Convert date between java and .net - 2 days off

Question

I need to transform a .NET DateTime to an equivalent Java Calendar representation.

The .NET DateTime uses Ticks

Answer 1

From the Java documentation:

[...] dates obtained using GregorianCalendar are historically accurate only from March 1, 4 AD onward, when modern Julian calendar rules were adopted

Considering your DateTime subtraction, it's only a Ticks difference, there is absolutely no notion of a specific calendar here. The implementation is basically return new TimeSpan(x.Ticks - y.Ticks).

You might be better at simply outputting then parsing an ISO-8061 date/time such as 0001-02-03T00:00:00Z, which has no ambiguity, rather than relying on the internal representation.