Enthuware

Option B: remove(Object key) returns V, not boolean

Right. That is why it is not the correct option.

The explanation is clear, but only from options description one gets the impression that the methods are atomic in the Map interface.

I see boolean remove(Object key, Object value) int specification here:
https://docs.oracle.com/en/java/javase/ ... ntMap.html

But in the answers, it is marked as an incorrect option.
Some kind of confusion.

Yes, but the question asks for methods that are there in ConcurrentMap in addition to Map. The method you have mentioned exists in Map that is why it is not a correct option.