What is the average difficulty level of searching for an element by key in HashMap?

On average, searching for an element by key in a HashMap in Java has a complexity of O(1), which is constant time. This is achieved through the use of a hash function that quickly determines the index in the array where the element is stored.

However, in the worst case (for example, with a large number of collisions), the complexity can degrade to O(n), where n is the number of elements in a single bucket. Modern implementations of HashMap use balanced trees to store collisions, which improves the worst case to O(log n).