Why is LinkedList replaced by TreeMap inside a hash table bucket in cases with a large number of elements?

In the implementation of a hash table (for example, in Java's HashMap), when there are many collisions in a single bucket, a LinkedList is replaced with a TreeMap to improve performance.

The reason is that a LinkedList takes O(n) time to find an element — you need to traverse all elements in the list. If there are many elements in the bucket, this significantly slows down operations.

A TreeMap, on the other hand, implements a balanced tree (usually a red-black tree), where search, insertion, and deletion are performed in O(log n). Therefore, when the number of elements in a bucket exceeds a threshold (for example, 8), the structure is changed to a TreeMap to speed up operations and avoid performance degradation.

Thus, replacing a LinkedList with a TreeMap inside a bucket is an optimization that allows efficient operation of the hash table even with a large number of collisions.