How is the internal implementation of LinkedHashMap different from HashMap implementation?

Question

I read that HashMap has the following implementation:

main array 
   ↓
[Entry] → Entry → Entry      ← linked-list implementation
[Entry]
[Entry] → Entry
[Ent         


        

Answer 1

So, it has an array of Entry objects.

Not exactly. It has an array of Entry object chains. A HashMap.Entry object has a next field allowing the Entry objects to be chained as a linked list.

I was wondering how can an index of this array store multiple Entry objects in case of same hashCode but different objects.

Because (as the picture in your question shows) the Entry objects are chained.

How is this different from LinkedHashMap implementation? Its doubly linked list implementation of map but does it maintain an array like the above and how does it store pointers to the next and previous element?

In the LinkedHashMap implementation, the LinkedHashMap.Entry class extends the HashMap.Entry class, by adding before and after fields. These fields are used to assemble the LinkedHashMap.Entry objects into an independent doubly-linked list that records the insertion order. So, in the LinkedHashMap class, the entry objects are in two distinct chains:

• a singly linked hash chain that is accessed via the main hash array, and

• a separate doubly linked list of all entries that is kept in entry insertion order.