Joda time has this concept, it calls it a partial http://joda-time.sourceforge.net/key_partial.html http://joda-time.sourceforge.net/key_partial.html . A partia

Joda time has this concept, it calls it a partial http://joda-time.sourceforge.net/key_partial.html http://joda-time.sourceforge.net/key_partial.html . A partial is a datetime without a time zone, so it only partially specifies a time. You can combine a partial with a timezone to get an instant, a fully specified date time. It's also interesting to note that some operations cannot be performed with partials. For example, you can't add an instant and a partial (because that would be buggy). In order to add them, you have to first convert the partial to an instant (by specifying a timezone). In the parent's example, nap time would be a partial of 15:00, and your calendar app would notify about nap time by specifying the current timezone of the computer.