Does HashMap guarantee a specified complexity for element retrieval?

HashMap guarantees an average O(1) complexity for element retrieval (get). In the worst case, when all elements fall into one bucket (for example, with poor hash code distribution), the complexity increases to O(n), where n is the number of elements. From Java 8 onwards, when there are many collisions in one bucket, a tree structure (red-black tree) is used instead of a list, which reduces the worst-case complexity to O(log n).