Enthuware

Just wanted to note that,
If the array 'sa' has objects other than String that don't implement comparable, java.lang.ClassCastException will be thrown at runtime.

No, sa can never have objects other than Strings.

I mean Animal[] sa= {new Animal("dog"), new Animal("cat"), new Animal("elephant")}

where Animal is a valid class with constructor that takes string

What I don't understand is why "sa" is effected by "Comparator.sort(Arrays.asList(sa), null)". I would expect "Arrays.asList(sa)" to generate a NEW ArrayList (or something similarly appropriate extending List) which will get lost because it is not saved to a reference variable. Why does "Arrays.asList()" sort the underlying String[]?

Because the list is backed by the array as explained in the [url=https://docs.oracle.com/javase/8/docs/a ... l#asList-T...-]JavaDoc API description of Arrays.asList method[/b]. Anything you do to the list actually happens on the underlying array.

One important habit that the part 1 exam (i.e OCA) inculcates is to read the JavaDoc. That should be your first source of information.