java.util.Date: seven days ago

try

 Date sevenDay = new Date(System.currentTimeMillis() - 7L * 24 * 3600 * 1000));

Another way is to use Calendar but I don't like using it myself.

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).

Use Calendar's facility to create new Date objects using getTime():

import java.util.GregorianCalendar;
import java.util.Date;

Calendar cal = new GregorianCalendar();
cal.add(Calendar.DAY_OF_MONTH, -7);
Date sevenDaysAgo = cal.getTime();