Date calculation

[auvrm papu]

How to find date ( probably in long) of 7 days before today?

[Bear Bibeault]

Check out java.util.Calendar.

Or simply do some math on the long value.

[auvrm papu]

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

[Henry Wong]

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]

I used the following

 Long today = new Date().getTime();   

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

[Henry Wong]

Originally posted by Ais Kaly:
I used the following

 Long today = new Date().getTime();   

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

[Rob Spoor]

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:

Calendar calendar = Calendar.getInstance(); // points to NOW
// if you have a specific Date object you can set it:
//calendar.setTime(date);
calender.add(Calendar.DATE, -7); // subtract 7 days
// get a Date object if needed:
//date = calendar.getTime();