Convert date to long (manually)

Question

I want to convert a date to a long value (that is the milliseconds)

I have a date like

2/11/2014

I want to calculate the date in long (manual)

What I've tried

(2014 - 1970 ) * 31449600000 + 11 * 2592000000 + 2 * 604800000

This equals 1413504000000.

But http://www.fileformat.info/tip/java/date2millis.htm tells me that 1413504000000 is

Date (America/New_York) Thursday, October 16, 2014 8:00:00 PM EDT
Date (GMT)  Friday, October 17, 2014 12:00:00 AM GMT
Date (short/short format)   10/16/14 8:00 PM

Where I'm wrong?

Again, I want to do this manually, not using java code.

@Keppil Good point. Do you have any ideea how can I change my 'formula' ? — Boldijar Paul, Nov 05 '14 at 14:56
And while we're on the subject of leap years, you also can't assume every 4th year is a leap year. 2000 is a leap year, but 2100, 2200, and 2300 are not, even though they are %4. — Compass, Nov 05 '14 at 14:57
Leap year, That is what you didnt consider! Also some month are 30 days some arent — Lrrr, Nov 05 '14 at 14:57
You can loop through the years and check. All years divisible by 4 are leap years, except the ones divisible by 100, but including the ones divisible by 400. So, every 4 years in your range should be a leap year unless you are using dates from later than 2099. — Keppil, Nov 05 '14 at 14:57
Even if you don't want to use java code, you can look into it: http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/Date.java#Date.%3Cinit%3E%28int%2Cint%2Cint%2Cint%2Cint%2Cint%29 — msrd0, Nov 05 '14 at 14:58
Some cases are even weirder than leap years: http://stackoverflow.com/a/11221765/2136410 and http://stackoverflow.com/a/6841479/2136410 — Fabinout, Nov 05 '14 at 15:02
@Sizik Well. I'm using Odata, and I have the birthdate of a field in DateTime, and I need to calculate the age of the field in the URL .. there I can only use + * - / % ... , no 'if', no 'for' etc..Maybe I'll change the way I'm trying to do this right now.. — Boldijar Paul, Nov 05 '14 at 15:20

score 2 · Answer 1 · answered Nov 05 '14 at 15:40

Do not re-invent the wheel. Time/date calculations are notoriously difficult, even standard java library does not get it right. Use JodaTime:

import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

public class JodaTimeSample {

  public static void main(String[] args) {
    DateTimeFormatter formatter = DateTimeFormat.forPattern("dd/MM/yyyy");
    DateTime date = DateTime.parse("2/11/2014", formatter);
    System.out.println("Date: " + date.toString());
    System.out.println("Millis: " + date.getMillis());
  }
}

1ac0 · Answer 2 · 2014-11-05T15:58:19.977

0

If you are sure you could do it manually (huh, why? - looks like homework), open JodaTime source code and copy it. You won't invent it better. Or even better open, read and then try to write it in your editor.

edited Nov 05 '14 at 15:58

answered Nov 05 '14 at 15:49

1ac0

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3
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score 0 · Answer 3 · answered Jun 02 '16 at 17:31

why you do manually to convert date into long or long into date, write a simple java code which give you correct results after convention, I am using the simple programme and convert it as per my user

public class test {

    public static void main(String[] args) {

            Date dt=new Date(Long.valueOf(1390973400983L));
            System.out.println(dt.toString());

            Calendar cal=Calendar.getInstance();
            cal.set(2014, Calendar.JANUARY, 29, 11, 00, 0);

            System.out.println(cal.getTimeInMillis());
            System.out.println();

    }

}

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Convert date to long (manually)

3 Answers3