Unexpected result subtracting 24 hours from date 03/25/2018

Question

I am subtracting 24 hours from a GregorianCalendar 03/25/2018 09:41.

Result 03/24/2018 08:41.

public class Utiles{
    public static void main(String args[]) {

        SimpleDateFormat sdt = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
        GregorianCalendar gcFinAux = new GregorianCalendar(2018, 2, 25, 9, 41, 0);

        System.out.println("1. " + sdt.format(gcFinAux.getTime()));
        gcFinAux.add(Calendar.HOUR_OF_DAY, -24);
        System.out.println("2. " + sdt.format(gcFinAux.getTime()));
    }
}

Output:

1. 25/03/2018 09:41:00
2. 24/03/2018 08:41:00

If I try with another date the result is correct.

I try in Linux and Windows with JDK1.6.0_45 and Java 1.8.

Could someone confirm if you get the same results?

Thank you.

Yes, daylight saving time is real. If you don't like it, sign this petition: https://www.change.org/p/british-government-motion-to-abolish-daylight-savings — baao, Mar 23 '18 at 10:57
[daylight saving time](https://www.timeanddate.com/time/dst/2018.html) — Federico klez Culloca, Mar 23 '18 at 10:57
Consider switching to `java.time`. Makes things much easier. — lexicore, Mar 23 '18 at 10:57
The date API you are using is **legacy**. Use the classes of the `java.time` package instead. — Zabuzard, Mar 23 '18 at 11:22
I get the same result (I am in Europe/Copenhagen time zone, so this is also what I had expected). — Ole V.V., Mar 23 '18 at 12:38
Related: [Java ZonedDateTime to Instant conversion](https://stackoverflow.com/questions/49099735/java-zoneddatetime-to-instant-conversion) — Ole V.V., Mar 23 '18 at 12:43

score 0 · Answer 1 · answered Mar 23 '18 at 10:58

0

I know some parts of the world have time changes during that specific 24 hr period. Sounds like the underlying logic is taking that into account.

answered Mar 23 '18 at 10:58

Chris Gerken

16,221
6
44
59

Ole V.V. · Answer 2 · 2018-03-25T09:54:53.317

As has been said in the comments, what you observed is the expected and correct behaviour in time zones that change to summer time (DST) during the night between March 24 and March 25 this year. This includes most of Europe including Spain, not (the European parts of) Turkey and Russia, but also for example Greenland and Lebanon (while Paraguay changes back from summer time the same night).

java.time: As lexicore and Zabuza said in comments, there is really no reason why you should want to use SimpleDateFormat and GregorianCalendar. Those classes are long outdated and the former in particular notoriously troublesome. Instead use java.time, the modern Java date and time API:

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss");
    ZonedDateTime zdtFinAux 
            = ZonedDateTime.of(2018, 3, 25, 9, 41, 0, 0, ZoneId.of("Europe/Madrid"));

    System.out.println("1. " + zdtFinAux.format(formatter));
    zdtFinAux = zdtFinAux.minusHours(24);
    System.out.println("2. " + zdtFinAux.format(formatter));

The output is the same as yours, of course:

1. 25/03/2018 09:41:00
2. 24/03/2018 08:41:00

If you wanted the same time of day on the previous day, one option is to use minusDays(1) instead of minusHours(24).

Links

Clock changes in Madrid, Spain (provided for non-European readers).
Oracle tutorial: Date Time explaining how to use java.time.

Unexpected result subtracting 24 hours from date 03/25/2018

2 Answers2