bithin the &ain" an instance 'calculate) of the abs0erivedis created" and

calls Add#wo/umbersand&ultiply#wo/umbers. Dou can derive an abstract class from another

abstract class. n that case" in the child class it is optional to ma%e the implementation of the abstract

methods of the parent class.

//Abstract Class1abstractclassabsClass%

{

publicabstractintAdd#$oNubers(intNu%& intNu'); publicabstractintMultipl!#$oNubers(intNu%& intNu');

}

//Abstract Class

abstractclassabsClass'*absClass%

{

//!mplementing AddTwoNumbers publicoverrideintAdd#$oNubers(intNu%& intNu')

{ returnNu%Nu';

}


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}

//"erived class from absClass

classabserived*absClass'

{

//!mplementing MultiplyTwoNumbers

publicoverrideintMultipl!#$oNubers(intNu%& intNu')

{

returnNu%/Nu';

}}

Inthe above e*ample" abs,lass; contains two abstract methods Add#wo/umbersand &ultiply#wo/umbers.#heAdd#wo/umbersis implemented in the derived class abs,lass


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abstractsealedclassabsClass

{

}

Declaration of abstract methods are only allowed in abstract classes.

An abstract method cannot be private.//!ncorrectprivateabstractintMultipl!#$oNubers();

The access modifier of the abstract method should be same in both the abstract class and its derived

class. If you declare an abstract method as protected, it should be protectedin its derived class.

therwise, the compiler will raise an error.

An abstract method cannot have the modifier virtual. !ecause an abstract method is implicitly virtual.//!ncorrect

publicabstractvirtualintMultipl!#$oNubers();

An abstract member cannot be static.//!ncorrectpublpublic abstractstaticintMultipl!#$oNubers();

Abstract class vs. nterface

An abstract class can have abstract members as well non abstract members. !ut in an interface all the

members are implicitly abstract and all the members of the interface must override to its derived class.

An example of interface:

inter0aceiaple1nter0ace

{

//All methods are automaticall abstract intAddNubers(intNu%& intNu'); intMultipl!Nubers(intNu%& intNu');

}

Defining an abstract class with abstract members has the same effect to defining an interface.

The members of the interface are public with no implementation. Abstract classes can have protected

parts, static methods, etc.

A class can inherit one or more interfaces, but only one abstract class.

Abstract classes can add more functionality without destroying the child classes that were using the oldversion. In an interface, creation of additional functions will have an effect on its child classes, due to the

necessary implementation of interface methods to classes.

The selection of interface or abstract class depends on the need and design of your pro"ect. #ou can

ma$e an abstract class, interface or combination of both depending on your needs.

bstract etho(

n an abstract class a method which has a %eyword JabstractJ and doesnKt provide any

implementation is called abstract method.#he implementation logic of abstract methods is provided

by the child classes or derived classes.,hild classes use %eyword JoverrideJ with same methodname 'as abstract method name) to provide further implementation of abstract methods.

:on bstract etho(

n an abstract class a method which doesnKt have a %eyword JabstractJ and provide any


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implementation is called non abstract method.

Why bstract 8lass

Abstract class enforces derived classes to provide all implementation logic for abstract methods or

properties.


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but the superclass itsel will ne&er e"ist. 1or e"ample, a class 2ersonwill ne&er e"ist. 2owe&er a

class Woanwill. /nstead o repeating all the methods that are in Woan, in Man, 3o!and 4irl, we

simpl# raise it to the superclass, so the# all ha&e access to this unctionalit#, and can o&erride the

methods that the# want to perorm dierentl#.

Interfaces

/nteraces are used when there is a re3uirement. he wa# / look at them is like a contract. he

agreement being that an# class that implements the /nterace, will ha&e to pro&ide code or a certain

number o methods.

1or e"ample, A class 5oc6and a class 3allcan both be thrown. /nstead o the method to throw a ball

ha&ing to take into account e&er# object that can be thrown, i e&er# object /mplements

the #hro$ing1te/nterace (/ didn4t want to use the word #hro$ableor ob&ious reasons), then the

method can just accept an object o t#pe #hro$ing1teand knows or a act that the agreed methods

will be there.

his enables loose coupling between the thro$method and the classes that use it, because all

communication is done through the interace.

f you have a type that can be designed as either an interface or an abstract class" why would you choose abstract

classQ

n that sense" we only use abstract class when some features cannot be done in interface:

;.state. though an interface could as% subclasses to implement state" it might be more convenient to use an

abstract super class to hold the state.

.:E; ,ith e-aple

Bhen you want to allow a derived class to override a method of the base class" within the base classmethod must be created as virtual method and within the derived class method must be created

using the %eyword override.

Bhen a method declared as virtual in base class" then that method can be defined in base class and

it is optionalfor the derived class to override that method.

Bhen it needs same definition as base class" then no need to override the method and if it needs

different definition than provided by base class then it must override the method.

&ethod overriding also provides more than one form for a method. ence it is also an e*ample for

polymorphism.

;he follo,in) e-aple creates three classes shape circle an( rectan)le ,here circle an(


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rectan)le are inherite( fro the class shape an( o'erri(es the etho(s rea7 an(

8ircuference7 that are (eclare( as 'irtual in Shape class.

usingSystem5namespaceProgram,all

8 classShape

8 pro tec te dfloat" $" @5

pub lic virtual float Area') 8

returnL.;MF 7 7 5 9

pub lic virtual float ,ircumference') 8

return< 7 L.;MF 7 5 9

9 classectangle: Shape

8

pub lic voidNet$@')

8 ,onsole.Brite'JEnter $ength : J)5

$ float.Parse',onsole .ead$ine'))5,onsole.Brite'JEnter @readth : J)5

@ float.Parse',onsole .ead$ine'))5 9

pub lic override floatArea') 8

return$ 7 @5 9

pub lic override float,ircumference')

8 return< 7 '$ 3 @)5 9

9 class,ircle: Shape

8 pub lic voidNetadius')

8

,onsole.Brite'JEnter adius : J)5

float.Parse',onsole .ead$ine'))5

9 9

class&ain,lass

8 staticvoid&ain')

8 ectangle ne wectangle ') 5

.Net$@')5 ,onsole.Brite$ine'JArea : 8G9J" .Area'))5

,onsole.Brite$ine'J,ircumference : 8G9J" .,ircumference'))5 ,onsole.Brite$ine')5

,ircle, new,ircle')5,.Netadius')5

,onsole.Brite$ine'JArea : 8G9J" ,.Area'))5

,onsole.Brite$ine'J,ircumference : 8G9J" ,.,ircumference'))5 ,onsole.ead')5 9

9


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9

A virtual method is a method that can be redefined in derived classes. A virtual

method has an implementation in a base class as well as derived the class. t is used

when a methodKs basic functionality is the same but sometimes more functionality is

needed in the derived class. A virtual method is created in the base class that can be

overriden in the derived class. Be create a virtual method in the base class using thevirtual %eyword and that method is overriden in the derived class using the override

%eyword.

Bhen a method is declared as a virtual method in a base class then that method can be

defined in a base class and it is optional for the derived class to override that method. #he

overriding method also provides more than one form for a method. ence it is also an e*ample for

polymorphism.

Bhen a method is declared as a virtual method in a base class and that method has the same

definition in a derived class then there is no need to override it in the derived class. @ut when a

virtual method has a different definition in the base class and the derived class then there is a need

to override it in the derived class.

Bhen a virtual method is invo%ed" the run6time type of the object is chec%ed for an overriding

member. #he overriding member in the most derived class is called" which might be the original

member" if no derived class has overridden the member.

Virtual Method

%.!y default, methods are non&virtual. 'e can(t override a non&virtual method.

).'e can(t use the virtual modifier with the static, abstract, private or override modifiers.

etho( O'erri(in) in 8>.:E;

,reating a method in derived class with same signature as a method in base class is called as

method overriding.Same signature means methods must have same name, same number ofarguments and same type of arguments.Method overriding is possible only in derived classes, but not within the same

class.

When derived class needs a method with same signature as in base class, butwants to execute different code than provided by base class then method

overriding will be used.

To allow the derived class to override a method of the base class, C# provides twooptions,virtual methods and abstract methods.

xamples for Method !verriding in C#usingSystem5

namespace methodoverriding8

class@ase,lass 8

pub lic virtual string Dour,ity') 8

returnJ/ew Dor%J5 9

9 class0erived,lass : @ase,lass


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8 pub lic override stringDour,ity')

8 returnJ$ondonJ 5

9 9

classProgram

8 staticvoid&ain'stringTU args) 8

0erived,lass obj new0erived,lass ') 5 stringcity ob j.Dour,ity')5

,onsole.Brite$ine'city)5

,onsole.ead')5

9 9

9

Output

$ondon

E*ample 6 < implementing abstract method

usingSystem5

namespace methodoverridinge*ample

8 abstract class@ase,lass

8 pub lic abstract stringDour,ity')5

9

class0erived,lass : @ase,lass 8

pub lic override stringDour,ity') !!t is mandatory to implement absract method 8

returnJ$ondonJ 5

9

pri va teint sum'int a" in tb )

8 returna 3 b5

9 9

classProgram 8

staticvoid&ain'stringTU args) 8 0erived,lass obj new0erived,lass ') 5

stringcity ob j.Dour,ity')5 ,onsole.Brite$ine'city)5

,onsole.ead')5 9

99

Output$ondon


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"nterface

An interface loo%s li%e a class but has got no implementation. n an interface we cannot do any

implementation but we can declare signatures of properties" methods" delegates and events.

mplementation part is been handle by the class that implements the interface. mplemented

interface enforces the class li%e a standard contract to provide all implementation of interface

members.

Be can implement single interface or multiple interfaces to the class. @y default interfaces are

public.

Be declare interface by using JinterfaceJ %eyword.

interface )+mployee/

void *isplay+mployee*etails(;

}

Above synta* shows simple demonstration of interface JEmployeeJ with signature of a method

J0isplayEmployee0etailsJ. /ow letKs implement the same interface to a class.

class clsEmployee : Employee/ public void *isplay+mployee*etails(/ Console!rite#ine(2*isplaying employee details34; }}

enefits of usin) an interface

mplemented interface enforces the class li%e a standard contract to provide all implementation of

interface members.

n architecting the project we can define the proper naming conventions of methods" properties in

an interface so that while implementing in a class we use the name conventions.

Be can use the JinterfaceJ as a pointer in the different layers of applications.Be can use an interface

for implementing run time polymorphism.

=arious @ors of ipleentin) interface

#here are two of ways of implementing interfaces

E*plicit

mplicit

E-plicit interface ipleentation

#o implement an interface e*plicitly we have to define an interface name followed by 'J.J) dot

operator then the method name.

public class Employee : Employee/ void )+mployee!*isplay+mployee*etails( / Console!rite#ine(")+mployee +mployee Name 556!!!!!"; }


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}

"n ,hich scenario ,e use e-plicit interface ipleentation

Bhen we have two different interfaces with same method name then in that scenario we can use

e*plicit interface implementation.

E*ample of E*plicit nterface

public interface Employee8 void *isplay+mployee*etails(;}

public interface )Company/ void *isplay+mployee*etails(;}

n order to implement an interface e*plicitly we have to define the interface name followed by ' A.A)

dot operator before method name as shown in below snipped code.

public class Employee : Employee",ompany

8 void ,ompany.0isplayEmployee0etails')8 ,onsole.Brite$ine'J,ompany Employee /ame 66+ Vuestpond and Employee ,ode 66+ GGWJ)5

9 void Employee.0isplayEmployee0etails')8

,onsole.Brite$ine'JEmployee Employee /ame 66+ Vuestpond and Employee ,ode 66+ GGWJ)5 9

9

Properties Of "nterface9B

Supports multiple inheritance'Single ,lass can implement multiple interfaces).

,ontains only incomplete method.

,an not ,ontains data members.

@y 0efault interface members is public 'Be ,an not set any access modifier into interface

members).

nterface can not contain constructors.

hide implementation details of classes from each other

facilitate reuse of software

"nterface characteristics in the Cco(e ,orl(D An iterface defines only the properties and method signatures and not the actual

implementation. mean that in a class declaration we implement fields"properties"methods

and events. n an interface we just define what properties!methods the class should have.

e1uires that classes which implement an interface must XhonourX the property and method

signatures. @asically are li%e contracts for classes. ,lasses which implement an interface

must implement the methods and the properties of the interface.

&any classes can implement a particular interface method" in their own way.

An interface may inherit from multiple base interfaces.

A class may implement6inherit from multiple interfaces.

A , class may only inherit from one class.


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Feature nterface Abstract class

&ultiple inheritance A class may inherit several

interfaces.

A class may inherit only

one abstract class.

0efault implementation An interface cannot

provide any code" just thesignature.

An abstract class can

provide complete" defaultcode and!or just the details

that have to be overridden.

Access &odfiers An interface cannot have

access modifiers for the

subs" functions" properties

etc everything is assumed

as public

An abstract class can

contain access modifiers

for the subs" functions"

properties

,ore 2S Peripheral nterfaces are used to

define the peripheralabilities of a class. n other

words both uman and

2ehicle can inherit from a

&ovable interface.

An abstract class defines

the core identity of a classand there it is used for

objects of the same type.

omogeneity f various implementations

only share method

signatures then it is better

to use nterfaces.

f various implementations

are of the same %ind and

use common behaviour or

status then abstract class is

better to use.

Speed e1uires more time to find

the actual method in the

corresponding classes.

Fast

Adding functionality

'2ersioning)

f we add a new method to

an nterface then we have

to trac% down all the

implementations of the

interface and define

implementation for the

new method.

f we add a new method to

an abstract class then we

have the option of

providing default

implementation and

therefore all the e*isting

code might wor% properly.

Fields and ,onstants /o fields can be defined in

interfaces

An abstract class can have

fields and constrants

defined


24/110

Polyorphis in 8>.:E;

According to &S0/" #hrough inheritance" a class can be used as more than one type5 it can be

used as its own type" any base types" or any interface type if it implements interfaces. #his is

called polymorphism.

n ," every type is polymorphic. #ypes can be used as their own type or as a Object instance"because any type automatically treats Object as a base type.

Polymorphism means having more than one form. Overloading and overriding are used to

implement polymorphism. Polymorphism is classified into compile time polymorphism or

early binding or static binding and untime polymorphism or late binding or dynamic binding

P o l y m o r p h i s m E * a m p l e s

etho( O'erloa(in)

etho( O'erri( in)

,ompile time Polymorphism or Early @inding

#he polymorphism in which compiler identifies w hich polymorphic form it has to

e*ecute at compile time it self is called as compile time polymorphism or early

binding .

Advantage of early binding is e*ecution will be fast. @ecause every thing about the

method is %nown to compiler during compilation it self and disadvantage is lac% of

fle*ibility.

E*amples of early binding are overloaded methods" overloaded operators and

overridden methods that are called directly by using derived objects.

untime Polymorphism or $ate @inding

#he polymorphism in which compiler identifies w hich polymorphic form to e*ecute at

runtime but not at compile time is called as runtime polymorphism or late binding.

Advantage of late binding is fle*ibility and disadvantage is e*ecution will be slow as

compiler has to get the information about the method to e*ecute at runtime.

E*ample of late binding is overridden methods that are called using base class object.
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Static 8lass

Astaticclass is basically the same as a non6static class" but there is one difference: a static class

cannot be instantiated. n other words" you cannot use the new%eyword to create a variable of the

class type. @ecause there is no instance variable" you access the members of a static class by using

the class name itself. For e*ample" if you have a static class that is named tility,lassthat has a

public method named &ethodA" you call the method as shown in the following e*ample:tility,lass.&ethodA')5

A static class can be used as a convenient container for sets of methods that just operate on input

parameters and do not have to get or set any internal instance fields. For e*ample" in the ./E#

Framewor% ,lass $ibrary" the staticSystem.&athclass contains methods that perform mathematical

operations" without any re1uirement to store or retrieve data that is uni1ue to a particular instance of

the&athclass. #hat is" you apply the members of the class by specifying the class name and the

method name" as shown in the following e*ample.

double dub 6L.;M5

Console.WriteLine(Math.Abs(dub));

Console.WriteLine(Math.7loor(dub));

Console.WriteLine(Math.5ound(Math.Abs(dub)));

88 9utput*

88 :.%

88


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public static class #emperature,onverter

{

public static double Celsius#o7ahrenheit(string teperatureCelsius)

{

88 Convert arguent to double 0or calculations.

double celsius - ouble.2arse(teperatureCelsius);

88 Convert Celsius to 7ahrenheit.

double 0ahrenheit - (celsius / = 8 >) :';

return 0ahrenheit;

}

public static double 7ahrenheit#oCelsius(string teperature7ahrenheit)

{

88 Convert arguent to double 0or calculations.

double 0ahrenheit - ouble.2arse(teperature7ahrenheit);

88 Convert 7ahrenheit to Celsius.

double celsius - (0ahrenheit < :') / > 8 =;

return celsius;

}

}

class #est#eperatureConverter

{

static void Main()

{

Console.WriteLine("2lease select the convertor direction");

Console.WriteLine("%. 7ro Celsius to 7ahrenheit.");

Console.WriteLine("'. 7ro 7ahrenheit to Celsius.");

Console.Write("*"); string selection - Console.5eadLine();

double 7& C - ;

s$itch (selection)

{

case "%"*

Console.Write("2lease enter the Celsius teperature* ");

7 - #eperatureConverter.Celsius#o7ahrenheit(Console.5eadLine());

Console.WriteLine("#eperature in 7ahrenheit* {*7'}"& 7);

brea6;

case "'"* Console.Write("2lease enter the 7ahrenheit teperature* ");

C - #eperatureConverter.7ahrenheit#oCelsius(Console.5eadLine());

Console.WriteLine("#eperature in Celsius* {*7'}"& C);

brea6;

de0ault*

Console.WriteLine("2lease select a convertor.");

brea6;

}

88 ?eep the console $indo$ open in debug ode.

Console.WriteLine("2ress an! 6e! to e@it."); Console.5ead?e!();

}

}


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Static you can use the method of the class which is static, but you ma"e sure that the valuegets changed as you reuired.

$f you are using the class and ob%ect concept it means that you are using the !!&S concepts.

Static class is used when you are aware of that the value that you are going to use in entireapplication will remain same means that at one place you will set the value and from other

place you will get that value, at that point of time it's better to use static class.

The following are rules to create a static class:

Rule#1. a static class must contain the static $eyword in the class declaration.ule>2. a method should be static i.e. the method declaration must contain the static %eyword.

ule>3. the ,onstructor must be static because a static class doesnKt allow an instance constructor.

ule>4. the ,onstructor must not contain an access modifier.

ule>5. a Static class canKt implement an inteface.

ule>6. a Static class canKt be a base class i.e. it cannot be derived from.

s a class whose members must be accessed without an instance of the class. n other words"

the members of a static class must be accessed directly from 'using the name of) the class"

using the period operator

1s a class $hose ebers ust be created as static. 1n other $ords&

!ou cannot add a non;

}
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}

public static void rive() { }

public static event Bvent#!pe 5un9ut904as;

88 9ther non


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class &ath

8

//Do something

public static double S1rt'double d)

8

//Do something

9

9

From the previous e*ample" you can notify that the S1rt method is declared as static so that it can be

accessed by using the class name directly" no object of the &ath class is re1uired to access

the static method.

So" here will li%e to some general properties of a static method:

t can access only the static fields of the class.

t can directly invo%e the methods that are defined as static.

Static @iel(s

A static field is shared among all the objects of the of the class. So if an object changes this value"

then all the objects of this class will get the changed value.

class Point

8

public Point')

8

this.* 6;5

this.y 6;5

,onsole.Brite$ine'J0eafult ,onstructor ,alledJ)5

object,ount335

9

public Point'int *" int y)

8

this.* *5

this.y y5

,onsole.Brite$ine'J* 8G9 " y 8;9J" *" y)5

object,ount335

9

private int *" y5

public static int object,ount G5

9

/ow if we create three objects for this class:

Point origin; new Point')5 //objectCount = 1

Point origin< new Point')5 //objectCount = 2


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Point originL new Point')5 //objectCount = 3

ere these three objects share the same field so every time the static field object,ount is

incremented.

Static 8lass

A static class is used to hold all the utility methods and fields. A static ,lass has some properties:

All the methods and fields inside the class must be declared as static.

A static class cannot contain any instance method or data./o object can be created 'even using the newX %eyword) of this class.

t can have a default constructor and it is also static.

E-aple

$et us consider an e*ample.

Point.cs

using System5

using System.,ollections.Neneric5using System.#e*t5

namespace ,onApp,Y,,ons

8

class Point

8

public Point')

8

this.* 6;5 this.y 6;5

,onsole.Brite$ine'J0eafult ,onstructor ,alledJ)5

object,ount335

9

public Point'int *" int y)

8

this.* *5

this.y y5

,onsole.Brite$ine'J* 8G9 " y 8;9J" *" y)5 object,ount335

9

public double 0istance#o'Point other)

8

int *0iff this.* 6 other.*5

int y0iff this.y 6 other.y5

return &ath.S1rt''*0iff 7 *0iff) 3 'y0iff 7 y0iff))5

9

public static int FnObject,ount')


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8

return object,ount5

9

private int *" y5 private static int object,ount G5

9

9

8onstructorE-aple.cs

using System5

using System.,ollections.Neneric5

using System.#e*t5

namespace ,onApp,Y,,ons

8

class ,onstructorE*ample

8

static void &ain'stringTU args)

8

Point origin new Point')5

Point bottomight new Point';G


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As it is a static method" it can hold only a static field or static method.

"nternal @unction

#he internal access specifier hides its member variables and methods from other

classes and objects" that is resides in other namespace. #he variable or classes that are

declared with internalcan be access by any member within application. t is thedefault access specifiers for a class in , programming.

usingSystem;

namespace)nternal_.ccess_Specifier/

classaccess

/

77 String $ariable declared as internal

internalstringname;

publicvoidprint(

/

Console!rite#ine("8nMy name is "9 name; }

}

class:rogram

/

staticvoidMain(string< args

/

accessac = ne%access(;

Console!rite("+nter your name8t";

77 .ccepting value in internal variable

ac!name = Console!Read#ine(;

ac!print(;

Console!Read#ine(;

}

}}

#he internal%eyword is an access modifier for types and type members. nternal types or members

are accessible only within files in the same assembly" as in this e*ample:

public class 3aseClass

{

88 9nl! accessible $ithin the sae assebl!

internal static int @ - ;}

#ypes or members that have access modifier protecte( internalcan be accessed from the current

assembly or from types that are derived from the containing class.

For a comparison of internalwith the other access modifiers" see Accessibility $evels ',

eference)and Access &odifiers ', Programming Nuide).

For more information about assemblies" see Assemblies and the Nlobal Assembly ,ache ', and

2isual @asic).

A common use of internal access is in component6based development because it enables a group of

components to cooperate in a private manner without being e*posed to the rest of the applicationcode. For e*ample" a framewor% for building graphical user interfaces could

provide ,ontrol and Form classes that cooperate by using members with internal access. Since these

members are internal" they are not e*posed to code that is using the framewor%.
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t is an error to reference a type or a member with internal access outside the assembly within which

it was defined.

internal members are visible to all code in the assembly they are declared in.'And to other

assemblies referenced using the Tnternals2isible#oU attribute)

private members are visible only to the declaring class. 'including nested classes)For 'hopefully)obvious reasons" an outer 'non6nested) class cannot be declared private.

#o answer the 1uestion you forgot to as%" protected members are li%e private members" but are also

visible in all classes that inherit the declaring type. '@ut only on an e*pression of at least the type of

the current class) 88 Assebl!%.cs

88 Copile $ith* 8target*librar!

internal class 3aseClass

{

public static int intM - ;

}

#he static constructor will be call the first time an object of the type is instantiated or a static

method is called. And will only run once

#he public constructor is accessible to all other types

#he internal constructor is only accessible to types in the same assembly

On top of these three thereKs also protected which is only accessible to types derived from the

enclosing type

and protected internal which is only accessible to types in the same assembly that derives from the

enclosing type

and private which is only accesible from the type it self or any nested types

a static constructorwill be called the first time the class is accessed statically.

a constructor with an internalaccess modifier can only be called by items that meet the

criteria for internal" which is Jaccessible only within files in the same assemblyJ.

a constructor with an publicaccess modifier can be accessed by anything

and so on. protected and private constructors operate as you e*pect 6 the constructors are

accessible to items that meet the criteria for the access modifier.

Seale( 8lass

Sealed classes are used to restrict the inheritance feature of ob%ect oriented programming. !nce a classis defined as a sealed class, the class cannot be inherited.

$n C#, the sealed modifier is used to define a class as sealed. $n (isual )asic .*Tthe *ot$nheritable"eyword serves the purpose of sealed. $f a class is derived from a sealed class then the

compiler throws an error.

$f you have ever noticed, structs are sealed. +ou cannot derive a class from a struct.

The following class definition defines a sealed class in C#

88 ealed class

sealedclassealedClass{
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}$n the following code, $ create a sealed class SealedClass and use it from Class-. $f you runthis code then it will wor" fine. )ut if you try to derive a class from the SealedClass, you will

get an error.using!ste;classClass%{

staticvoidMain(string+, args)

{

ealedClasssealedCls - ne$ealedClass(); inttotal - sealedCls.Add(& >);

Console.WriteLine("#otal - " total.#otring());

}}88 ealed class

sealedclassealedClass{

publicintAdd(int@& int!) {

return@ !; }}MSDN Updated

Sealed Methods and PropertiesYou can also use the sealed modifier on a method or a property that overrides a virtual

method or property in a base class. This enables you to allow classes to derive from your classand prevent other developers that are using your classes from overriding specific virtualmethods and properties.

classD

{

protectedvirtualvoid7() { Console.WriteLine("D.7"); }

protectedvirtualvoid7'() { Console.WriteLine("D.7'"); }

}

classE * D

{

sealedprotectedoverridevoid7() { Console.WriteLine("E.7"); }

protectedoverridevoid7'() { Console.WriteLine("D.7:"); }

}

classF * E

{

88 Attepting to override 7 causes copiler error C':=.

88 protected override void 7() { Console.WriteLine("C.7"); }

88 9verriding 7' is allo$ed.

protectedoverridevoid7'() { Console.WriteLine("F.7'"); }

}

Why Sealed Classes?


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We %ust saw how to create and use a sealed class. The main purpose of a sealed class is tota"e away the inheritance feature from the user so they cannot derive a class from a sealedclass. !ne of the best usage of sealed classes is when you have a class with static members.or example, the /&ens/and /)rushes/ classes of the /System.0rawing/ namespace.

The &ens class represents the pens for standard colors. This class has only static members. orexample, /&ens.)lue/ represents a pen with the blue color. Similarly, the /)rushes/ class

represents standard brushes. /)rushes.)lue/ represents a brush with blue color.So when you're designing your application, you may "eep in mind that you have sealed classesto seal the user's boundaries.

$n the next article of this series, $ will discuss some usage of abstract classes.

,lasses can be declared as sealed. #his is accomplished by putting the sealed %eyword before the

%eyword class in the class definition Sealed classes are used to restrict the inheritance feature of

object oriented programming. Once a class is defined as sealed class" this class cannot be inherited.

A sealed class cannot be used as a base class. For this reason" it cannot also be an abstract class.

Sealed classes are primarily used to prevent derivation. @ecause they can never be used as a baseclass" some run6time optimi-ations can ma%e calling sealed class members slightly faster.

Partial 8lass

There are several situations when splitting a class definition is desirable:

'hen wor$ing on large pro"ects, spreading a class over separate files enables multiple

programmers to wor$ on it at the same time.

'hen wor$ing with automatically generated source, code can be added to the class

without having to recreate the source file. *isual +tudio uses this approach when it creates'indows Forms, 'eb service wrapper code, and so on. #ou can create code that uses these

classes without having to modify the file created by *isual +tudio.

To split a class definition, use the partial$eyword modifier, as shown here:

public partial class mployee{

public void oWor6()

{

}

}

public partial class Bplo!ee

{

public void 4o#oLunch()

{

}

}

#he partial%eyword indicates that other parts of the class" struct" or interface can be defined in the

namespace. All the parts must use the partial%eyword. All the parts must be available at compile

time to form the final type. All the parts must have the same accessibility" such as public" pri'ate"

and so on.

f any part is declared abstract" then the whole type is considered abstract. f any part is declaredsealed" then the whole type is considered sealed. f any part declares a base type" then the whole

type inherits that class.

All the parts that specify a base class must agree" but parts that omit a base class still inherit the
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base type. Parts can specify different base interfaces" and the final type implements all the interfaces

listed by all the partial declarations. Any class" struct" or interface members declared in a partial

definition are available to all the other parts. #he final type is the combination of all the parts at

compile time.

The following are merged from all the partial&type definitions:

-/ comments

interfaces

generic&type parameter attributes

class attributes

members

;here are se'eral rules to follo, ,hen you are ,or+in) ,ith partial class (efinitions9

All partial6type definitions meant to be parts of the same type must be modified

with partial. For e*ample" the following class declarations generate an error:publicpartialclassA { }

88public class A { } 88 Brror& ust also be ar6ed partial

#he partialmodifier can only appear immediately before the %eywords class" struct"

or interface.

/ested partial types are allowed in partial6type definitions as illustrated in the following

e*ample:

partialclassClassWithNestedClass

{

partialclassNestedClass { }

}

partialclassClassWithNestedClass

{

partialclassNestedClass { }

}

All partial6type definitions meant to be parts of the same type must be defined in the same assembly

and the same module '.e*e or .dll file). Partial definitions cannot span multiple modules.

#he class name and generic6type parameters must match on all partial6type

definitions. Neneric types can be partial. Each partial declaration must use the same

parameter names in the same order.

#he following %eywords on a partial6type definition are optional" but if present onone partial6type definition" cannot conflict with the %eywords specified on another

partial definition for the same type:

public

private

protected

internal

abstract

sealed

base class

new modifier 'nested parts)

generic constraints

he biggest use o partial classes is make lie easier on code generators designers. Partial classes
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allow the generator to simpl# emit the code the# need to emit and do not ha&e to deal with user edits tothe ile. 5sers are likewise ree to annotate the class with new members b# ha&ing a second partialclass. his pro&ides a &er# clean ramework or separation o concerns.

A better wa# to look at it is to see how designers unctioned beore partial classes. he %in1orms

designer would spit out all o the code inside o a region with strongl# worded comments about not

modi#ing the code. /t had to insert all sorts o heuristics to ind the generated code or later processing.

6ow it can simpl# open the designer.cs ile and ha&e a high degree o conidence that it contains onl#code relati&e to the designer.

Advantages of a 0artial 1lass

2ere is a list of some of the advantages of partial classes:

;.#ou can separate 3I design code and business logic code so that it is easy to read and understand. For

example, you are developing a web application using *isual +tudio and add a new web form then there

are two source files, 4aspx.cs4 and 4aspx.designer.cs4. These two files have the same class with

the partial $eyword. The 4.aspx.cs4 class has the business logic code while 4aspx.designer.cs4 has user

interface control definition.


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Partial methods are intended to solve a major problem that is not only caused by code-generation tools

and also affects those same tools. For instance, you are writing a code-generation tool but want to

provide a way for the developers that are using your generated classes to hook in to specific areas of

the code. As such, you don't want them editing your generated code since those customizations will be

lost the next time the tool runs. On the flip side of this scenario is the developer who needs to write the

code that hooks into those specific areas and doesn't want that code being lost the next time the tool

runs.

Delegates are one solution to this type of problem. In the generated code, you declare a delegate

method that you then call at the appropriate areas. If no one has implemented a concrete version of the

delegate, the call will not do anything. However, if someone has implemented am instance of that

delegate then the call will run the code in that instance. This sounds like a pretty good solution, and,

until partial methods it really was the only solution. The drawback is that the code for the delegate is

always compiled in to the runtime of your application and add to the runtime overhead of application

(granted, that overhead is minimal but it's still there).

Partial classes helped with this problem by allowing the code-generation tools to isolate the generatedcode in a partial class. This allowed the developer to add their own methods to the class without fear

that they would be overwritten the next time the tool ran. However, it only helped partially. In order to

accomplish our scenario, you still needed to provide a delegate to allow the developer to hook into your

process.

If we take this a step further and look at partial methods, you will start to see how they work and what

the benefit is of using them. The following rules govern how partials methods can be declared and

used:

1.Must be declared inside a partial class.


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without committing to actual data t#pes. his results in a signiicant perormance boost and higher3ualit# code, because #ou get to reuse data processing algorithms without duplicating t#pe'speciiccode. /n concept, generics are similar to !99 templates, but are drasticall# dierent in implementationand capabilities.1enerics provide the solution to a limitation in earlier versions of the common languageruntime and the C# language in which generali2ation is accomplished by casting types to andfrom the universal base type !b%ect. )y creating a generic class, you can create a collectionthat is type-safe at compile-time.

The limitations of using non3generic collection classes can be demonstrated by writing a shortprogram that ma"es use of the .rray#istcollection class from the .*T ramewor" base class

library. .rray#istis a highly convenient collection class that can be used without modification

to store any reference or value type.

using System;using System!Collections;using System!Collections!eneric;using System!0e,t;

namespace enerics

/ class eneric#ist / static void Main(string< args / // The .NET Framework 1.1 way to create a List .rray#ist list = ne% .rray#ist(;

77 .dd an integer to t-e #ist list!.dd(>;

77 .dd a string to t-e #ist! 0-is %ill compile? 77 but may cause a Runtime +rror@

list.Add("This will trigger a Runtime Error"!

77 e cast to int? but t-is %ill causes an )nvalidCast+,ception 77 %-en encounter a string in t-e #ist! int t # (int!list$1%

t = A; foreac- (int , in list / t 9= ,; }

// The .NET Framework &.' way to create a List

Listint) list1 # new Listint)(!

77 No bo,ing? no casting listB!.dd(>; listB!.dd(B;

77 Compile5time error listB!.dd("0-is %ill trigger a Compile5time +rror@";

77 et t-e values from t-e #ist? no casting int t1 # list1$1%

tB = A;

foreac- (int , in listB / tB 9= ,; }


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} }}

Genericsallow you to delay the specification of the data type of programming elements in a class

or a method" until it is actually used in the program. n other words" generics allow you to write a

class or method that can wor% with any data type.

Dou write the specifications for the class or the method" with substitute parameters for data types.Bhen the compiler encounters a constructor for the class or a function call for the method" it

generates code to handle the specific data type. A simple e*ample would help understanding the

concept:

@eatures of Generics

sing generics is a techni1ue that enriches your programs in the following ways:

t helps you to ma*imi-e code reuse" type safety" and performance.

Dou can create generic collection classes. #he ./E# Framewor% class library contains several new

generic collection classes in the System.Collections.Genericnamespace. Dou may use these generic

collection classes instead of the collection classes in the System.Collectionsnamespace.Dou can create your own generic interfaces" classes" methods" events and delegates.

Dou may create generic classes constrained to enable access to methods on particular data types.

Dou may get information on the types used in a generic data type at run6time by means of

reflection.

Introduction to Generic Collections

4ll the way bac" in 5esson 67, you learned about arrays and how they allow you to add and retrieve acollection of ob%ects. 4rrays are good for many tas"s, but C# v7.6 introduced a new feature calledgenerics. 4mong many benefits, one huge benefit is that generics allow us to create collections that allow

us to do more than allowed by an array. This lesson will introduce you to generic collections and how theycan be used. 8ere are the ob%ectives for this lesson

9nderstand how generic collections can benefit you

5earn how to create and use a generic 5ist

Write code that implements a generic 0ictionary

What Can Generics Do For Me?

Throughout this tutorial, you've learned about types, whether built3in :int, float, char; or custom

:Shape, ustomer,!ccount;. $n .*T v-.6 there were collections, such as the!rray"istfor wor"ing with

groups of ob%ects. 4n!rray"istis much li"e an array, except it could automatically grow and offeredmany convenience methods that arrays don't have. The problem with!rray"istand all the other .*Tv-.6 collections is that they operate on typeob#ect. Since all ob%ects derive from the ob#ecttype, you can

assign anything to an!rray"ist. The problem with this is that you incur performance overhead convertingvalue type ob%ects to and from the ob#ecttype and a single!rray"istcould accidentally hold different

types, which would cause hard to find errors at runtime because you wrote code to wor" with one type.1eneric collections fix these problems.

4 generic collection is strongly typed :type safe;, meaning that you can only put one type of ob%ect intoit. This eliminates type mismatches at runtime. 4nother benefit of type safety is that performance isbetter with value type ob%ects because they don't incur overhead of being converted to and fromtype ob#ect. With generic collections, you have the best of all worlds because they are strongly typed, li"earrays, and you have the additional functionality, li"e!rray"istand other non3generic collections, withoutthe problems.

The next section will show you how to use a generic "istcollection.


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8reatin) GenericList8ollections

#he pattern for using a genericistcollection is similar to arrays. Dou declare theist" populate its

members" then access the members. ereKs a code e*ample of how to use a ist:

$ist(int+ mynts new $ist(int+')5

mynts.Add';)5 mynts.Add'


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#he difference between ./E# $ists and arrays is that lists can have elements added to them 66 they

grow to be big enough to hold all of the re1uired items. #he list stores this internally in an array

and" when the array is no longer big enough to hold all of the elements" a new array is created and

the items copied across.

$ist 4 arrays both implement Enumerable. #hatKs how interfaces wor% 66 classes implement the

contract and behave in a similar fashion and can be treated similarly as a result 'you %now that theclass implements Enumerable" you donKt need to %now the hows or the whys). suggest you read

up on interfaces and so forth.

1Bnuerableis a general'purpose interace that is used b# man# classes, such

as Arra!, Listand tringin order to let someone iterate o&er a collection. :asicall#, it4s what dri&es

the 0oreachstatement.

1Listis t#picall# how #ou e"pose &ariables o t#pe Listto end users. his interace permits random

access to the underl#ing collection.

"Enuerable

Enumerable(#+ represents a series of items that you can iterate over 'using foreach" for e*ample)

Enumerable doesnKt have the ,ount method and you canKt access the collection through an inde*

'although if you are using $/V you can get around this with e*tension methods).

Enumerable is a general6purpose interface that is used by many classes" such as Array" $ist and

String in order to let someone iterate over a collection. @asically" itKs what drives the foreach

statement.

As a rule of thumb you should always return the type thatKs highest in the object hierarchy that

wor%s for the consumers of this method. n your case Enumerable(#+.

"Hist

$ist(#+ is a collection that you can add to or remove from.

$ist has count method and accessed using inde*.

$ist is typically how you e*pose variables of type $ist to end users. #his interface permits random

access to the underlying collection.

f the consumers of the class need to add elements" access elements by inde*" remove elements you

are better off using an $ist(#+.

2ashTable

2ashtable optimi9es loo$ups. It computes a hash of each $ey you add. It then uses this hash code to

loo$ up the element very uic$ly. It is an older .5T Framewor$ type. It is slower than the

generic ictionar!type.

using+ystem.1ollections;class2rogra

{

staticGashtable 4etGashtable()

{

//Create and return new #ashtable$ Gashtable hashtable - ne$Gashtable(); hashtable.Add("Area"& %); hashtable.Add("2erieter"& >>);


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hashtable.Add("Mortgage"& >); returnhashtable;

}

public staticvoidMain()

{

Gashtable hashtable - 4etGashtable();

//%ee if the #ashtable contains this key$ Console.WriteLine(hashtable.Contains?e!("2erieter")); //Test the Contains method$ !t works the same way$ Console.WriteLine(hashtable.Contains("Area")); //&et value of Area with inde'er$ intvalue - (int)hashtable+"Area",; //(rite the value of Area$

Console.WriteLine(value);

}

}

Dictionary

A dictionary is used where fast loo$ups are critical. The ictionar!type provides fast loo$ups with$eys to get values. 'ith it we use $eys and values of any type, including ints and strings. Dictionary

reuires a special syntax form.

Dictionary is used when we have many different elements. 'e specify its $ey type and its value type. It

provides good performance.

classDict

{

staticvoidMain()

{

//)'ample "ictionary again

ictionar!Hstring& intI d - ne$ictionar!Hstring& intI() {

{"Lion"& '}& {"dog"& %}}; //*oop over pairs with foreach 0oreach(?e!Jalue2airHstring& intI pair ind)

{

Console.WriteLine ("{}& {%}"&pair.?e!& pair.Jalue);

}

0oreach(varpair ind)

{

Console.WriteLine("{}& {%}"& pair.?e!& pair.Jalue);

}

Console.5ead?e!();

}

}

Dictionary:

It returns error if we try to find a $ey which does not exist.

It is faster than a 2ashtable because there is no boxing and unboxing.

nly public static members are thread safe.

Dictionary is a generic type which means we can use it with any data type.

Hashtable:

It returns null if we try to find a $ey which does not exist.


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It is slower than dictionary because it reuires boxing and unboxing.

All the members in a 2ashtable are thread safe,

2ashtable is not a generic type,

Dou use a hashtable 'dictionary) when you want fast loo% up access to an item based on a %ey.

f you are using $ist" $ist or Enumerable generally this means that you are looping over data 'well

in the case of Enumerable it definitely means that)" and a hashtable isnKt going to net you anything.

/ow if you were loo%ing up a value in one list and using that to access data in another list" that

would a little different. For e*ample:

;.Find position in list of tem foo.


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#ypes of inheritance in c

#here are C types of inheritance as shown below.

;.Single nheritance


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&ultilevel nheritance

Bhen a derived class is created from another derived class or let me put it in this way that a class is

created by using another derived class and this type of implementation is called as multilevel

nheritance

E*ample of &ultilevel nheritance

; classeadOffice8

ust3$n3Time :>$T; compiler.

What is Manifest?

4ssembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the following

things

(ersion of assembly.

Security identity.

Scope of the assembly.


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State the differences *et"een the +is,ose(!and Finali-e(!.

C5< uses the 0ispose and inali2e methods to perform garbage collection of run3time ob%ects of .*T

applications.

The inaliDemethod is called automatically by the runtime. C5< has a garbage collector :1C;, which

periodically chec"s for ob%ects in heap that are no longer referenced by any ob%ect or program. $t callsthe inali2e method to free the memory used by such ob%ects. The *isposemethod is called by the

programmer.*isposeis another method to release the memory used by an ob%ect. The 0ispose method

needs to be explicitly called in code to dereference an ob%ect from the heap. The *isposemethod can be

invo"ed only by the classes that implement the )*isposableinterface.

What is code access security 'C+S(?

Code access security :C4S; is part of the .*T security model that prevents unauthori2ed access of

resources and operations, and restricts the code to perform particular tas"s.

Differentiate *et"een mana)ed and unmana)ed code?

Managed code is the code that is executed directly by the C5< instead of the operating system. The code

compiler first compiles the managed code to intermediate language :$5; code, also called as MS$5 code.

This code doesn't depend on machine configurations and can be executed on different machines.

9nmanaged code is the code that is executed directly by the operating system outside the C5$T compiler is an important element of C5$T compiler translates the MS$5 code of an assembly and uses the C&9 architecture of the target

machine to execute a .*T application. $t also stores the resulting native code so that it is accessible for

subseuent calls. $f a code executing on a target machine calls a non3native method, the >$T compiler

converts the MS$5 of that method into native code. >$T compiler also enforces type3safety in runtime

environment of .*T ramewor". $t chec"s for the values that are passed to parameters of any method.

or example, the >$T compiler detects any event, if a user tries to assign a ?73bit value to a parameter

that can only accept B3bit value.

What is difference *et"een *ystem.*tringand *ystem.*tringuilder classes?

Stringand String&uilderclasses are used to store string values but the difference in them is thatString is immutable :read only; by nature, because a value once assigned to a String ob%ect cannot be

changed after its creation. When the value in the String ob%ect is modified, a new ob%ect is created, in

memory, with a new value assigned to the Stringob%ect. !n the other hand, the String&uilderclass


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is mutable, as it occupies the same space even if you change the value. The String&uilderclass is

more efficient where you have to perform a large amount of string manipulation.

Descri*e the roles of C$1 in .N! Frame"or.

C5< provides an environment to execute .*T applications on target machines. C5< is also a common

runtime environment for all .*T code irrespective of their programming language, as the compilers ofrespective language in .*T ramewor" convert every source code into a common language "nown as

MS$5 or $5 :$ntermediate 5anguage;.

C5< also provides various services to execute processes, such as memory management service and

security services. C5< performs various tas"s to manage the execution process of .*T applications.

The responsibilities of C5< are listed as follows

4utomatic memory management

1arbage Collection

Code 4ccess Security

Code verification >$T compilation of .*T code

What is the difference *et"een int and int23.

There is no difference between intand int>F. System!)nt>Fis a .*T Class and intis an alias name

forSystem!)nt>F.

SP.:E;

Concept of Postback in ASP!"$

A postbac$ is a reuest sent from a client to server from the same page user is already wor$ing with.A+0.5T was introduced with a mechanism to post an 2TT0 0+T reuest bac$ to the same page. It(s

basically posting a complete page bac$ to server


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"nit8oplete9

#rac%ing of the 2iewState is turned on in this event.

Any changes made to the 2iewState in this event are persisted even after the ne*t postbac%.

PreHoa(9

#his event processes the postbac% data that is included with the re1uest.

Hoa(9

n this event the Pageobject calls the On$oadmethod on the Pageobject itself" later the On$oadmethod of thecontrols is called.

#hus $oadevent of the individual controls occurs after the $oadevent of the page.

8ontrolE'ents9

#his event is used to handle specific control events such as a @uttoncontrols ,lic%event or

a #e*t@o*controls #e*t,hangedevent.n case of postbac%:

f the page contains validator controls" the Page.s2alidproperty and the validation of the controls ta%es placebefore the firing of individual control events.

Hoa(8oplete9

#his event occurs after the event handling stage.

#his event is used for tas%s such as loading all other controls on the page.

Preen(er9

n this event the Preenderevent of the page is called first and later for the child control.sage:

#his method is used to ma%e final changes to the controls on the page li%e assigning the 0ataSourcedand

calling the 0ata@indmethod.

Preen(er8oplete9

#his event is raised after each controlKs Preenderproperty is completed.

Sa'eState8oplete9

#his is raised after the control state and view state have been saved for the page and for all controls.

en(er8oplete9

#he page object calls this method on each control which is present on the page.

#his method writes the controls mar%up to send it to the browser.


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+ection vent Description

be raised on each reuest.

GttpModule Authenticate5eKuest

This event signals that A+0.5T runtime is ready to

authenticate the user. Any authentication code can

be in"ected here.

GttpModule Authorie5eKuest This event signals that A+0.5T runtime is ready toauthori9e the user. Any authori9ation code can be

in"ected here.

GttpModule 5esolve5eKuestCache

In A+0.5T, we normally use outputcache directive to

do caching. In this event, A+0.5T runtime

determines if the page can be served from the cache

rather than loading the patch from scratch. Any

caching specific activity can be in"ected here.

GttpModule AcKuire5eKuesttate

This event signals that A+0.5T runtime is ready to

acuire session variables. Any processing you would

li$e to do on session variables.

GttpModule 2re5eKuestGandlerB@ecute

This event is raised "ust prior to handling control to

the GttpGandler. !efore you want the control to be

handed over to the handler any pre&processing you

would li$e to do.

GttpGandler 2rocess5eKuest

Gttphandler logic is executed. In this section, we

will write logic which needs to be executed as per

page extensions.

2age 1nit

This event happens in the A+0.5T page and can be

used for:

1reating controls dynamically, in case you have

controls to be created on runtime.

Any setting initiali9ation.

aster pages and the settings.

In this section, we do not have access to viewstat

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