Collections.unmodifiableList and defensive copy

Question

If I write

List a1 = Arrays.asList(1, 2, 3);
List a2 = Collections.unmodifiableList(a1);

a2 is r

Answer 1

If you need unmodifiable and immutable list or in other words unmodifiable copy of the source list without any dependency to other libraries try this:

Collections.unmodifiableList(Collections.list(Collections.enumeration(sourceList)))

Collections.list() copies values from its enumeration.