I would agree if I were adding a dependency to Gradle or something. In this case it’s just something that conforms to the same interface as the other Map and is built into every Java for the last 20+ years. The max amount of effort I am wasting here is the ten extra characters I used to type “Concurrent”.

My point was that even if it is not optimal, there’s really no utility in bickering about it because it doesn’t really change anything. The savings from changing it to regular hashmap will, generously, be on the order of nanoseconds in most cases, and so people getting their panties in a bunch over it seems like a waste of time.