jodatime - Joda DateTime output unexpected difference from gmt -

my code:

  val pattern = "mm-dd-yy"   val t = datetime.parse("07-01-86", datetimeformat.forpattern(pattern)).todatetime(datetimezone.forid("gmt"))   val z = t.getmillis.asinstanceof[long]   println("ms= "+z) // expected output: 520560000000  actual output: 520578000000 

several online gmt date converters give different millis output datetime. know why?

in solution local time zone implicitly used when parsing date time. should use

val t = datetime.parse("07-01-86", datetimeformat.forpattern(pattern).withzoneutc()) 

to force datetime created in utc zone. then, millis 520560000000. no need execute todatetime(datetimezone) on more.

otherwise, construction

val t = datetime.parse("07-01-86", datetimeformat.forpattern(pattern)).todatetime(datetimezone.forid("gmt")) 

the datetime first created in local tz (ie. midnight of 07-01-86 in your tz) , "cast" utc, preserving timestamp (ie. same timestamp, interpreted in utc, time part , day part change depending on local tz offset).

example (my tz +02:00):

datetime.parse("07-01-86", datetimeformat.forpattern(pattern)) // --> 1986-07-01 00:00 (+02:00) .todatetime(datetimezone.forid("gmt"))                         // --> 1986-06-30 22:00 (utc) 

i assumed ok using utc on gmt there's also

datetimeformat.forpattern(pattern).withzone(...) 

where can provide desired zone.