Does the unmodifiable wrapper for java collections make them thread safe?

Question

I need to make an ArrayList of ArrayLists thread safe. I also cannot have the client making changes to the collection. Will the unmodifiable wrapper make it thread safe or d

Answer 1

The unmodifiable wrapper only prevents changes to the structure of the list that it applies to. If this list contains other lists and you have threads trying to modify these nested lists, then you are not protected against concurrent modification risks.