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

From looking at the Collections source, it looks like Unmodifiable does not make it synchronized.

static class UnmodifiableSet extends UnmodifiableCollection
                 implements Set, Serializable;

static class UnmodifiableCollection implements Collection, Serializable;

the synchronized class wrappers have a mutex object in them to do the synchronized parts, so looks like you need to use both to get both. Or roll your own!