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java.util.Date special date 1980-04-06: wrong hour

We faced following problem:
SimpleDateFormat formatter = new SimpleDateFormat("dd-MM-yyyy", java.util.Locale.GERMAN);
String dateInString = "06-04-1980";
Date date = formatter.parse(dateInString);
before: Sun Apr 06 00:00:00 CEST 1980
after: Sun Apr 06 01:00:00 CEST 1980
Another example:
Date date = Date.from(LocalDate.of(1980, 4, 6).atStartOfDay(ZoneId.systemDefault()).toInstant());
Facing the same problem.
We thought change of java11 to java17 is the problem, but it wasn't. It was the change of the timezone from Europe/Berlin to Europe Vienna. On 1980-04-06 the daylight saving time was established in Austria and the change of the hour was at 00:00. So there was no 00:00 at this date.
Reproduceable example - changing timezone to "Europe/Berlin" results in 0 hour.
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd.MM.yyyy");
for (LocalDate date = LocalDate.of(1500, 04, 01); date.isBefore(LocalDate.of(9999, 1, 1)); date = date.plusDays(1)) {
Date out = Date.from(date.atStartOfDay(ZoneId.of("Europe/Vienna")).toInstant());
Calendar cal = Calendar.getInstance();
cal.setTimeZone(TimeZone.getTimeZone(ZoneId.of("Europe/Vienna")));
cal.setTime(out);
if (cal.get(Calendar.HOUR_OF_DAY) > 0) {
System.out.println(date.format(formatter) + " > " + cal.get(Calendar.HOUR_OF_DAY));
}
}
System.out.println("done");
All dates before 1893-03-31 have 23 as hour in timezone "Europe/Vienna", in "Europe/Berlin" its also 0.

It's not really a problem, it's a special thing about timezone "Europe/Vienna" which was changed in our system. If you get this problem, check your timezone, maybe it was changed by some other properties.
While summer time (DST) started at 02:00 o’clock in Germany on that date, it started already at midnight in Austria (Europe/Vienna time zone), so the time 00:00 did not exist, which is why we suddenly got 01:00. Both time zones are printed as CEST (Central European Summer Time), so the abbreviation does not allow us to distinguish.

I am in Israel, so in order to simulate the time zone of central Europe (using Java 17), I set the [System] property user.timezone to CET using the -D option of the java command. Then I ran the following code:
/*
* import java.time.ZoneId;
* import java.time.ZonedDateTime;
* import java.util.Date;
*/
ZonedDateTime zdt = ZonedDateTime.of(1980, 4, 6, 0, 0, 0, 0, ZoneId.systemDefault());
System.out.println(Date.from(zdt.toInstant()));
The result I got was:
Sun Apr 06 00:00:00 CET 1980
This is the result that you want, correct?

Converting Date to LocalDate returning strange results around 200AD

I'm getting inconsistent results when converting Dates to LocalDates, around the year 200. Using the following code to do the conversion:
private LocalDate toLocalDate(Date localDate)
{
return LocalDateTime.ofInstant(localDate.toInstant(), ZoneId.systemDefault()).toLocalDate();
}
My ZoneId.systemDefault() is Africa/Harare, which matches the CAT used in the test. The test case I run is
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy", Locale.US);
String dateString = "Tue Jan 01 00:00:00 CAT 200";
String dateString2 = "Tue Jan 01 00:00:00 CAT 201";
String dateString3 = "Wed Dec 31 00:00:00 CAT 200";
System.out.println(toLocalDate(simpleDateFormat.parse(dateString)));
System.out.println(toLocalDate(simpleDateFormat.parse(dateString2)));
System.out.println(toLocalDate(simpleDateFormat.parse(dateString3)));
My expected output for this would be
0200-01-01
0201-01-01
0200-12-31
Or, if not that, at least consistently incorrect values. The actual results are
0199-12-31
0201-01-01
0200-12-31
So it seems that the first one is being rolled back slightly, possibly the two hours corresponding to the CAT timezone? But why does this only happen on the one case? Doing the same experiment with the year 2000 does not produce the same error.

Stephen has provided an explanation in the comment. Basically, java.util.Date uses a calendar system which cuts over between the Julian calendar system and the Gregorian calendar system in 1582, skipping 10 days. So dates in 1582 or before will exhibit discrepancies - but the size of the discrepancy will vary over time - by 3 days every 400 years, on average. It so happens that between 200 and 400AD, you don't see this because that corresponds to when the discrepancy is 0.
Here's a short but complete program to demonstrate the problem:
import java.time.*;
import java.util.*;
public class Test {
public static void main(String[] args) throws Exception {
// Value obtained with Noda Time: should be 0199-12-31T22:00:00Z.
long millis = -55855792800000L;
Instant instant = Instant.ofEpochMilli(millis);
Date date = new Date(millis);
System.out.println(instant);
System.out.println(date);
}
}
Output on my machine:
0199-12-31T22:00:00Z
Tue Jan 01 22:00:00 GMT 200
This is all complicated by the problems in your initial code of assuming CAT and Africa/Harare are the same (at that point in time, Africa/Harare is regarded as having an offset of +02:10) and the incorrect day names in your strings - but it's the bug in Java which is causing the issue here.
I suggest you perform all your parsing using the java.time.format classes - then I'd hope you won't get this inconsistency.

Grab exact date without timezone interfering with XMLGregorianCalendar in Java

I have a XMLGregorianCalendar that I would like to convert to a Java Date object, but when I try to covert this:
2013-11-19T00:00:00-00:00
I always get a date with the value a day behind.
Mon Nov 18 17:00:00 MST 2013
I just want a date object containing 11/19/2013.

As commented above, the result you're getting is right - it's the same moment in time. Midnight UTC is 5PM MST the day before. Perhaps you should look into why your time is in "-00:00" instead of "-07:00" (MST)... but in the meanwhile, I suppose you could try this:
public static void main(String... args) throws DatatypeConfigurationException {
XMLGregorianCalendar xcal = DatatypeFactory.newInstance().newXMLGregorianCalendar("2013-11-19T00:00:00-00:00");
Calendar c = xcal.toGregorianCalendar();
c.setTimeZone(TimeZone.getDefault());
Date d = c.getTime();
System.out.println(d);
}
prints out Tue Nov 19 00:00:00 EST 2013, and will work for other times of day, not just midnight.

I just did this,
Date startDate = new Date(request.getStartTime().getYear(), request.getStartTime().getMonth(), request.getStartTime().getDay(), 0, 0, 0);

joda + how can we override epoch date with todays date

I have a requirement, where I need to override the date
when I parse time(hh:mm:ss) using SimpleDateFormat, what i get is object of date (Thu Jan 01 hh:mm:ss IST 1970)
i want to overide epoch date with today date(without time).
is there a api or method in joda/jdk, which can do this for me

Basically, you can't, but what you can do, is merge the values from the "time" conversion with another date (like today)...for example
try {
Date date = new SimpleDateFormat("hh:mm:ss").parse("13:30:51");
System.out.println(date);
Calendar time = Calendar.getInstance();
time.setTime(date);
Calendar today = Calendar.getInstance();
today.set(Calendar.HOUR_OF_DAY, time.get(Calendar.HOUR_OF_DAY));
today.set(Calendar.MINUTE, time.get(Calendar.MINUTE));
today.set(Calendar.SECOND, time.get(Calendar.SECOND));
System.out.println(today.getTime());
} catch (ParseException ex) {
ex.printStackTrace();
}
There's probably a really fancy way of doing this with less code, but I was trying to avoid deprecated methods.
For me, this outputs...
Thu Jan 01 13:30:51 EST 1970
Thu Oct 31 13:30:51 EST 2013
Beware though, this does not reset the milliseconds value of the today Calendar, in case that's important...

Joda Time Not getting expected result

I have a date string of format MM/dd/yyyy that I am parsing using SimpleDateFormat
Now say the startDateString is 11/26/2012 for the code given below. I set the time zone to America/New_York
SimpleDateFormat df=new SimpleDateFormat("MM/dd/yyyy");
Date st = df.parse(startDateString);
Calendar startDate = Calendar.getInstance(TimeZone.getTimeZone("America/New_York"));
System.out.println("BEFORE : Start Date :"+startDate.getTime());
startDate.setTime(st);
System.out.println("AFTER : Start Date :"+startDate.getTime());
DateTimeZone timezone = DateTimeZone.forID("America/New_York");
DateTime actualStartDate = new DateTime(startDate,timezone);
System.out.println("JODA DATE TIME "+ actualStartDate);
The outout of above code snippet:
BEFORE : Start Date :Tue Nov 27 12:26:51 IST 2012
AFTER : Start Date :Mon Nov 26 00:00:00 IST 2012 //ok it sets date to 26th
//with all time parameters as 0.
JODA DATE TIME 2012-11-25T13:30:00.000-05:00 // here the date and
// time parameter are changed
What my problem is when I create my actualStartDate like this :
DateTime actualStartDate = new DateTime(startDate,timezone);
The date changes to 25 and the time changes to 13:00:00
I think this is because of timezone zone difference between India and US (total -10:30 from IST Indian time)
What I want is JODA DATE TIME 2012-11-26T00:00:00.000-05:00
Do I manually set the parameters of time inside my startDate calendar instance to 0 ?

I suspect the problem is that you're parsing in your default time zone. This:
AFTER : Start Date :Mon Nov 26 00:00:00 IST 2012
shows that the instant in time you're using is midnight IST - not midnight in New York or in UTC. Currently IST is 18:30 in UTC, so the instant you're representing is 25-11-25T18:30:00Z.
When you convert that into New York time, you end up with 2012-11-25T13:30:00-05:00, which is exactly what Joda Time is doing.
I would strongly advise that:
You avoid using the Java libraries at all (that's where all the problems have come from here - both in parsing, and the result of Date.toString() confusing you)
You use LocalDate to represent a date, rather than DateTime. You're trying to represent a date after all, not an instant in time. This bypasses time zones entirely, as a date doesn't have a time zone.
Sample code:
import java.util.*;
import org.joda.time.*;
import org.joda.time.format.*;
public class Test {
public static void main (String[] args) {
String text = "11/26/2012";
DateTimeFormatter formatter =
DateTimeFormat.forPattern("MM/dd/yyyy")
.withLocale(Locale.US);
LocalDate date = formatter.parseLocalDate(text);
System.out.println(date);
}
}
Once you've got a LocalDate, if you want to find out the instant at which that day started in a particular time zone, you can use LocalDate.toDateTimeAtStartOfDay(DateTimeZone).