What improvements were made to the HashMap implementation in Java 8 compared to previous versions?

In Java 8, the implementation of HashMap introduced the following key improvements:

• Use of balanced trees (TreeBins): When there are many collisions in a single bucket (more than 8 elements), the linked list is replaced with a red-black tree. This improves search operation performance from O(n) to O(log n) in the worst case.

• Hash distribution optimization: The hashing algorithm was improved for a more uniform distribution of keys across buckets, reducing the likelihood of collisions.

• Support for parallel streams: Although HashMap itself is not thread-safe, the improvements in data structure facilitate more efficient operation in a multithreaded environment when using external synchronization.

These changes significantly enhanced the performance and robustness of HashMap when working with large data volumes and collisions.