/**
* Gets random value from given collection.
*
* @param c Input collection (no {@code null} and not emtpy).
* @return Random value from the input collection.
*/
@SuppressWarnings("UnusedDeclaration")
private static <T> T rand(Collection<? extends T> c) {
if (c == null) throw new IllegalArgumentException();
int n = ThreadLocalRandom.current().nextInt(c.size());
int i = 0;
for (T t : c) {
if (i++ == n) return t;
}
throw new ConcurrentModificationException();
}
