String[] names = { "UNUSED", "Monday", "Tuesday", ... }
  try { 
    return names[i];
  } catch(ArrayIndexOutOfBoundsException uhoh) {
    return "???";
  }

It's so easy...

Look, at least it's not a pile of @Inject DayOfWeekLookupAdapter dayOfWeekLookupAdapter with attendant 100kB Spring XML config, of which the unit tests will have their very own special cut and pasted copy. No, I'm not bitter at all.