Why is CopyOnWriteArrayList different than iterating over unmodifiableList?

Question

I am not able to understand why can't we achieve by just iterating over an immutable list rather than using this new implementation?

Answer 1

The javadoc of CopyOnWriteArrayList states

A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array.

While the javadoc of Collections#unmodifiableList(List) states

Returns an unmodifiable view of the specified list. This method allows modules to provide users with "read-only" access to internal lists.

Query operations on the returned list "read through" to the specified list, and attempts to modify the returned list, whether direct or via its iterator, result in an UnsupportedOperationException.

So, no, you can't get the features provided by CopyOnWriteArrayList with a List returned by Collections#unmodifiableList(List).