How does ConcurrentHashMap work internally?

Question

I was reading the official Oracle documentation about Concurrency in Java and I was wondering what could be the difference between a Collection returned by

Answer 1

Returned by synchronizedCollection() is an object all methods of which are synchronized on this, so all concurrent operations on such wrapper are serialized. ConcurrentHashMap is a truly concurrent container with fine grained locking optimized to keep contention as low as possible. Have a look at the source code and you will see what it is inside.