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 were looking to keep a1 mutable and make an immutable copy of it without Guava, this is one way you could do it.

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