Java date parsing has stranger behavior where parsing different date in different timezone

Question

Here I am trying to parse two dates in java. Date 1 is "2021-01-01" and date 2 is "2021-04-01". But after parsing Java generating Date object with a different timezone. Really confused by this behavior. I am looking at the same timezone and that is EDT.

import java.text.DateFormat;
    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.Locale;
    
    
    public class DateCalculation {
    
        private static final DateFormat formater = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
    
        public static void main(String args[]) throws ParseException {
            Date date1 = getDateFromString("2021-01-01");
            System.out.println("Date 1: " + date1);
    
            Date date2 = getDateFromString("2021-04-01");
            System.out.println("Date 2: " + date2);
        }
    
        public static Date getDateFromString(String dateString) throws ParseException {
            if(dateString == null || dateString.trim().length() == 0)
                return null;
    
            dateString = dateString.replace("\"", ""); // Remove quotes
            return formater.parse(dateString);
        }
    }


Output:
Date 1: Fri Jan 01 00:00:00 EST 2021
Date 2: Thu Apr 01 00:00:00 EDT 2021

Also, remember, Date#toString is using an internal formatter, oh, and you should be using the java.time API over the older java.util based date classes — MadProgrammer
– MadProgrammer, Commented May 2, 2022 at 23:50
I think I understand your confusion. And I don’t think it’s documented behaviour, but this is as confusing the old Date class was behaving (and SimpleDateFormat was even worse). I say ‘was’ because the good solution, really the only sensible solution is to stop using those classes and switch to java.time, the modern Java date and time API. Date and related classes are long outdated. — Anonymous
– Anonymous, Commented May 3, 2022 at 1:40

Basil Bourque · Accepted Answer · 2022-05-03 00:36:05Z

2

You are using terrible date-time classes that were years ago supplanted by the modern java.time classes defined in JSR 310.

`LocalDate`

For a date-only value without time-of-day and without time zone, use LocalDate class.

LocalDate.parse( "2021-04-01" )

`ZonedDateTime`

If you want to represent the first moment of the day for that date in a particular time zone, apply ZoneId to get a ZonedDateTime.

Do not assume the day starts at 00:00:00 🕛. Some dates in some zones start at another time such as 01:00:00 🕐. So let java.time determine the first moment.

EDT is not a real time zone. Perhaps you meant America/Montreal, America/New_York, America/Indiana/Marengo, or some such.

LocalDate ld = LocalDate.parse( "2022-01-23" ) ;
ZoneId z = ZoneId.of( "America/Indiana/Marengo" ) ;
ZonedDateTime zdt = ld.atStartOfDay( z ) ;

edited May 3, 2022 at 0:36

answered May 3, 2022 at 0:22

Basil Bourque

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Java date parsing has stranger behavior where parsing different date in different timezone

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`LocalDate`

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`LocalDate`

`ZonedDateTime`