How HashMap Internally Works in Java With Animation | Popular Java Interview QA | Java Techie

This tutorial we will explain you How hash map internally works in java
#javatechie #CoreJava #InterviewQA
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[@NamChics]

I have seen many videos on this topic but no one explained this topic as simpler and easy as you explained...thank you so much bhagwaan apki har muraad puri kare

[@rohitkhandelwal313]

I saw more than 50 videos on hashing , but this was the one which made me actually understand, thankyou sir.

[@Javatechie]

Thanks Rohit. Keep learning 😃

[@PIYUSH-lz1zq]

bro , if there kar 2 null key then second value will be placed in ??

[@rohitkhandelwal313]

@@PIYUSH-lz1zq I think 0th bucket

[@rohitkhandelwal313]

@@Javatechie am I right?

[@Javatechie]

Yes correct

[@poojababar8746]

Sidhi bat no bakwas vala explanation, straight, simple , good work sir

[@subhamsharma8268]

That is a very simplified and a splendid explaination of hashmap. Thank you so much sir.❤

[@priyankashaw1238]

Your explanation is to the point and very clear. Request you to also add how hashmap retrieval works when there is more than 1 key in the same bucket.

[@Javatechie]

Okay i will buddy

[@gandamraviteja7019]

Great thank you so much just less than 10 mins you cleared lot of things
even thanks feels tiny for ur work

[@manamohansamal1040]

Brother your explanation helps to easily understand the topic. ❤️❤️ One request if you can make a video one interview questions with different types of url mapping to the dispatcher servlet like /,/*,/** etc . It will be very helpful 🙏🙏

[@Javatechie]

Okay I will do that. This is kind of URL patterns

[@girishrp9339]

In youtube have more than 1000+ videos same question but your video is very easy to understand.

[@Javatechie]

Thanks buddy 😊

[@AayushGore-]

When i thought of this q i thought of receiving answer from java techie. I search on RUclips and first video your name came 😂

[@maankhurana5814]

Awesome watched 10 more videos on youtube before this .... not able tp understand concept... but u made it very simple ... Thanks alot

[@acchutdevkule7841]

You are one of the underrated tech youtuber ...

[@Javatechie]

Thanks buddy 🙂 for your word . Will hope to grow soon .

[@charangowda384]

Bro I have seen a lot of videos , but this is by far the best explanation video i have seen on youtube clean, simple and clear.

[@Javatechie]

Thanks buddy 😊. Glad to hear this ☺️

[@PraveenKumarpksksit]

Thankyou for so much detailed and simplified way of teaching HashMap. It is really helpful for anyone who wants to either learn fresh or just wants to revise again. Really Appreciate !!

[@pateldharmesh1361]

Bhai your tutorial clears all doubts most of the time

[@prajwalbandekar3557]

The BEST easy explanation out there, Thank you Sir 🤝

[@sameerkadgaye2048]

Very clear explanation thank you sir

[@muralitreddy]

Simple and neat explain

[@priyay]

Simple and clear thankyou

[@sergiogb]

Thanks, good an easy to understand

[@subramanianchenniappan4059]

thanks bro. useful for interviews. i am a java backend restful API project tech lead. will apply for job

[@Nikhil-jf7lv]

Welcome to java tikki ❤

[@ranjithkumarravichandiran8983]

Thank you so much for clear explanation.👏👏

[@raghugupta8959]

i understand very clear,thanks for explaining neatly🙂🙂

[@forouzannaderi-vw3sp]

great explanation thank you so much 😍👏

[@kirane5911]

Very good explanation

[@rajraj8065]

Awesome explained, keep making such a good vedio .

[@pirate1239]

best explanation. easy one

[@FacundoMartín-z2r]

Thank you so much for this explanation! It's really clear with the examples you did :D

[@pranavjog172]

Hi, Could you please make a video on HashMap internal working in Java 8 or new addition in Java8 for HashMap?

[@chetanbhandari3033]

Awesome explanation waiting more interviews questions videos

[@amscoder5262]

Simply awesome explanation brother 👌👌👌

[@Javatechie]

Thanks brother 🤗

[@vinaypandey4752]

Awesome explination

[@vivekkumar-iy7zk]

Thanks you explained so well

[@NamChics]

I am subscribing your channel just because of this video

[@Javatechie]

Keep learning 👍 I believe you like other videos as well

[@nagireddy1507]

very clear explanation... Thank you

[@devopsshiv3842]

Yes, i got the internal hashing collision part

[@tolgacelikart]

great explanation , and thanks for sharıng. Just little feedback maybe :) same pronunciation was distracting me time to time on focusing, such as zero (sounds g..), hash (has), etc.
also some of saying 'ok , fine, right, after explaning something etc ' .

[@raghavagarwal6545]

Simple awesome explanation👍

[@maheshrevaskar7658]

Thanks Basant! Video on working on ConcurrentHashMap will be helpful. Saw many videos, but still its not clear.

[@Javatechie]

Sure i will do that

[@natureParadise777]

Like your videos, you explain the topic in very beautiful way, please make more videos on the interview questions...

[@Javatechie]

Thanks buddy 😊

[@bhargavarajuthirumalasetty]

this is simplified. thank ..

[@zuggrr]

thank you soooo muchh ! you are the best

[@ranachan5555]

I am not finding you concurrent Hashmap in your list, Please send the link

[@naveenkumardasari]

It would be more helpful, if you explained about retrieving elements from hashmap.

[@Javatechie]

Will do another video

[@raajaakowsalya2711]

Hey!!! Seriously well explained 😀❤️✨✨

[@AbhijitDixit-ki1oo]

Thank you so much sir 🙏

[@supun_sandaruwan]

All In one video Thank you sir 💖

[@rohitchanda8461]

I love this channel's content

[@Javatechie]

Thanks buddy but BTW what is

[@rohitchanda8461]

@@Javatechie haha, no, it’s ❤️ thanks for the content!

[@praveens2272]

Nice explanation

[@Javatechie]

Thanks 😊

[@ramyasruthi5372]

Thank you!!! Very detailed

[@Satenc0]

Very good explanation sir overall, but I have one little question about the hash collision, at min 5:38 you say that it first uses double equals (==) to check if they have the same hashcode, which means to check if they have the same reference right, if they result to have the same hashcode then it will just replace, but if they dont, then it will check if they have the same value (content) with .equals() method (key1.equals(key2)) right, if it is true then replace, if not then add the next node, is this well understood? please correct me if not

[@Javatechie]

Yes your understanding is correct

[@MaheshAnand1995]

Should have been more helpful if you explained the get process as well. Thank you

[@RaviShankar-xy6zh]

Bro you always bring great and interesting videos in eloquent way.

[@Javatechie]

Thanks buddy 😊

[@selvapandymoorthy4173]

Great explanation

[@mohammedajazquadri7869]

brilliant explanation

[@ShivaKumarSatakuri]

Can you explain data retrieval for the same example?

[@basitali9651]

Thanks for this info..God job sir

[@Javatechie]

Thanks buddy

[@murugeshk14]

Thank u it's was short and simple 🙌

[@mintybreez]

Very well explained 👏

[@VishalSharma-rn7mt]

Awesome

[@vipintekade6400]

Lovely .

[@pravin.a.mahajan]

Hi Basant, Recently I got one question from interview that, will it create bucket of 16 when you create map instance? I did debug the code and found that it creates bucket when you first element into map. your explaination at 1:00

[@Javatechie]

That's correct but will cross validate and update you

[@pradeepnayak1988]

Great Work Basant. Keep Growing.

[@Javatechie]

Thanks buddy

[@scoobydooby4672]

Nice thanks

[@simplyarranged]

Thanks sir🎉

[@TanishKumar-uz4wk]

Great !!!

[@adityavyas6603]

Very nice explanation Basant... One question if we change the content of employee object after adding as key in map then what happened..
And in case of immutable employee class what is the behavior of map.
Thanks in advance..

[@Javatechie]

If you will do get (key) you will get NPE

[@sudheergundubogula]

Thank you so much ❤️

[@pratishrutipanda6461]

You nailed it 🔥🔥🔥

[@Javatechie]

Thanks Pratishruti 🙂

[@sivarama8116]

Tx sir

[@learnprogramming6930]

Thank you

[@PoudelP]

5:03
Correct me if I am wrong but if (e1,"Dev") & (e3,"UI") both coincidentally have the same hash value, then wouldn't the hash value for second linked list at 6 be 1011, just like the linked list above it?

[@ankush_in_sync5998]

Thanks

[@soumyaranjan6196]

Awesome explanation bro 😊

[@Javatechie]

Thanks Soumya 😊

[@Akhilesh_Reddy]

Good one Basant.

[@Javatechie]

Thanks buddy 😊

[@priyanaik4099]

Awesome explanation. Thank you. Can you make video for springboot?

[@mohammedajazquadri7869]

Sir please make videos on design patterns it is mostly Asking now a days in interview

[@Javatechie]

Okay buddy I will

[@kishorep5572]

Guys, what is the out of it?
Map map = new HashMap();
map.put("a", "B");
map.put("a", "C");
map.put(null, "C");
map.put(null, "C");
map.put(null, "A");
System.out.println(map);

[@Javatechie]

Output will be a, C and null , A

[@vasuimandi5535]

Bro, can you make a video on mock interviews or can you make video on all common interview questions in Java, So that will be helpful to those who wants to change company....

[@Javatechie]

Hi vasu , please check below link it's already there for core java
ruclips.net/video/fFnuer3AD8Q/видео.html

[@Javatechie]

Part 2 : ruclips.net/video/GO67C7V-IbQ/видео.html

[@initToLearn]

@@Javatechie Thanks

[@rohitsharma-xt8qe]

5:38 here you said Map first internally used == operator to check the reference and if it is different then it will use equals method. But in the last diagram you haven't showed this ?

[@snehakarosiya2618]

thank you so muchh !!

[@mlevidigeri]

You’re videos very helpful. Can you please do a video on java events

[@Javatechie]

Java or spring events ?

[@mlevidigeri]

@@Javatechie spring events

[@Javatechie]

Okay I will do that

[@vinaypandey4752]

Sir, what will happen, if a duplicate value is given to add, will it will check for duplicate value? Suppose if we have same value in index 1 and same value is send again to add on index 3, it will add or it will not add it?

[@sivakrishna2544]

Hi bro can you make one vidow difference between 1.7 and 1.8 difference in HashMap internal architecture

[@Javatechie]

Sure will do that

[@sivakrishna2544]

Thanks a lot bro❤

[@jagadeeshbelagallu5243]

If put Method find same content what will happen? is it throw error or ignoring to store the content into that object?
If e1.equals(e3 is it override e3 content?

[@NSINGHK]

It doesn't have linkedlist, it uses resizable array thsts why it fetch in O(1) time, if its linkedList it will fetch map.get(key) in O(n) which is wrong

[@Javatechie]

Hello buddy,
It depends on many things. It's usually O(1), with a decent hash which itself is constant time... but you could have a hash which takes a long time to compute, and if there are multiple items in the hash map which return the same hash code, get will have to iterate over them calling equals on each of them to find a match.
In the worst case, a HashMap has an O(n) lookup due to walking through all entries in the same hash bucket (e.g. if they all have the same hash code). Fortunately, that worst case scenario doesn't come up very often in real life, in my experience. So no, O(1) certainly isn't guaranteed - but it's usually what you should assume when considering which algorithms and data structures to use.
In JDK 8, HashMap has been tweaked so that if keys can be compared for ordering, then any densely-populated bucket is implemented as a tree, so that even if there are lots of entries with the same hash code, the complexity is O(log n). That can cause issues if you have a key type where equality and ordering are different, of course.
And yes, if you don't have enough memory for the hash map, you'll be in trouble... but that's going to be true whatever data structure you use.

[@1stnamelastname24]

If "key" is null then it will placed at 0th bucket then what if "Value" is also null ?

[@shubhammahindru3563]

Hi,
why is the size is still one ?
Car car = new Car("Seletos",2020);
Map carMap = new HashMap();
carMap.put(car,"1");
carMap.put(car,"2");
System.out.println(carMap.size());
In car class, I have the following implementation of the equals and hashcode ?
@Override
public boolean equals(Object o) {
return false;
}
@Override
public int hashCode() {
return 1;
}
car.equals(car) will give it false and it should have added it as the next node but its giving the size as 1 and only node its adding ?
I am confused in this please help, if u got some time.
is it ? if the keys are same then it first checks == if not then only it goes for equals comparison ?

[@Javatechie]

In both the case hashcode will be 1 only right which is again duplicate

[@shubhammahindru3563]

@@Javatechie Yes 1 but it should go and check for equals method which would return false(because of overridden method) and would add the value as next node ?
So it means for duplicate keys equals method is also not checked it simply replaces the value ?

[@Hamza-Shreef]

5:47
I think if it finds the same reference or the same value it will throw an exception right ?
and there is no replacement happening there.

[@Javatechie]

No it won't throw any exception just debug and see

[@Hamza-Shreef]

@@Javatechie Yes i mean i'm sorry i'm a c# developer and we have a dictionary instead of hash map but i thought they were the same .
thank you for pointing that out to me ❤❤

[@PIYUSH-lz1zq]

bro , if there kar 2 null key then second value will be placed in ??

[@codecompany7114]

ok good,
but what is the importance of Next then?

[@PIYUSH-lz1zq]

bro , if there kar 2 null key then second value will be placed in ??

[@Javatechie]

Yes

[@murugeshk14]

If u first put(null, 8); its stored in the 0 th index and if again u try to put(null, 9);
Then that first entry get replaced by this new entry in the same 0th index as in hashmap duplicate keys are not allowed, if u try to add entry with same key it's gets override

[@zsoltgeza]

You should create captions, because they cannot be created automatically under Your video

[@Javatechie]

Didn't get you buddy

[@sivabalarasup7556]

I think, he is referring to Subtitles. You could add subtitles.

[@zsoltgeza]

@@sivabalarasup7556 thats right

[@itsnarahari]

Bro in which company ur working on ?

[@Javatechie]

Walmart buddy

[@aloktiwari4188]

Hi sir please make video with Java 17 example

[@saudsiddiqui5698]

How to access the entry having null key? like map.get("?");

[@10000Deepak]

it does not matches the content itself, unless you have overriden equals method, you are mistaken here

[@leandromarcelo2340]

could you activate the subtitles? pls

[@Javatechie]

Please click on CC while watching video. I already enabled it buddy 😊

[@MadhusudhanNalla]

what if, the equals method returns true? time:4:45

[@sproutboot]

That means the case just updates the value

[@RN-jo8zt]

what if two duplicatre was there in put() .you missed this VVVV.important concept

[@vandanac2244]

If key is duplicate it will be overriden

[@Javatechie]

Yes

[@Regnarr39]

Ok? Ok