Core Java Interview Questions & Answers | Top FAQs Explained! |

[@s49243]

00:06 The pillar of OOPs concept includes encapsulation, inheritance, polymorphism, and abstraction. 02:53 This subpart explains encapsulation, inheritance, and polymorphism in Java. 07:51 Dynamic polymorphism allows multiple implementations of the inventory service 10:25 Overriding static and private methods is not allowed 15:33 Using default methods in Java interfaces for flexible implementation 17:51 Accessing parent property and overriding default methods 22:25 The finalize method is not called if the system GC is done. 24:35 Proper implementation of equals and hashCode methods is necessary to avoid duplicates in collections. 29:25 Compile time exceptions can be handled at compile time 31:51 FileNotFound exception is a checked exception and not a compile time exception. 36:30 Delegating exception handling to next method caller 38:29 Understanding the order of exception hierarchy is important while handling exceptions in Java. 42:48 finally block can be stopped from executing 45:10 String objects can be created using the new keyword or string literal 49:54 String is immutable 52:13 String class is immutable in Java 56:16 String buffer and StringBuilder are mutable, while String is immutable. 58:38 Creating an immutable class: Setter method write only getter method 1:03:23 Demonstrating how to avoid modifying a Date object in Java 1:05:48 Handling mutability in Java objects 1:10:42 Using the clone method to create a separate copy of an object. 1:12:58 It is recommended to use char array instead of String for storing passwords. 1:17:21 Writing custom marker interfaces in Java 1:19:18 The difference between AR list and linked list 1:23:23 Using generics with lists helps in avoiding type cast issues. 1:25:33 Creating a custom AR list to disallow duplicates 1:30:36 Set implementation allows duplicate objects if equals and hashCode methods are not overridden for custom objects. 1:32:58 The contract between equals and hashCode methods determines if duplicate objects are allowed 1:37:42 Sorting objects based on ID and name using Comparable and Comparator 1:40:22 Creating Comparators in Java for sorting objects based on different attributes. 1:45:56 Explanation of custom sorting using comparator 1:48:16 Fail-fast and fail-safe iterators in Java 1:52:42 ConcurrentHashMap is used when parallel thread access and modification is required. 1:54:42 ConcurrentHashMap does not allow adding null keys or values and throws a null pointer exception immediately. 1:58:58 ConcurrentHashMap uses segment locking or bucket locking 2:01:14 ConcurrentHashMap is preferred over Hashtable due to its locking mechanism. 2:05:46 Hing Collision 2:07:54 Hash map internally uses linked list nodes. 2:12:03 Understanding TreeMap in Java 2:14:50 The compareTo() method compares two objects and returns -1, 0, or 1 based on the comparison result.

[@jagrutipatil1020]

Hats off to you buddy 👍

[@Srikanthb4040]

Hats off

[@ezhilarasikrishnan5408]

❤

[@sanjay26031983]

@s49243 Any tool used for this or manually typed😮

[@freakintruder]

​@@sanjay26031983chatgpt probably

[@neonew339]

Thank you for great video. 99% teacher would cover these questions in 20 mins and most of us wouldn't understand anything and end up memorizing the answers. but you have properly explained each and every answer in great detail in 2 hours.

[@PranjaliSuryavanshi-t2o]

Must watch interview questions video for java developers. Everything is explained practically. Thanks a lot.

[@localhero1938]

Thanks for the video brother it helps lot

[@Javatechie]

Thank you so much brother keep learning 😃

[@yatendra__singh]

Rockstar is making some noice in the market ❤

[@Javatechie]

😜😜

[@karthickgunasekaran3220]

Yes rockstar making nice video

[@devarajk6858]

@@Javatechie I have 3.5 years of experience as Java developer. Is it applicable for me?

[@Javatechie]

Yes buddy

[@devarajk6858]

@@Javatechie thanks 🙏 brother and is this enough or is there a continuation videos?

[@ravimane5508]

I really appreciate your videos. Your lectures are useful for experienced candidates. They are explained very deeply and well. Please add more videos. There are multiple people who have channels on KZbin, but yours stands out. You will be the next Javabrains

[@Javatechie]

Thank you so much for appreciating it buddy 🤗. Keep learning 👍

[@orangefield2308]

great video ! it would be helpful if these videos have time or question markers, to get to certain clips, or at least write the questions in the description, awesome channel@@Javatechie

[@patnalajahnavi1680]

String is threadsafe right as it's immutable but the slide shows it's not threadsafe 55:08

[@Javatechie]

Yes agree it's my mistake

[@harishgupta1392]

God of Java. Wish I had this in previous month before my Mastercard interview, I would definitely cracked it.

[@Javatechie]

No problem it happens i wish good luck for your upcoming interview

[@faixan13]

Such an awesome content and perfect timing. I was about to revise all the java basic to advance concept and here you go with the comprehensive and nice explanation of each n every concept. 🎉🎉

[@SagarBisen-kt8ex]

Definitely a must watch video, thanks a lot.

[@Coders_World]

2:03:45 does Hashmap Internally uses Array of LinkedList ?

[@Javatechie]

It’s linked list

[@Coders_World]

I mean those 16 memory buckets is Array ? Or Different DS ?

[@Javatechie]

@@Coders_World each bucket 🪣 point to a singley linked list

[@Kashi_nivashi]

55:34 - As strings are immutable, It is Thread safe. In the comparison table, String is mentioned as Not Thread Safe. Please correct me if I am wrong.

[@Javatechie]

You are correct and it's my mistake.

[@Kashi_nivashi]

@@Javatechie Thanks. Overall, This playlist is amazing. Even with 5 years of exp in java, such videos are needed to brush-up. Thanks a lot.

[@naleenyadav]

Boss is Back.

[@pavanik6863]

Because of break i don't have confidence but after watching this vedio slowly recovering 😊,thank you so much Basanth .

[@saranthoughts9826]

30:38 Compile time exceptions is compiler forcing to developer to handle the exceptions so its called compile time exceptions.

[@Javatechie]

Yes exactly

[@vishnuvardhan632]

This is very much needed video. Thankyou very much sir!!

[@trainlikeafighter9056]

Thank you RockStar for the Amezing video. You are explaining all the concepts in very simple way and they are really understandable. Your videos are really helping lot of people to clear the interviews. Thanks once again. Keep helping us. 🥰😀

[@Javatechie]

Thank you for appreciating my work buddy

[@satyabatigoswami1735]

I am 7 years experienced and find your videos very very useful. Your videos are really cutting edge. Please create some videos on latest features added in new releases of java after version 8. That will really help

[@Javatechie]

Sure buddy will do that

[@gs8589]

56:00 Immutable objects are by default thread-safe

[@subba18]

String is Thread-safe inherently.. In your picture it says not thread-safe @55:29

[@fiorini_mochachino]

Yup, was about to write that but you beat me to it. By 10 months... 😊

[@Madhav-p5q]

Hi Sir, Any plans to do the videos on any cloud like Azure, AWS or GCP.

[@punyabikash3624]

After long time happy to see sir❤

[@kraw-vo4oy]

really helpful and in depth :)

[@rashmi-l5t]

Hi basant... I had an interview today and your videos helped me a lot ..thank you so much ❤❤🙏

[@kamleshpatil1959]

Thank you for covering most of the topics...

[@KapilSoni-e5m]

No words to thank you sir.!! 🙏

[@DheerajReddy-p6u]

Thank you so much for this content before interview, i go though this video mostly 90% are the same questions great work

[@pawandeep8881]

Sir Thanks for the video ,in concurrent hash map what will happen when same bucket locked and it is trying to add the data in the same bucket ?

[@Harithakoritala]

Hi Sir i really like the way you get into the topic in depth, can you please make videos on Data Structures with Java now every company is expecting to know in deep about this topic. I live in USA and this is one more nice video from you.. i generally wont write reviews for any videos but after watching yours couldn't able stop myself appreciating your hard work.. Keep up the great work Sir..

[@splatthe]

Very helpful, thank you sir

[@VivekSharma-zb6no]

Strings are safe for multithreading, in your video at 55:45, it is shown that they are not thread safe, please correct it

[@nithya6361]

Can you explain why did you mentioned string is not thread safe?

[@saumyajoshi-ym2os]

Sir how many weeks/months it takes to master java8 and array/string questions to clear written test of service based companies

[@Javatechie]

One or 2 weeks is enough, i have a few questions already shared in the group just have a look in my channel

[@RockyRani-c2j]

Great Tutorial thanks Java Techie

[@Jeetu_24]

String is a thread...right but in screen(55:16 mnts) it is sowing not thread safe ?

[@Javatechie]

My bad it was my mistake

[@shantohossain1372]

55:59 isn't string is also thread safe? on the slide u r showing string is not thread safe!

[@Javatechie]

It’s my mistake buddy please ignore

[@mayankmanral4894]

Most informative practical video of core java interviews

[@rashmi-l5t]

Hi basant .. You explain in a very simple way which is easy to understand 🤩 Also I want to strengthen my java fundamentals..so is there any particular source from where I can learn it?

[@VaibhavYaramwar-rc7kl]

I think using ListIterator as well , We can able to modify List Object while iterating it as well. But only catch with ListIterator, Origin List should be created like List listObj = new ArrayList(). Meaning Origine List should not be fixed size List. For Example, For below mentioned Example, We will get java.lang.UnsupportedOperationException public class FailSafeIterationDemo { public static void main(String[] args) { List list = Arrays.asList("1","2"); ListIterator listIterator = list.listIterator(); while (listIterator.hasNext()) { String element = (String) listIterator.next(); listIterator.add("Z"); System.out.println(element); } System.out.println(list); } } But for another similar example, Mentioned as below , It will run perfectly fine without any Exception. public class FailSafeIterationDemo { public static void main(String[] args) { List list = new ArrayList(); list.add("1"); list.add("2"); ListIterator listIterator = list.listIterator(); while (listIterator.hasNext()) { String element = (String) listIterator.next(); listIterator.add("Z"); System.out.println(element); } System.out.println(list); } }

[@biswajitsaha6773]

Hi Basant, where is the link of github repo? i cant find it in description, could you please share it?

[@Javatechie]

I might have missed the update . will update and notify

[@biswajitsaha6773]

@@Javatechie Thank you Sir. Your contents are very helpful

[@hariprasad1727]

In Immutable class I tried for PhoneNumbers List.of("1234", "4567"); (or) Arrays.asList("1234", "4567"); also it's not allowed to modify. Thank You @Basant

[@rohanchowdary8511]

these are the best interview questions on java

[@Vithal_Nivargi]

Waw, awaited video. Thank you so much 🙏❤

[@gauravtiwari9263]

what do you mean by HashMap applies lock on entire. There is no lock as it is not thread-safe. You mean a syncronized map creation form this, for example from collections.synchronizedXXX or Sync version aka HashTable

[@rashmiranjanswain601]

It's incredible.Loved your videos.Please implement Fusion auth in Spring Boot.

[@Javatechie]

Not aware about fusion auth will definitely check and update

[@kumargagare6154]

What a timing man! This will really help me i. Preparation, thanks! Your content is very deep and practical!!

[@jagrutipatil1020]

As usual the bestest content we can found here☺️

[@d4devotion]

You earned my subscription because of this video.

[@sreerekhamenon1164]

Excellent content, thanks for providing them. Really helpful for interview preparation 🙂

[@niveditamirjikar409]

Why can't we provide constructor for abstraction? Only by creating objects we can call getter and setter methods of item class why is this best approach?

[@AdityaSharma-tt7yg]

You are a gem , Sir . Hope to meet you .

[@mericet39]

If you've been developing in Java so many years, it is possible to know all of this and still flunk the interview questions. For example, I was wondering "Pillar of oops? WTF does THAT mean?" Then when you started to explain, I realised I knew all those concepts but just not the label "pillar of oops"

[@Javatechie]

Pillars of oops or key component of oops this kind of word usually interviewer used

[@udayagiriveeru1366]

Thanks a lot... I really appreciate your videos. Your lectures are useful for experienced candidates. Can help to share the questions PPT that would be very helpful.

[@ashimasingh5031]

Amazing tutorial

[@farhaankazi7134]

My Finding for overriding. /* * 1. You can replace return type of super method with sub-type of returned type. * * 2. Exception hierarchy: Exception Declaration are of overriding can have sub type or same time * * 3. Method parameter of overriding should be same type even sub types are not allowed. * * 4. You can omit the exception declaration in overriding method but it is not allowed * define different or super type for exception area of method header. * * 5. You cannot override the static or private method. If you attempt override static method * then it is called overer-hiding. The scope of the private method is limited to the class * where you define it is not available to any of sub-class hence we you attempt to override * this super class private method in sub class, then subclass consider it's own new method * there is no relation between these duplicate method definition. * * 6. Overriding method in subclass access specifier can be broader or same. Meaning if Super class * Overridden method has protected access specifier then sub-class overriding method * can have public specifier but cannot have private or default one. * * 7. Super class method which has default access specifier cannot be overriden by the subclasses in * Other package. Only subclass in same or sub package of super class can inherit it and can override * it. * * 8. You can use modifier in parameter list of overriding method even if those modifier is not used in * the parameter list of overridden method in super class * * 9. Order, Type and count of parameter list of overriding method in super class must strictly match with * parameter list of overridden method in sub class. */

[@mkSlayer9]

Can you also create a multithreading Interview QnA video ? Please. Also eagerly waiting for Spring Boot Part 7. Thank you so much for all your efforts !

[@norulshahlamjohn1140]

giving an answer by coding it makes understanding better and deeply engrained by just watching. you sir are a diamond. but when i saw the boilerplate codes in your pojo i know you are an old-fashioned guy lol. also, comparator() is considered 'deprecated' since we are using streams api. do people still use that?

[@Javatechie]

First of all thank you for your words and BTW I am not an old fashion guy 🤪. It's just interview questions where they will check your basic understanding that's why I have explained the comparator

[@yoshitamahajan353]

Can u also create aws related questions in similar way that would be very helful....

[@nikitaparmar1190]

Your technique is excellent and easy to understand. Can you create a series on design patterns in Java? It is an important topic for practice and interviews. I couldn't find any design pattern series on your channel.

[@Javatechie]

Sure will plan it

[@divyavegoti4609]

Please make interview series on microservices and thank you for all the great work🎉

[@Javatechie]

Yes buddy as part of spring boot interview Q&A only i will continue.

[@gautamfitnesslook295]

Thank you sir it's very helpful for beginner to experience person.

[@hanumanthram6754]

Could you also please create a video on ThreadLocal?

[@Suraj-dj5rk]

Really very helpful bhaii.. thank you so much❤

[@vishwaranjansingh6111]

Simple I would say superb explanation

[@chanduyagnesh5501]

when catch block is not executing when exception is raised and return 3 only why sir

[@sachinchougule9117]

It's Very helpful content

[@VedantDhage-vb8kt]

Video is really very useful..do anyone having this pdf for quick revision?

[@test-nature]

is there PDF available ?

[@Javatechie]

No pdf , even didn't remember whether it's there in my machine or not

[@purushothamachowdary6340]

what is the difference between the below 2 statements? both are printing same results.. System.out.println(s1.intern().hashCode() == s2.hashCode()); System.out.println(s1.hashCode() == s2.hashCode());

[@Javatechie]

Could you please first try to understand what the intern method does ?

[@itsnarahari]

@Java Techie Why can't you create questions for unit testing

[@kralns2868]

Wonderful explained

[@patrisrikanth12]

Such a wonderful content....

[@karthikeyanrm3446]

Awesome video.. please continue this java questions series as well as Spring-Microservices questions series. Is it possible to give questions in the description?

[@Javatechie]

Yes definitely i can but i was thinking to share these questions as a separate medium Blog

[@karthikeyanrm3446]

@@Javatechie thank you so much Basant. Please share the link because it will be easy to revise - both java and spring boot - Microservices questions. Kindly do complex Microservices scenario based questions.

[@nitinbhattacharyya8784]

Hey I have a question. How do you stay updated with various changes in SpringBoot over the years?For example in Spring Security we used to use WebSecurityConfigurerAdapter but now we just create a SecurityFilterChain bean. How do do you learn about these changes and then update your knowledge?

[@Javatechie]

I do follow different blogs and spring official page in telegram and other official resources to keep myself updated

[@jasminpadaniya8199]

Hi@@Javatechie, Can you please share links to these resources like telegram channels and blogs? Thanks in advance

[@Javatechie]

Telegram: t.me/SpringFrameworkZone Blogs do follow to different blogs in medium or just search over Google and follow other resources

[@krushnnabaviskar4131]

Thanks for detailed expalnation.

[@hariprasad1727]

String s1 = "Hello"; s1.concat(" World!"); It will print "Hello" if we assign s1 = s1.concat(" World!"); ---> Hello World! similarly s1 = s1 + " World!"; it will print ---> Hello World! untill we assign variable after concatenarion it will not concatenate.

[@kukuusah]

Please make a Vedio on SQL interview questions and answers for 2 years of experience

[@shariefrana]

Great videos and excellent presentation, it would be great if the video is split into parts based on questions, so that viewers can skip to the question to which they don't know the answer.

[@Javatechie]

People suggest for long videos buddy that's why I uploaded it

[@orangefield2308]

he's talking about splicing in clickable segments, so you can click a certain topic in the video time mark, overall the video is good thanks@@Javatechie

[@Javatechie]

@@orangefield2308 yeah thanks buddy 👍 got it sure i will add timestamps so that it will be segment wise clickable

[@mhpgmadha343]

Please upload spring, Hibernate and spring boot also 🙏

[@harshadathakare5563]

Excellent

[@Srikanthb4040]

Hi basant, if possible can your please make notes of it and please share ppt

[@rohitd9952]

Can you please make a video on role based authentication and authorisation and also jwt authentication and authorisation using spring boot and spring security 6 latest update

[@Javatechie]

Please be updated with channel your requested video already available kzbin.info/www/bejne/hJSvpX-QpqyoaK8

[@rohitd9952]

In role based authentication and authorisation I found some are deprecated like csrf(), AuthorizeHttpRequests(),and(),formLogin() in current update it is showing me for removal

[@rohitd9952]

I filtered KZbin according to this month on role based authentication and authorisation i didn't find appropriate video on it, kindly help me

[@Javatechie]

Here is the update change log kzbin.info/www/bejne/j5_Lk4eieKiJgsU

[@Pradeep-jh7jc]

Appreciate this man's efforts. I regularly follow his videos and he makes everything so simple and easy to understand. Thankyou JavaTechie. :D

[@abhishekgwal878]

At 55:05 Correction - String is thread safe.

[@Javatechie]

Mu bad buddy 😞

[@shubhampatidar6116]

Again great video , Thanks a lot

[@Abu-k4t2n]

Yes Basant. Cover With Scenario all topic

[@parwezalam7242]

Guys I couldn't able to find this code on github anyone please help me

[@KD-fc3vq]

Hi Sir, Please create video on java LTS latest features as well. Since lot of interviewers expect nowadays.

[@SandhyaMadire]

One thing to notice here, as string having immutability nature makes it Thread safe.

[@harshsrivastav2197]

Strings are thread safe, right?

[@Javatechie]

Yes you are correct please ignore my word

[@giridharreddy4278]

Are these questions enough for core Java in interviews

[@JP-programming]

Great job 👏

[@piyushsharma5947]

Thanks alot for the wonderful video! I know you have provided alot of effor t in making this video. It is really helpful. Can I request for a separate pdf notes as well ? It will help us in going through just before an interview. BTW keep bringing more such videos and with notes if possible :)

[@bhargavi4557]

I have asked a question to get employee namesand age>30 ,emp id between 50 and 70 I was able to answer first two conditions. Can you help me witg empid between 50and 70 elist. Stream().map( Employee::getnames).filter(x->x.getAge>30) Can you help with id condition

[@praticksharma4820]

First filter it then map it filter (x->x.salary>30 && x.salaryy.name)

[@bhargavi4557]

@@praticksharma4820 condition between 50 and 70 is for emp ida

[@bhargavi4557]

@@praticksharma4820 How to find the emi ids from 50 to 100 I have tried Elist.stream(). filter (x->x getId()>50 && getId()>100).forEach(s->syso(s)); Its not working can you help me

[@gopisambasivarao5282]

Hi Basant, waiting for your new videous.Last week we have not seen any new video. Hope this week.😊Appreciate your efforts

[@Javatechie]

Hello buddy thanks for your interest 😊. Actually I was on vacation and returned today so hopefully next weekend i will start uploading content

[@gopisambasivarao5282]

Thanks Basant. Appreciate your time. God bless you. 🙂👍🙏

[@uvanana.]

Is your playlist is enough for Capgemini interview sir

[@Javatechie]

Yes it's more than enough for any company irrespective of service or product base only for core Java Q&A

[@uvanana.]

@@Javatechie Thank you sir , and for Java interview coding do you have a playlist

[@Javatechie]

Yes please filter with keyword " programming " you will get a couple of videos in my channel

[@hkk4782]

please add on concurrency interview questions in java

[@TheTravellerVlogs99]

One more- We can overload static method. Right.

[@Javatechie]

Yes we can

[@johncater7390]

String is thread safe. time-55.17

[@SaurabhKumar-dj5vq]

Sir try block execute like if else

[@Javatechie]

No purpose is completely different

[@SaurabhKumar-dj5vq]

Ok sir