In comp.lang.java.programmer message <7ng5mrF3lbplvU1@mid.dfncis.de>,
Sun, 29 Nov 2009 22:11:22, Lars Uffmann <aral@nurfuerspam.de> posted:
Is anyone able to tell me how I can tell this Calendar class to do
proper date calculation? I don't want to do everything by hand,
accounting for leap years - I just want to add a certain amount of days
to a date and get the date of the result...
Gregorian Date day arithmetic is trivial if one has arithmetical
routines to convert between a Y M D triple and a day-count. A variety
of algorithms for that, with tests, in JavaScript, can be found in
<URL:http://www.merlyn.demon.co.uk/daycount.htm> ; translation to Java
should be easy for anyone who knows and can run Java.
Any Java library with Date routines should provide, and document,
corresponding conversions, carefully avoiding any need to determine
Summer Time either implicitly or explicitly.
Month arithmetic is trivial by converting to/from month-count, except
that one must decide what to do if the starting day number is too large
for the finishing month.
Year arithmetic is trivial, except that one must decide what to do if
the starting date is February 29 and the finishing year is not leap.
Rarely will it be possible to code *significantly* briefer or faster.