Rotating lists in linear time and constant space (Java) - follow-up
Input validation

If the list is empty, there will be division by zero.
Since you check for null input list,
it would make sense to do likewise for empty list as well.

Type parameter

The &lt;T&gt; is not needed in the Collections.&lt;T&gt;reverse statements,
this works just fine:

Collections.reverse(list);
Collections.reverse(list.subList(0, rotationCount));
Collections.reverse(list.subList(rotationCount, list.size()));