What elements or features of the internal structure of HashMap cannot be changed after its creation?

The internal structure of HashMap in Java includes a bucket array, where each bucket contains a linked list or a tree (in newer versions) of elements with the same hash. After creating a HashMap, you cannot directly change the size of the bucket array — it is automatically resized during rehashing when a certain load factor threshold is reached.

Also, you cannot change the hash function used inside the HashMap, as it is built into the implementation.

As for the elements (Entry), keys and values can be changed if you have access to the objects, but the structure of the keys themselves (such as their hash code or equals method) cannot be changed, as this would break the integrity of the map.

In summary, the main immutable elements after creating a HashMap are:

• The size of the internal bucket array (only changed automatically)
• The hash function
• The structure of storing elements (linked lists or trees) — cannot be directly changed, only through Map methods

Example: you cannot manually change the size of the bucket array or the hash function, but you can add and remove key-value pairs.