About Question enthuware.ocpjp.v7.2.1624 :

[boyonsea]

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.

[admin]

No, sa can never have objects other than Strings.

[boyonsea]

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

where Animal is a valid class with constructor that takes string

[bvrulez]

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[]?

[admin]

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.

[admin]

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.

[lucavassos]

Regarding this:

Although not documented in the JavaDoc API description, passing null doesn't cause a NullPointerException.

I think the docs are stating that pretty clearly:

The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.

[admin]

Note sure which class's JavaDoc are you looking but Collections.sort doesn't throw NPE if the second argument is null.
The code given in the question works fine:
String[] sa = { "charlie", "bob", "andy", "dave" };
Collections.sort(Arrays.asList(sa), null);