Top 50 OOPS C# Interview Questions - .NET

[@rakeshshettigar2817]

Hi Sir. This question bank helped me a lot to clear more than 5 interviews where I was finding difficulty in clearing one interview, a great salute to you for helping in building someone's career. Will keep supporting you💗🙂

[@interviewhappy]

Well done and Congrats Rakesh.... May you keep getting success in your career in future.

[@kiranpylla]

Hello rakesh, can you please share you interview experience. and how to get new job. at present i am working with dotnet technology only, but unable to take out preparation time. Can we form any group and discuss there.

[@bluesparrow2.027]

Hi sir I cleared first round but I'm getting problem in second round like practical round if u guide about practical round plss it's humble request

[@AbhaySingh-lf4oy]

@@kiranpyllayes definitely make a group

[@girijaprasad7517]

​@@AbhaySingh-lf4oyi am also in. Let's connect Nd form a group

[@jyothisikhinam6030]

i'm preparing for interviews ...by watching your vedios sir... tqq so much these are very helpful..to growup

[@interviewhappy]

Thanks Jyothi and all the best for your career.

[@isharasamintha-csc]

Hi Happy, Your videos(Angular,SQL,OOP,.Net Core) was very helpful to me to get the new position. Thank You♥♥

[@interviewhappy]

Great... congrats man.... enjoy the moment. Happy is happy for you.

[@NavinKumar-pm2ec]

This is great Man. Very Nice explanation. Every one should go once at least once for quick revision. Salute.💛💛

[@interviewhappy]

Thanks Navin, Appreciate you liked it.

[@kuldeepbhatt5273]

​@@interviewhappyhow to contact with you?

[@rihamhossain9662]

You are so amazing with this question. You teach this concept so easily that no can do that. I understand so many things from you. Thank you sir . 😀

[@interviewhappy]

Thanks for appreciating my friend your words are very kind and means a lot to me. Thank you much @rihamhossain9662

[@hareeshponnam1661]

Really best explanation for each every question. Thank you very much your videos. I'm always thankful you 🙏

[@interviewhappy]

Thanks Hareesh. All the best if you are preparing for interviews.

[@mocococo2877]

Thank you for your nice tutorial. I am finishing the first hour. For the moment I have two little notes. I think members of the interface do not have access specifiers and I think I have seen books saying that interfaces can also have property members and events. I also think that the main reason for boxing and unboxing was to achieve universal data type - object, which could be send as params to any class ctors and methods. Then generics came and send those to the unemployment department.

[@catherineberkmans6734]

This is a fantastic video and helped me quickly brush-up the concepts. I loved the delegated part. This was by far the simplest explanation of it I have heard of...👏

[@interviewhappy]

Great to hear and Thanks @catherine

[@babarmughal8891]

Just want to say, amazing

[@interviewhappy]

Thanks Babar. Glad you liked it. All the best for your career.

[@babarmughal8891]

@@interviewhappy Well, I am a software engineer doing job. I watched your video to clear OOP Concepts. Thank you for mind blowing content. Keep posting stuff like that.

[@vikrambardhan644]

Thank you so much. very nice explanation with examples. it consolidated everything at single place. so no need to go other place. once again thank you so much.

[@interviewhappy]

Thanks Vikram... I appreciate you liked it..

[@roshanpoudel2594]

Perfect...it clears all of my doubt...hats off...keep it up !!

[@farhataliksp]

IEnumerable Interface should be used for the IN Memory object Collection to fetch the data while IQuerable should be used when you are fetching the from the resources like DbContext , XML etc because if you want the collect the data on filter criteria then IQuerable useful in this case.

[@mohamedsilmy5294]

one of the best ever interview guide for any discipline I came across. Hats off to you sir.

[@interviewhappy]

Glad it was helpful @mohamedsilmy5294

[@suryakantdixit2721]

thanks for your effort that you put togethor all imp questions in one video

[@developerrihab7993]

Wooooow excellent explaination ... i encourage you to continue ..make us a design pattern video I couldn't find any good one

[@interviewhappy]

Thanks, sure

[@PrashantYadav-kz2xo]

❤

[@anixop9606]

No one can explain like this 👍

[@interviewhappy]

Thanks

[@gopinivas]

Now I am able to clear the interview after seeing your video.thanks

[@interviewhappy]

You are most welcome. All the Best Gopi

[@entusiast2000]

About encapsulation: you could add an example of errornous direct assign of experience to a negative value and add checks to a setter to show why the property setter is needed. Trivial setter just slows the things.

[@interviewhappy]

Yes that is one good example

[@CyberWorldReality]

Amazing work. Probably the best c# video to date!

[@interviewhappy]

Wow, thanks!

[@gatemcq5226]

Superb interview series of question with explanation.

[@Meenukrishnaarun]

Very nice explanation..thank you so much sir🙏

[@interviewhappy]

wc Meenu and all the best for your career.

[@nileshmakwana4060]

Great

[@fInDmEbRuh]

Interface can contain not only methods but also properties, events and indexers with signature only.

[@sreenivasareddyganta2689]

Very nice explanation sir, thank you for bringing this it will be very helpful during the c# interview.

[@interviewhappy]

Thanks Sreeni... Sounds great this helped you

[@jamunadevi7635]

Hi sir ..Can you provide questions for 5+ years experience vb.net and asap.net. Thanks

[@interviewhappy]

@@jamunadevi7635 I love vb.net. worked in it a lot. But now a days its not in demand. But soon i will try to make some content for it.

[@touseefghazanfar8487]

You are an amazing teacher. Hats Off.

[@interviewhappy]

Thanks Touseef and all the best for your career man.

[@Sravanth_KidsGames]

It's very useful for most of the questions covered from the material. Nice explanation in videos. Happy you tube channel and questpond you tube channel is enough to crack the interview for 2 to 4 year experience level of dotnet developer. Mostly 80 % expected questions. But presenting the level we need to practice

[@vaninadhs8260]

Excellent Bro. Well-articulated and examples . Thanks it helps

[@interviewhappy]

Glad it was helpful!

[@crazyyouthyoutubechannel6309]

You are like... A textbook... 😍

[@interviewhappy]

Thanks man

[@mmaranta785]

I’m learning so much from your videos.

[@interviewhappy]

That's great, thanks Maranta

[@kalaiselvanarchunan4678]

2.29.23 Delegate example , really SUPER

[@interviewhappy]

Thanks Archu

[@makinibryan]

Awesome video, very informative!

[@interviewhappy]

Thanks Bryan. All the best for your career.

[@makinibryan]

@@interviewhappy Thanks!

[@engineersINnight]

Good FAQs

[@padmaraj690]

Thanks a ton for your effort. You are helping the techies to land their dream jobs.

[@interviewhappy]

Thanks Raj. Yes my goal is to help the candidates in their interview process.

[@deepakgupta5733]

Masterpiece 👍💖✨⭐✌️👏👌

[@interviewhappy]

Thanks Deepak

[@pixelvlog666]

thanks man . you helped me so much thank you again and again

[@interviewhappy]

welcome

[@Aparna.Ratheesh]

Hi Sir, Thankyou for the detailed class. But 1 correction - In C#, the default access specifier for class members (fields, methods, properties, etc.) is private. If no access modifier is specified, members are implicitly considered private.

[@interviewhappy]

Yes, you are right

[@rajendarraj7661]

No words to explain, appreciate the effort keepup the good work

[@interviewhappy]

Thanks Raj

[@khanfaizan05]

Happy sir.. thank you so much.. i watched your video and purchased an interview course on udemy for preparation and revision.. Finally got the offer.. Thank you so much .. Lots of love and respect.. Keep up the good work. ❤❤

[@interviewhappy]

Congratulations to my friend. This achievement is a result of your hard effort and never-give-up attitude.

[@ashrafkhan2958]

good job male, thanks!

[@interviewhappy]

welcome Ashraf. All the best.

[@interviewhappy]

welcome Ashraf. All the best.

[@mridulpaul1378]

Thank you for your nice tutorial. An interface can have properties as well.

[@souravsinha2926]

Thank you for explaining. Can overloading achieve by different return type

[@interviewhappy]

No Sourav, different return type, same parameters will lead to error.

[@uddhavmhatre4627]

Hi,Nice video.. you explain everything in detail.

[@interviewhappy]

Thank you so much 🙂

[@widozein]

Thanks a lot! This is really helpful

[@anupamsharma7495]

Very good video. It includes everything for revision purpose. Kindly make a video on .Net Core also. Thanks.

[@interviewhappy]

Thanks Anupam, I already post a video on .NET Core also. Please check videos in my channel.

[@techielovekid6121]

01:05:00 Boxing & Unboxing literally confused. Why should we used this in our OOP concepts? And is object keyword here?

[@alicebeni]

Thank you so much!!!!! It is very useful

[@interviewhappy]

welcome Alice

[@jt.633]

2:34:17 I'm not sure if this is important but why did you initialize the delegate outside of the program class? Thank you you're the best C# interview teacher out there, I only watch yours!

[@proxi_Laundasdasd]

becz deligates are meant to be used from outside classes. They work as a representative of things happening inside class.. So that anyone who wants to use them do not need to create instance of that class to use the delegate. instead they can directly call it and use it.

[@eshwarmoorthy8071]

Thank you sir for providing such a valuable resource

[@interviewhappy]

Thanks and welcome Eshwar Moorthy

[@permallavennela2797]

Thank you so much your videos sir please make one video on upcasting and downcasting

[@ashvinitambe3023]

hello sir plzz provide web api concept video and how it is created and also provide fresher level interview video. i like ur video and explanation.

[@interviewhappy]

Thanks Ashvini. I poted a web api interview question series also. In starting questions, I have explained why web api is needed.

[@rajatnagpure7445]

even after 2x it seems slow! Great Content Though👍

[@interviewhappy]

Thanks Rajat. I will try to increase speed from my side.

[@sayankolay6639]

1:23:20 what is the need of finally block in try catch ? If we write the code what inside in the finally block after the catch block the code will excecute same as finally block so, what makes "finally" so important?

[@khushaliporwal2582]

There are some scenarios where code written directly below a catch block might not execute as below: 1. If an exception is not handled within the catch block and is instead propagated, any code written after the catch block will not execute. 2. If a return statement is executed in the try or catch block, the control flow will exit the method, and the code following the catch block will not execute. 3. If the method exits due to an exception, and there is no higher-level exception handler, the code following the catch block will not execute. The finally block executes no matter what happens in the try or catch blocks, including exceptions, return statements, or method termination.

[@FunAndCreativeCorner]

Excellent video. Thank you sir.

[@interviewhappy]

Glad it was helpful!

[@savithavadlagatta9379]

Hi Sir, I have a question which was asked by an interviewer, what is the of the constructor in Abstract class.plz give me one example sir. and one more question is why do we need static fields/methods/constructors in application.what is the use of the that static thing.plz explain with example sir.

[@vTFT2]

such great effort bro.. really appreciate it!! :) those examples were really helpful in relating to use case...! this was awesome man!!

[@interviewhappy]

Thanks Vipul, wish you all the best for your career.

[@ralphpurtcher]

This video leaves me feeling quite discombobulated after listening to its definitions of the terms abstraction and encapsulation!! The video gives the defintion of abstraction as "Showing only required things". But that definition matches the Wikipedia definition for encapsulation, Wikipedia states encapsulation as being "the limiting of direct access to some of that data". I'm familiar with a very different definition of abstraction, which is the one you'll also find in the Webster dictionary, which is "disassociated from any specific instance".

[@AmitKumar-ib7lc]

thanks a lot sir u r super

[@interviewhappy]

Thanks Amit. All the best for your career.

[@theo-ov1vk]

if i pass my interview tomorrow i will donate you 50$ haha , thank you , really great job

[@interviewhappy]

You will definitely pass Theo. My best wishes are with you.

[@theo-ov1vk]

@@interviewhappy I got the job today, you owe me fifty dollars

[@ak_spotlight]

17. What are Access Specifiers What is the default access modifier in a Class? What is the Other CODE?

[@hadargabbay]

great video! keep up with the great work :)

[@noranora847]

Thank you so much for great explanation!

[@interviewhappy]

Your most welcome for appreciating @noranora847

[@srishti_dixit]

At 2:29:22 if we want to do multiply also then we should again create object?

[@rhuturajtakle3518]

Hi sir, in abstraction examples i have doubt ( 18:06 ) like we can still access calculateHra() method and calculateBasicSalary() method. So how we can achieve abstraction here. Can you please explain. Because one of the interviewer asked me.

[@Kudaty1407]

Those methods should be PRIVATE. I hade the same question come into my head

[@PANDURANG99]

13:23 where is baseclass 2 in case of multilevel inheritance? might be a mistake there

[@crazyyouthyoutubechannel6309]

I think Comment is not enough... But from my side... Take a bow man.....

[@interviewhappy]

I think thanks is not enough. Wish you all the very very best for your career bro.

[@murtazotoshniyozov4688]

Thank you sir for providing with this valuable resource)

[@AbhishekGupta-zf4em]

thanks Man, you are a gem :)

[@interviewhappy]

Thanks Abhishek

[@laxmankere9479]

Dear sir, can you make logical program series which should be contain 50 program based on String, Array, Collection...or if you have already please share link...i am automation Tester

[@anandhakumarjayarajan5498]

Can you explain Interface and Abstract class C# 8 version?

[@interviewhappy]

interface can have method bodies from C# 8. That is the biggest difference. Rest I will explain in some future videos.

[@111niloy222]

nice video Sir, one question is there, in abstract class also we can declare method and use it in dervied class , eg. SetSalary() and SetProject() can be only declared in abstract class also, then why should we use interface? Am I missing something?

[@interviewhappy]

Because later if you want to do multiple inheritance than it is only possible via interfaces not via abstract classes.

[@111niloy222]

@@interviewhappy yes sir, got it now

[@BalwantDhanda]

superb

[@interviewhappy]

Thanks Balwant

[@BalwantDhanda]

can you make video on solid principal in c# i didn't found better video

[@YogeshKumar-ok1ht]

very good vedios Sir Keep it up

[@interviewhappy]

Thanks Yogesh

[@gopiyadavmartha1099]

Sir excellent explanation sir.. But video quality little bit low pls sir

[@shobhamahadev118]

I think feilds can be defined in interface as per my memory.. correct me if jts wrong

[@pareshparmar179]

Good explanation

[@sanocycles6642]

In abraction explanation, 19:00 the remaining two methods should be private I guess. CalculateBasicSalary, calculateHRA.

[@interviewhappy]

Thanks Sano, I will check it

[@sanocycles6642]

@@interviewhappy thanks for your reply sir😍

[@HarunRasheed-hv6ck]

Thank you sir

[@interviewhappy]

Welcome Rasheed

[@surendar2721]

Sir Question 22 . Generics class not required object creation ?

[@vigneshvk4940]

Hi @interviewHappy sir. If possible, can you please create one video for explicit calling concepts in multiple inheritance

[@interviewhappy]

Sure will try to do it soon @vigneshvk4940

[@kpadhnan]

Thank you

[@supriyaka2ru622]

Hi sir, can you please provide the interview questions on azure developer

[@interviewhappy]

Right now I don't have but soon I will create on Azure developer also.

[@576prakash]

how communication happen in angular? different types of guards in angular ? dependency injection in angular how it work ? difference between template driven and reactive forms in angular? : use of guards in angular? how to handle server side exception in angular how to handle client side exception in angular ? pipes in angular and how to create a custom pipe ? : c# extenstion methods? : what is the use of interceptor ? Jwt token flow in angular? difference between dynamic and var keyword in c# ? difference between string and string builder ? difference between readonly and constant ? difference between static and singleton ? differene between interface and abstract ? difference between string.equals and == difference between use and run in .net core ? how dependency injection implemented in .net core application ? what is the difference between == and === in javascript ? difference between first and firstordefault and last and lastordefault single and singleordefault in linq what is the difference between async and sync in c#? www.geeksforgeeks.org/c-sharp-how-to-implement-multiple-interfaces-having-same-method-name/ Interface i1{ Void method(); } Interface i2{ Void method(); } Class program{ Which method will call } And also we are having with diffrent params which method will call

[@interviewhappy]

Ok got it these questions.. sure soon I will

[@snehaa.tambade]

Abstract classes should have Protected constructor right ? so when derived class gets instantiated it will invoke the abstract members,? Please clarify

[@prabhatverma955]

Thank you so much sir.

[@interviewhappy]

Most welcome @ prabhatverma955

[@ahmedebrahem1674]

thankyou🥰🥰

[@interviewhappy]

Your Welcome Ahmed Ebrahem

[@microsoftgraphExplorer]

why is throw ex used then? in which case it is beneficial ?

[@interviewhappy]

In some 5% cases, we do not need complete stack info then we can use this.

[@microsoftgraphExplorer]

@@interviewhappy Thank you for the information sir. Your videos are exponentially increasing my knowledge.

[@DanielJebaraj-db6of]

Please make videos about Entity Framework interview questions

[@interviewhappy]

I think I already posted some of them

[@totoro3439]

Sir if the object of an child class is created, will the constructor of its parent class from which its inherited be triggered?

[@interviewhappy]

Good question totoro. Answer is YES. Both parent and child constructors will be called and parent will always be called before child.

[@totoro3439]

Woww, that's awesome, thank you sir

[@muhammadnawaz1925]

I have a question about abstraction you said that client show only nessasary detail in real example i understand butt in programing client show anly view UI page soo we hum kis se hide kerty hain background detail

[@pranjalichaudhari316]

Very nice video Sir but can you make a roadmap to become .net developer for fresher means step by step how to prepare to become .net developer

[@interviewhappy]

Thanks Pranjali, sure

[@igors1953]

Q14 - why don't we just inherit a class and override the method instead here? Is it some kind of "safety feature" that prevents us from implementing the same method the same way in two separate classes?

[@marcelositonio2495]

Thanks Happy!

[@576prakash]

Can you please try to video on above questions incase anything missed

[@interviewhappy]

Sure Bala

[@sreenivasareddyganta2689]

Could you do a video about design patterns and IQs on design pattrens.

[@jayapradajena2031]

Because ur all tutorials are superb and u elaborate each from very basic and understandable 😌😊

[@interviewhappy]

Sure Sreeni.. I will in future

[@Ris-v4w]

i jumped randomly into the video, at 10:35 and i already have an issue.... sorry, but since when do classes inherit interfaces? multiple inheritance works only between interfaces. one interface can inherit multiple interfaces. classes have the obligation of IMPLEMENTING interfaces. only thing you can do is mimic multiple inheritance is by using functionality implemented by other classes and exposing this through your instance, which actually is called composition. so the statement that you can inherit multiple interfaces in a class is incorrect sorry...but finding an error on the first thing i see makes me not want to listen to the rest of it

[@interviewhappy]

You sounds more accurate. But composition is not a very familiar term in C# and what I shared is more popular. Anyways, thanks for correcting me.

[@deepaksamala77]

Hi Happy, Which context we define class as sealed?

[@interviewhappy]

Hi Deepak, When you want any other developer can create the objects of your class but cannot inherit it. Static can be also used but then object creation is not possible.

[@manisekaranp]

C# an abstract class can have multiple interfaces just like any other class

[@girijaprasad7517]

I really need a mentor like you 'HAPPY JI'. Kindly accept my request. I will be grateful to you. One more request - can you please demonstrate on each language by creating a new fresh project. It will be helpful for us to understand on each module as how they interact with each other. And for architect level for whose year of experience is atleast 10years must have the knowledge to work from scratch so kindly request you to provide the inputs. It will be helpful for us in this output driven era. Thanks

[@srushtibhagat4187]

Hello sir can you tell me how to purchase this course? And in this course related books your giving or not?

[@interviewhappy]

Hi Srushti, I have given the course details in the description of video.

[@TheKingofdom]

Happy, really thanks for this. This is so useful. Advice - stop explaining things by saying "This is nothing but ...". That's a wrong English Indians school teach.