As per Java API spec, the signature of Collections.reverseOrder is
public static
And the example gi
T is being resolved to Object. This passes, since Arrays.sort(T[], Comparator super T>) would accept a Comparator, since Object is a supertype of T.
Eclipse confirms that Collections.reverseOrder() is resolved to a Comparator in the code
String[] array = new String[10];
Arrays.sort(array, Collections.reverseOrder());