Question

hi im trying to convert a date value in milliseconds granuality into java Date using
new Date( millsecs)
the converted value i get is 3 hours behind what it is supposed to be.

I tried using online tools to conver the millisec value i have and it convert to correct date.
Can some one point out what im missing!!!

thnx

Answer 1

A java.util.Date does not have an hour — at least not in the way that you probably mean. Try the following, and you’ll see that the date simply is a point in time that you can specific as X milliseconds since epoch:

long millisec = System.currentTimeMillis();
Date date = new Date(millisec);
long millisec2 = date.getTime();

If I print this date in New York City’s time zone, it will correspond to some hour of the day. If I print the same date in GMT, then the hour will be four larger. You probably are printing the value in such a way that you see the same time zone effect.

Think of a date as a point in time. That’s a specific number of milliseconds since epoch. Let’s pick 3PM PDT as our point in time. This corresponds to 6PM EDT. In other words, all three of those values (millseconds since epoch, 3PM PDT, and 6PM EDT) occupy the same spot on on a timeline.

Or, here’s another explanation. 3PM PDT on some day is NOT the same as 3PM EDT on that day. Let’s say 3PM PDT corresponds to M milliseconds since epoch. Then, 3PM EDT = M – 10,800,000 milliseconds (that’s the number of milleseconds in three hours).