What are the access speeds to elements in HashMap during basic operations?

Access to elements in HashMap during basic operations (get, put, remove) is O(1) in the best case (assuming uniform distribution of hash codes and no collisions).

In the presence of collisions and their resolution by chaining (linked lists), the worst-case access time can reach O(n), where n is the number of elements in the "bucket", as it requires traversing the linked list to find or insert an element.

Starting from Java 8, to improve performance with many collisions in a single "bucket", the linked list is converted into a balanced tree (e.g., red-black tree). In this case, the worst-case access time with collisions is reduced to O(log n). This significantly improves performance in scenarios with many collisions.

The actual speed depends on:

• Hashing function: A good hash function minimizes collisions.
• Hash table load factor: A high load factor increases the likelihood of collisions. When the threshold is exceeded, the HashMap is resized (rehash), which can be an expensive operation O(n).
• Presence and number of collisions.
• Type of stored data: Types that correctly implement hashCode() and equals() provide better performance.