performance - What is the time complexity of HashMap.containsKey() in java?

Question

I need to know: What is the time complexity of HashMap.containsKey() in java?

Answer 1

From the API doc ofHashMap:

This implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets.

Since containsKey() is just a get() that throws away the retrieved value, it's O(1) (assuming the hash function works properly, again).