What is the advancement made in Hashmap in Java 8?

We'll talk about an intriguing update on HashMap performance Improvement Changes in Java 8. Due to a performance issue, the Oracle changed HashMap. 

What is HashMap and How it is Implemented?

It keeps the key-value pair in storage where it may be retrieved with the use of a key. You must be familiar with how HashMap is Implemented only then we can understand what was the performance issue we had earlier and how that has been overcome by Oracle in Java 8.

As its name suggests, HashMap operates on the concept of hashing.

Equals() and hashcode() are two of the methods included in the Java Object class. We need to appropriately override these methods in order to get our HashMap to behave as expected.

Any problems with these approaches could even invalidate the entire purpose since there is a chance that the results won't be retrieved even if the key-value pair is still there.

HashMap use the Basic Implementation of Map Interface.

When there is a hash collision, the entry's LinkedList is generated to save the item in the hash map. In other words, a bucket containing a list of all the key-value pairs with keys that have the same hash code is formed on each hash collision.

The equals() method finishes the work by returning the correct key after hashcode generates the hash and supplies the appropriate bucket.

Advancement Made in Java 8

Since Java 8, Hash Map's Linked List has been replaced with another type of Data Structure names Binary Tree.

This will happen only when the linked list reaches the TREEIFY_THRESHOLD value.

Once this limit is reached, then the LinkedList is converted into a tree structure, leaving the time complexity to O(log(n)) from O(n).

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