<i>It doesn’t have a calendar system.</i><p>Hopefully this won't come off as mere quibbling about terminology, but to me it makes more sense to say that it <i>does</i> have a calendar system, it's just that it isn't any of the ones humans use. When I write "April 23, 2017 6:04pm CDT", the calendar system is Gregorian. If I were to write the integer value underlying a java.util.Date, I would argue the calendar system is Unix Epoch.<p>Both are systems that pick out arbitrary points in history (year 1 AD or midnight January 1, 1970) to base numbers off of. Both have rules on how you manipulate those numbers and what values mean.<p>If someone persists in asking what the time zone is for a java.util.Date, I would probably tell them that, more or less, it has <i>its own</i> time zone. This isn't quite true, but it's close because time zones are basically parameters for parameterized calendar types, so a time zone kind of implies a calendar.<p>Anyway, the point is that thinking of it as its own calendar system hopefully makes it clear that it stands on its own.