I know I can get the current date using new Date(), but I want to get a past date (12 weeks back). For example: today is Jan 3rd 2014, a 12 weeks old date would be Oct 11 2013.
How to do that in java?
Asked
Active
Viewed 1,272 times
2
eebbesen
- 5,070
- 8
- 48
- 70
user3155754
- 31
- 4
-
[Here](http://docs.oracle.com/javase/tutorial/datetime/) is the 'official' tutorial focused on 1.8. – eebbesen Jan 03 '14 at 03:07
5 Answers
10
Date date = new Date();
long timeAgo = 1000L * 60 * 60 * 24 * 7 * 12;
Date dateAgo = new Date(date.getTime() - timeAgo);
Should work just fine. Don't miss the L from the multiplication, otherwise you'll get overflow results. Good spot by Pshemo.
FYI, the timeAgo columns are as follows:
1000 is representative of a second (1000 milliseconds)
1000 * 60 is representative of a minute (60 seconds)
1000 * 60 * 60 is representative of an hour (60 minutes)
1000 * 60 * 60 * 24 is representative of a day (24 hours)
1000 * 60 * 60 * 24 * 7 is representative of a week (7 days)
1000 * 60 * 60 * 24 * 7 * 12 is representative of 12 weeks (12 weeks)
-
2@Alex the above allows for more customisable situations. Plus, it explains the logic for calculating time which is useful to anyone. – whitfin Jan 03 '14 at 03:09
-
-
-
1@Alex Say he wants to then do it in some other language without the same libraries. How does he do it without knowing the logic behind it? Ask again based on that language? I agree, code should be to the point - but there is a time and place for that. – whitfin Jan 03 '14 at 03:16
-
-
@Alex That's kinda my point. But anyway, under someone else's answer isn't the place to get offended that their answer got more upvotes than yours, so let's leave it there. – whitfin Jan 03 '14 at 03:20
-
1This approach is error-prone (and you showed it). Try printing `dateAgo` and you will be surprised with result. It is better to use build in methods to avoid surprises like [integer overflow](http://en.wikipedia.org/wiki/Integer_overflow). – Pshemo Jan 03 '14 at 03:30
-
2The problem with is approach is it to easy to trip over irregularities in date/time. Not every day is is exactly 24 hours long and leap years, century and millennium boundaries all add it additional considerations... – MadProgrammer Jan 03 '14 at 03:33
-
@Pshemo Valid point. And MadProgrammer that's also valid, but that might be the desired behaviour. For example, it works for this question (we need specifics to go further). – whitfin Jan 03 '14 at 03:35
-
Actually it doesn't work. Your `timeAgo` will overflow to `-1332334592` so in reality by `-timeAgo` you are adding `1332334592` milliseconds to current date. – Pshemo Jan 03 '14 at 03:38
-
@Pshemo Oops, been using jscript too much and forgot about my ints. Fixed it now. – whitfin Jan 03 '14 at 03:53
-
1Dont use `l` to specify `long` (it looks more like `1`). Use `L` instead. Also try adding this suffix to your first operand `1000L` to make result of first multiplying (and by that also others) `long`. It helps making sure that you will not overflow integer before you will multiply it with last operand `12L`. – Pshemo Jan 03 '14 at 04:14
8
Most of Date is actually deprecated, it has been superseded by Calendar:
Calendar.getInstance().add(Calendar.WEEK_OF_YEAR, -12);
Elliott Frisch
- 198,278
- 20
- 158
- 249
Njol
- 3,271
- 17
- 32
6
Use LocalDate.minusWeeks of JDK 1.8,
LocalDate first=LocalDate.now();
LocalDate second=first.minusWeeks(12);
Masudul
- 21,823
- 5
- 43
- 58
3
I am surprised no one mentioned Joda Time yet.
DateTime dt = new DateTime();
System.out.println(dt);
System.out.println(dt.minusWeeks(12));
System.out.println(dt.minusWeeks(12).toDate());//if you prefer Date object
Output:
2014-01-03T04:40:40.402+01:00
2013-10-11T04:40:40.402+02:00
Fri Oct 11 04:40:40 CEST 2013
Pshemo
- 122,468
- 25
- 185
- 269
