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# Date calculation

Ranch Hand
Posts: 105
How to find date ( probably in long) of 7 days before today?

Author and ninkuma
Marshal
Posts: 66730
167
Check out java.util.Calendar.

Or simply do some math on the long value.

auvrm papu
Ranch Hand
Posts: 105
Thanks Bear,
Can someone please elaborate on how do I go about doing calculations in Long?

For Ex: 1227306791752
this should pretty much represent Nov 21, 2008 around 4.33 pm

But I don't understand how those numbers are represented

author
Sheriff
Posts: 23556
138

But I don't understand how those numbers are represented

Well, it's your data!! You have to tell us how it is represented !! Different systems have different representations.

Now, if this is the same as the long that is returned from the System clas, then the value is "the difference, measured in milliseconds, between the [represented] time and midnight, January 1, 1970 UTC".

Henry

auvrm papu
Ranch Hand
Posts: 105
I used the following

[ November 21, 2008: Message edited by: Ais Kaly ]

Henry Wong
author
Sheriff
Posts: 23556
138

Originally posted by Ais Kaly:
I used the following

That's the same representation as the System class. It's the current time, measured in milliseconds, from January 1st, 1970 UTC.

So, to subtract a week, just subtract a week's worth of milliseconds.

Henry

Sheriff
Posts: 21379
92
I object!

Usually subtracting a week's worth of milliseconds is not a problem. However, there is this nasty thing called "daylight savings time", that once a year makes a day 23 hours and once a year 25 hours. This makes the calculation inaccurate if the hours is before 1 am or after 11 pm.

I'll second Bear's recommendation of Calendar: