Thread: Year help

I'm not really sure where to post this so I will do it here.
I want to make a counter for days, months and years. The days and months will not be very hard, but the problem is years. As everyone knows every 4 years there is one more day in the year. How would I make this in the counter? I want it to be able to run from the year 1.000 until the year 25.000 (in other words every possible year) and every 4 years have a day extra.
How would I be able to let the counter require 1 more day every 4 years?
I think that I will need some math formula for it. (Is formula the right word?)

Is there a reason why you're not using GregorianCalendar?

GregorianCalendar (Java 2 Platform SE 5.0)

I didn't know it existed. Thanks