Concurrent hashmap size() method complexity
concurrency, concurrenthashmap, java, java.util.concurrent
Solution
It isn't. In my version of the JDK, `HashMap.size()` has `O(1)` complexity, whereas `ConcurrentHashMap.size()` in the best case has to iterate over the segments. In the worst case it will lock all segments, which can be a pretty expensive operation in a multithreaded scenario.
Of course, which is faster is a different question altogether. The answer largely depends on how many threads are accessing the map, and what it is exactly that they are doing.
Problem
I'm wondering if the `size()` method invoked on `ConcurrentHashMap` is of the same complexity as the `size()` method for usual HashMap.