For anyone confused about how the index value is calculated: the “&” operator is a “bitwise AND” operator. When it is used, both its operands (the numbers before and after the operator) are converted to binary, and a bitwise “and” is performed on each pair of matching place values in both binary numbers. This results in a new binary number. For example: 12 & 5 = 4, since 1100 & 0101 = 0100 And also 2306996 & 15 = 4, since 1000110011001110110100 & 0000000000000000001111 = 0000000000000000000100
I think I will add one more point at 7:50, When you call put() for the element having the same index or hashcode() it calls equals() method as well to compare the key. If it's same then it will overwrite the previous element and if not then append to the next node. This part is very important because once I was asked what will happen if you only implement hashcode() and not equals() or vice versa.
@@ArkAngelHFB no, it doesn't make sense to overwrite the key, because its already in the array. Instead, the value is overwritten, because the hashmap doesn't tolerate duplicates. This can be also tricky when we deal with children nodes, for instance with one-to-many relationship. Sometimes one's better of to override children's hashcode() based on their class only, so that all children (objects of the same class) have the same hash code.
I'd like to add a point to the wonderful explanation of HashMap implementation When HashMap reaches its threshold limit of .75 or 75% it re-size by creating a new array of double the previous size HashMap, and then start putting every old element into that new bucket array and this is called rehashing and it also applies hash function to find new bucket location.
we need to do it so that get and put operations can be done in O(1). if we dont do it, the size of linked lists would keep on increasing and would eventually increase the cost of operations.
This HAS to be one of the finest tutorials I have ever seen. The use of the animation was extremely well thought out and makes the subject so clear even a non-developer should understand it! Very well done! Thanks for your efforts Ranjith.
Right on my dude. I've been struggling with one specific piece of the implementation (what we do with the hash code), but this video explains it perfectly. Thank you!!
my friend, I wish i saw this 3 days ago.... I didnt learn anything new because I have been studying hashMaps pretty aggressively the last 3 days, but my life would have been A BILLION TIMES BETTER if i found your video first. Beautifully detailed and easy to understand! TO BEGINNERS, THIS IS THE BEST INTRO TO HASHMAP VIDEO ON UA-cam!
Great explanation. The only point I feel missed was when two keys have the same hashcode the Node actually overrides the original nodes and doesn't get appended to the Linked list. Your run case could have included this scenario.
@@ranjithramachandran5928 Hi, Sir, I have a doubt, kindly explain plz. My "Eclipse IDE" showing two hash value for key "apple" (and for others key too), i.e, 93029210(index = 10) and 93030097(index = 1). According to formula it should be index=10, but it is placed at index= 1. Kindly, explain why we get two hash value for each key, and why its index is 1 and not 10. 🙏🙏🙏
@@ranjithramachandran5928Hi sir Nice Explanation and I have a small doubt, could you please explain once,In MAP, If two Entries having same key and same hashcode?? HashMap map=new HashMap(); map.put("101","hdfc"); System.out.println(map.put("101","sbi")); //Returning value is = hdfc //After iterating Map, and getValue() method returning = sbi Could you please explain why it's print 'sbi'', How about hashcode and equals method work in this case????
Hi Ranjith, In the first put operation scores.put("KING",100). your index comes to 4. But according to index = hash % (n-1) it should be index = 2306996 % (16-1) this gives 11 and you calculated it as 4. However, if we put 'n' instead of 'n-1' we will get result as 4. So either the formula hash % (n-1) needs to be changed to hash % (n), if you are calculating indexes correctly or if the formula is already correct, your index must come out to be 11. need your comment on this. thanks
+Vincent Lal Wondering how you can calculate like that. Do it bitwise . 2306996=1000110011001110110100 , (n-1)=(16-1)=15= 1111 , 1000110011001110110100 AND 1111 = 0100 which in decimal is 4.
+Yogesh Bhat - hash(k) in real implementation is done to address "poorly" implemented hashcode methods in classes, that will cause a bucket(or index) loaded with too many nodes(or in older terms entries). It basically spreads higher bits of actual hashcode to lower order. This is done because the modulo operation produces different results only based on lower order btis.(in base 10, think of numbers at 'ones' position)
Ranjith, You have Awesome teaching skill. Without any doubt , This is the best explanation of Hashmap . I experienced the same ease of my understanding regarding your garbage collection in Java explanation too. Cool.
During put operation, why did we need to compare the hashcode, only comparing the keys will work. Say for an instance two keys have a same hashcode, in that case comparing with hashcode takes you no where, you have to compare key. May be I am missing something, please correct me I am going somewhere wrong.
Splendid explanation with Animation. I have been using HashMap more than decade. Now, I got clarity how it works internally. Thanks for the commendable work!!!👏
Quite awesome..... presentation with nice crystal-clear language.....so nice....so much helpful.....I was so confused from last 4-5 years.....but today its remove all deadlocks of confusions and misunderstanding about hashmap's Internals......
Fantastic video, thanks a lot - very clear! It's nice to have the little inserted video of you as well, somehow it helps to improve focus throughout the video
Thanks Ranjith for tutorial. After referring to tutorial I visited the actual source code of Hashmap and now its pretty much clear about the functioning of put and get method and also about resizing of the table size when it reaches the threshold.
This is just crystal clear explanation!! The best explanation for hashMap!!! And thank you for the information about the updated hashMap in Java 8. That's so cooool and smart!!
Thank you very much for this wonderful piece of work. Now certainly I got an idea of how exactly Hashmap works internally.Gonna check the internal activities of put, get and hash in jdk 8 also. Keep the knowledge flowing. :)
For anyone confused about how the index value is calculated: the “&” operator is a “bitwise AND” operator.
When it is used, both its operands (the numbers before and after the operator) are converted to binary, and a bitwise “and” is performed on each pair of matching place values in both binary numbers. This results in a new binary number. For example:
12 & 5 = 4, since
1100 &
0101 =
0100
And also
2306996 & 15 = 4, since
1000110011001110110100 &
0000000000000000001111 =
0000000000000000000100
Thanks Rick
How to get the hash value
This is just wonderful
Thanks Rick
Thanks rick
I think I will add one more point at 7:50,
When you call put() for the element having the same index or hashcode() it calls equals() method as well to compare the key. If it's same then it will overwrite the previous element and if not then append to the next node.
This part is very important because once I was asked what will happen if you only implement hashcode() and not equals() or vice versa.
This point is very necessary to complete this good video.
Very good point, thanks
Would this mean that without the equals() method call, a HashMap could erroneously overwrite both Key and Value at the same time?
@@ArkAngelHFB no, it doesn't make sense to overwrite the key, because its already in the array. Instead, the value is overwritten, because the hashmap doesn't tolerate duplicates. This can be also tricky when we deal with children nodes, for instance with one-to-many relationship. Sometimes one's better of to override children's hashcode() based on their class only, so that all children (objects of the same class) have the same hash code.
@@dmitrikonnov922 But without the equals() call, wouldn't it just assume that since it shared the same hash, it WAS the same key and overwrite it?
This is the best tutorial I found for "How HashMap works"! Demo using animation is remarkable :)
I'd like to add a point to the wonderful explanation of HashMap implementation
When HashMap reaches its threshold limit of .75 or 75% it re-size by creating a new array of double the previous size HashMap, and then start putting every old element into that new bucket array and this is called rehashing and it also applies hash function to find new bucket location.
for any object the index will be 0 to (n-1) when we take mod of (n-1), then why we need to re-index or it re-sizes ???
we need to do it so that get and put operations can be done in O(1). if we dont do it, the size of linked lists would keep on increasing and would eventually increase the cost of operations.
It does not take double size but size equal to next power of 2.
You're implicitly stating that it's double ... as a previous power of 2 ( 2^4) is being multiplied by 2 .
this was important part... yet nit covered
This is probably the best explanation of Hashmap I've come across! Kudos to you!
People who has disliked, what are you guys expecting ? This is just perfect explanation!!
:) right
Best explanation. Perfect
This HAS to be one of the finest tutorials I have ever seen. The use of the animation was extremely well thought out and makes the subject so clear even a non-developer should understand it! Very well done! Thanks for your efforts Ranjith.
Right on my dude. I've been struggling with one specific piece of the implementation (what we do with the hash code), but this video explains it perfectly. Thank you!!
HashMap working animation + enhancements for HashMap in Java8 - check out! If you liked, please leave a comment!
+Ranjith ramachandran Really good! This is the best tutorial about "How HashMap works"!
Very Helpful video on HashMaps. I actually understood how Look up works. Thank you...
Sir,Please share how Hashcode made...!!!!
Very wonderful tutorial....Can you please also explain in animation How ConcurrentHashMap and ConcurrentLinkedQueue works?
Thank you
my friend, I wish i saw this 3 days ago....
I didnt learn anything new because I have been studying hashMaps pretty aggressively the last 3 days, but my life would have been A BILLION TIMES BETTER if i found your video first. Beautifully detailed and easy to understand!
TO BEGINNERS, THIS IS THE BEST INTRO TO HASHMAP VIDEO ON UA-cam!
This is the best explanation available in youtube for Hashmap...!!
Holy shit I was confused about hash tables for so long and this video simplified in such a nice way.
Excellent job @Ranjith ramachandran! Keep doing it!
I was looking for a good explanation for a long time, and I found today. Thanks, Ranjith.
It's really sad that you aren't posting videos anymore. you have such great talent in teaching and you were a valuable resource on youtube.
Great explanation. The only point I feel missed was when two keys have the same hashcode the Node actually overrides the original nodes and doesn't get appended to the Linked list. Your run case could have included this scenario.
Good one brother
both hashcode() and equals()
I learned a lot about Hashmap from this video. Thanks a lot Ranjith, you have did a great job. :)
Great explanation about hashing and collisions...
HashMaps finally demystified. Thank you very much
This is the best video that I have seen by now, however its sad that you have stopped posting now
This is an in-depth very well explained video! Thanks a lot!
Thanks!
@@ranjithramachandran5928 Hi, Sir, I have a doubt, kindly explain plz.
My "Eclipse IDE" showing two hash value for key "apple" (and for others key too), i.e, 93029210(index = 10) and 93030097(index = 1). According to formula it should be index=10, but it is placed at index= 1.
Kindly, explain why we get two hash value for each key, and why its index is 1 and not 10. 🙏🙏🙏
@@ranjithramachandran5928Hi sir Nice Explanation and I have a small doubt,
could you please explain once,In MAP, If two Entries having same key and same hashcode??
HashMap map=new HashMap();
map.put("101","hdfc");
System.out.println(map.put("101","sbi"));
//Returning value is = hdfc
//After iterating Map, and getValue() method returning = sbi
Could you please explain why it's print 'sbi'',
How about hashcode and equals method work in this case????
Great explanation. If anybody want to know how HashMap internally works please watch this video once. Thanks for sharing such amazing video.
Amazing explaination and animation!! Love it.
Hey Ranjith
Very detailed and nicely animated work..It was easy to understand
Dude more videos please :) You are awesome :)
Excellent explanation with example of how hashmap put and get method works internally.
hands down this is the best video on how hashmap works internally. Thank you very much.
this is awesome explanation dude.. The best one for HashMap
😭
R
@@ginny5967 watzup buddy ?
@@ginny5967 wat made u cry
Correction: Whenever there is collision, the new entry should added as the head of linked list, not tail.
any references ?
p.next = newNode(hash, key, value, null);
Yes. Because the insertion will take O(1) time by inserting at head rather than tail.
Exceptional presentation of HashMap. Keep up the good work :)
This got to be the best explanation of Internal working of hasmap that I have ever seen.
Thanks..!
Hi Ranjith,
In the first put operation
scores.put("KING",100). your index comes to 4.
But according to index = hash % (n-1)
it should be index = 2306996 % (16-1)
this gives 11 and you calculated it as 4.
However, if we put 'n' instead of 'n-1' we will get result as 4.
So either the formula
hash % (n-1) needs to be changed to hash % (n), if you are calculating indexes correctly
or
if the formula is already correct, your index must come out to be 11.
need your comment on this. thanks
+Vincent Lal Please note the index is calculated as hash & (n-1) which is same as hash % n-1
it should be n only as the operation always outputs 0 to 15 which are indexes of the table 0 to 15.
+Vincent Lal Wondering how you can calculate like that. Do it bitwise . 2306996=1000110011001110110100 , (n-1)=(16-1)=15= 1111 , 1000110011001110110100 AND 1111 = 0100 which in decimal is 4.
How hash(k) is calculated? Can you please explain..
+Yogesh Bhat - hash(k) in real implementation is done to address "poorly" implemented hashcode methods in classes, that will cause a bucket(or index) loaded with too many nodes(or in older terms entries). It basically spreads higher bits of actual hashcode to lower order. This is done because the modulo operation produces different results only based on lower order btis.(in base 10, think of numbers at 'ones' position)
Really good explanation with the help of animation.
Ranjith, You have Awesome teaching skill. Without any doubt , This is the best explanation of Hashmap . I experienced the same ease of my understanding regarding your garbage collection in Java explanation too. Cool.
During put operation, why did we need to compare the hashcode, only comparing the keys will work. Say for an instance two keys have a same hashcode, in that case comparing with hashcode takes you no where, you have to compare key. May be I am missing something, please correct me I am going somewhere wrong.
keys are objects, you'll need to run .equals(). integers are much faster to compare via "&"
I had asked the same question. :-)
Good explanation, but can you remove the recording of yourself, frankly it is a little disturbing to watch your head tilt frequently.
true
true
yes its kind of disturbing ..
lol
well that's ungrateful
Splendid explanation with Animation. I have been using HashMap more than decade. Now, I got clarity how it works internally. Thanks for the commendable work!!!👏
Amazing approach!!
Thanks a lot worked like a charm!!!
Your face is in the way of the slides. lol
dude stop coming back and forth in to the screen. Its distracting
Excellent demonstration of HashMap implementation!!
Great and useful information with clear explanation and awesome animation. Thank you.
Simply perfect ! Awesome explanation
very lucid way to present the explanation, awesome, thanks alot.
Absolutely fantastic use of animation for presentation. understood in one shot. Thanks for taking the pain of wonderful preparation. excellent work!
This is the first explanation that has made sense to me! Its like an epiphany! Thank you!
Very good video! Thank you for your explanation.
Thanks man! I just learnt something from you! Please keep up the good work.
Very well explained, now i can easily visualize the Hashmap structure and the way how Key-Value stores.
Thanks a lot :)
liked, subscribed and i can never forget hashmap implementation for life time now.
Quite awesome..... presentation with nice crystal-clear language.....so nice....so much helpful.....I was so confused from last 4-5 years.....but today its remove all deadlocks of confusions and misunderstanding about hashmap's Internals......
I like when I can see the lecturer on the screen. Good explanation, this is what important in here
Nice video, very engaging and loaded. Kuddos
very well explained .. Thanks for sharing!
very well explained. Thanks for the video!!
so well explained!!! implementation details and the class heirarchy in just 15 minutes! You're a great teacher
Thank you very much for the work. Explanation is clear and animation is very good!
This is the best tutorial i've ever seen for understanding HashMap thanks a lot !
From Morocco
Amazing, thank you for this bro.
One of the best resource on HashMap. Really stunning !!!
Very nicely Explained..Kudos to you (Y)
Awesome!! Really enjoyed watching it so much! Thank you!
Very Nice explanations Sir thanks a lot... for sharing
Superb explanation Sir, keep it up and keep aspirants enhance their skills.
So helpful and explained in a very simple way
Nicely explained! Thanks, keep creating !!
Thank you!! Excellent video
Excellent. Thanks for posting.
Best explanation from all videos I looked on yt.
this is THE BEST EXPLANATION of HashMap...thanks
perfect video to learn how hashmap works in a very short time.
Very Good Explanation for Hashmap implementation..Thank you...
Wow, this is the best tutorial about itHashMap on UA-cam!
Best video i have ever found in you tube regarding implementation of hash map .Described it clearly
Recommended video
Simply explain how it happens well done
Great video, this is the best video Ive seen explainig how hashmap works, thanks!!!!
The animations help remember things.. Kudos...!! Thanks
Fantastic video, thanks a lot - very clear!
It's nice to have the little inserted video of you as well, somehow it helps to improve focus throughout the video
Nice presentation with animation. Thank you...
Thanks Ranjith for tutorial. After referring to tutorial I visited the actual source code of Hashmap and now its pretty much clear about the functioning of put and get method and also about resizing of the table size when it reaches the threshold.
I really like visual explanation, Appreciate you and thanks to share
Loved this explanation!! thank you
Use of animation really helps understand the concept.
Thank you so much sir 🙏
Too good!!! thanks for helping me to understand the internal hashmap work in java
Thank you Ranjith. Appreciate your efforts. This definitely going to make difference to learners... Great job!
This is just crystal clear explanation!! The best explanation for hashMap!!! And thank you for the information about the updated hashMap in Java 8. That's so cooool and smart!!
Best HashMap explanation and animation !
Thanks for the great explanation and great work!!
Best tutorial for understanding HashMap. Thanks a lot !
Thank you very much for this wonderful piece of work. Now certainly I got an idea of how exactly Hashmap works internally.Gonna check the internal activities of put, get and hash in jdk 8 also. Keep the knowledge flowing. :)
Thanks for sharing knowledge It helped me to understand.
Very well explanation of HashMap .
awesome explain about HashMap
Thanks a lot, i was really afraid and bit confused about this concept , finally I found this explanation and I'm really so happy.
This is excellent. Thanks Ranjith. Looking forward to hear more such tutorials from you.
Nice Presentation of the Map concepts!
Its always a good time while watching your precious and informative videos. Very good and easy to understand. Thanks alot
Good tutorial for hash map implementaion