java - Are leap seconds catered for by Calendar?

Question

Are leap seconds catered for by the GregorianCalendar class?

If not, does any 3rd party library cater for it?

Answer 1

1. Leap seconds are not catered for by GregorianCalendar (a view of the source code at Oracle shows this - explicit assumption of 1 minute = 60 seconds always is given there). And furthermore: Oracle has now officially denied leap second support - see Bug-ID 4272347.
2. In Java there is no standard 3rd party library supporting leap seconds - not even joda-time. Only specialized software like this does that.
3. Note that many libraries do talk about leap seconds although not supporting, for example java.util.Date (see Dorofeevs answer). Also JSR 310 talks a lot, but does not support this feature. Officially JSR 310 gives support to UTC-SLS which does not count leap seconds and only describes smearing rubber seconds around a leap second event. Indeed JSR 310 is very confusing about if it supports UNIX time or UTC-SLS (see next point). And since leap second information (github/threeten/issues/197) has been removed from JSR 310 code base it is absolutely impossible to implement true UTC leap seconds within the scope of JSR 310. In best case you might expect a coming external module (Threeten-Extra) as supplement for JSR 310 which will give rudimentary support at best (it is rather a translation between UNIX time and TAI time scale, not more and uses in my opinion a fundamentally wrong domain model).
4. System.currentTimeMillis() officially relates to OS timer. And since all OS I know including Microsoft, Linux and Apple are only based on UNIX specification this java system timer does not count leap seconds, only the normal milliseconds since 1970-01-01T00:00:00.000Z
5. Because of all these facts I have decided to set up my own date and time java library named Time4J which fully supports leap seconds and is available as v1.0 with LGPLv2.1-licence. A dzone-article demonstrates how this support looks like with version v4.2.