What is the search speed in HashMap (average and worst case)?

HashMap in Java provides an average access time to an element of about O(1) due to the use of a hash function for quick key lookup.

However, in the worst case, when there are many collisions and all elements end up in a single bucket, the access speed can degrade to O(n), where n is the number of elements in the map.

Starting from Java 8, when there are many collisions within a single bucket, the data structure changes from a linked list to a balanced tree (TreeMap), which improves the worst-case access time to O(log n).

Example:

HashMap<String, Integer> map = new HashMap<>();
map.put("key1", 100);
Integer value = map.get("key1"); // Average time O(1)