Can you explain the internal structure and working mechanism of a hash table in Java?

The hash table in Java (e.g., HashMap) is a data structure that stores key-value pairs and provides fast access based on the key.

Internal structure:

• It is based on an array of buckets.
• Each bucket contains either null or a linked list (or tree if many elements) of entries with the same hash code modulo the array size.

How it works:

1. When adding an element, its hash code is computed, and the index in the array is determined.
2. If the bucket is empty, the element is placed there.
3. If the bucket is occupied, a search is performed in the linked list (or tree) for a matching key:
   • If found, the value is updated.
   • If not, the element is added to the list.
4. When the load factor exceeds a threshold, the array is resized (rehash) to maintain performance.

This approach provides average operation complexities close to O(1) for insert, search, and delete.

Example usage:

Map<String, Integer> map = new HashMap<>();
map.put("key1", 100);
Integer value = map.get("key1"); // fast retrieval by key