From exactly now:
long DAY_IN_MS = 1000 * 60 * 60 * 24;
new Date(System.currentTimeMillis() - (7 * DAY_IN_MS))
From arbitrary Date date:
new Date(date.getTime() - (7 * DAY_IN_MS))
Edit: As pointed out in the other answers, does not account for daylight savings time, if that’s a factor.
Just to clarify that limitation I was talking about:
For people affected by daylight savings time, if by 7 days earlier, you mean that if right now is 12pm noon on 14 Mar 2010, you want the calculation of 7 days earlier to result in 12pm on 7 Mar 2010, then be careful.
This solution finds the date/time exactly 24 hours * 7 days= 168 hours earlier.
However, some people are surprised when this solution finds that, for example, (14 Mar 2010 1:00pm) - 7 * DAY_IN_MS may return a result in(7 Mar 2010 12:00pm) where the wall-clock time in your timezone isn’t the same between the 2 date/times (1pm vs 12pm). This is due to daylight savings time starting or ending that night and the “wall-clock time” losing or gaining an hour.
If DST isn’t a factor for you or if you really do want (168 hours) exactly (regardless of the shift in wall-clock time), then this solution works fine.
Otherwise, you may need to compensate for when your 7 days earlier doesn’t really mean exactly 168 hours (due to DST starting or ending within that timeframe).