#14 - linkedhashmap vs hashmap in Java || How LinkedHashMap works internally - Naveen AutomationLabs

In this video, I have explained what is LinkedHashMap in Java and How LinkedHashMap works internally.

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[arvindhr.a]

Great Video Naveen sir !
Can you add some comments or a short video for collision in linked hashmap ? I see many folks have requested for the same . if you could, it would be great :)

[SarangHoley]

Back to back new video 👍😊, thanks for the video Naveen

[Vishalfootball]

nice one Naveen, was waiting for this

[manikandan]

what an amazing explanation..Thank you sir

[rishibharadwaj]

Good to see a video on the internal implementation of a Collection class!
But, I have an interesting question here :
What if 2 keys have the same hashCode?
As per your logic, they will generate same index. How will you store 2 nodes under the same segment(bucket)?

I think instead of 2 pointers the nodes must have 3 pointers.
1. BackwardNode
2. ForwardNode
3. NextNode to point to a Node belonging to the same index(bucket).

Not sure if LinkedHashSet is implemented this way. Would like to hear from you.

[flivnrk]

Hello @Naveen,
I have one question regarding linkedHashMap, as per your explanation, does this mean 1 segment will have only one node created at any given point unlike HashMap where we could have maximum 8 nodes per segment?

[thanga]

Thanks for the explanation Naveen. You should've explained about Entry which is wrapper of Node.

HashMap.Node subclass for normal LinkedHashMap entries.

static class Entry<K, V> extends HashMap.Node<K, V> {
Entry<K, V> before, after;
Entry(int hash, K key, V value, Node<K, V> next) { super(hash, key, value, next);
}
}

[dikshabaluja]

You explain really well, Thank you so much

[sureshgarine]

Nice explanation Naveen! do we have any methods to retrieve the previous node from a particular node since it's implementing doubly-linked lists?

[ramyagunaseelan]

If same hashcode here for different keys then? what about collision and threshold applies
naveen pls reply

[nehasinghal]

How the collision is handled in LinkedHashMap?

[chetanpalekar]

Hi Naveen, Thank you for this explanation. Just a quick query, what happens here, if the segment index of the second value I am inserting is calculated to be the same as the index of the first value? In your HashMap implementation video example you have had mentioned that the segment index of different values can be the same. Is is not the same for LinkedHashMap?

Thanks!!

[xyfqnme]

Hi, Thank you for the explanation, but I have a question when a collision occurs how the behavior be? because we are already pointing before and after node?

[mollamainuddin]

If in case of LinkedHashMap collisions is occured then what will happen?

[socialmedia]

Hi Naveen, can collision occur in the LinkedHasMap also. In that case what happens to the before and after nodes?

[sheshankgolli]

While we are inserting next elements, if we get index is lesser than the previous node, how they will connect before and after and maintains the insertion order. ?

[RajkumarVishwakarma]

Sir what happens if index for 2 different keys is same.. Then how the two key value pairs will be stored?

[TheRajatsaluja]

Naveen can you share the collision in case of LinkedHashMap

[moonshine]

Since index is decided is based on hash code, how is it ordered collection ? What if some key get index of 2 (which is inserted in the end) & what about Collison? Doesn't it happen here?? I understood o/p will be just like i/p tho.

[kanishkasrivastava]

and what will happen when collision happens. Even in HashMap values are stored in the same way. What's the difference between HashMap and LinkedHashMap.