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

a1 and a2 will reference the same data (memory).

the un-mofifiable part comes , only with a2 as entry.

imaging if you are passing a2 to a method where you expect the method to be idempotent. such cases a2 helps.

in summary you cant modify data using a2 pointer.