Days difference in dates in java giving wrong output

Question

Hi i am trying to calculate difference of two dates in days. The dates are 14 of this month and today. It should be 2. But o/p is 0 always. Code:

    long today = (new java.util.Date().getTime());
    long difference =(long) (today - 1394809789186.0);
    long daysdifference = difference/(24*3600*1000);
    System.out.println(daysdifference);

o/p: 0.

whats wrong?

Now i did another trick and it gives perfect answer dont know whats wrong with above code...

   SimpleDateFormat df = new SimpleDateFormat("dd.mm.yyyy"); 
    long firstdateseconds = df.parse("14.03.2014").getTime();
    long today = df.parse("16.03.2014").getTime();
    long difference = (today-firstdateseconds);
    long days = (long)(difference/(24*3600*1000));
    System.out.println(days);

o/p : 2 // now correct bingo!

Guys whats happening?

You should try printing out intermediate values to see what's going on. Also, what is the magic number `1394809789186.0`? — Oliver Charlesworth, Mar 16 '14 at 15:19
@oli: it's a millisecond timestamp that corresponds to Mar 14th. — Marc B, Mar 16 '14 at 15:19
@MarcB: Yeah, I assumed that ;) But I'm wondering why the OP has that hardcoded, rather than simply explicitly constructing it as such. — Oliver Charlesworth, Mar 16 '14 at 15:21
If you used the [Joda-Time](http://www.joda.org/joda-time/) API, you would never have to worry about such calculations. — Tiny, Mar 16 '14 at 15:39
Regarding your edit; did you think to print out the values of `firstdateseconds` and `today`, and see how they correspond to your magic hard-coded number? — Oliver Charlesworth, Mar 16 '14 at 15:50
I dont know why people just downvote instead of directly showing the mistakes. — Deepsthecoder, Mar 16 '14 at 16:06
@ Tiny, I beleive in Java se7 developers and my brain and people here helping others, more than the joda..whatever API. — Deepsthecoder, Mar 16 '14 at 16:13
See [this answer](http://stackoverflow.com/a/3802949/642706) for a simple one-liner using the [Joda-Time](http://www.joda.org/joda-time/) library: `Days.daysBetween(start.withTimeAtStartOfDay() , end.withTimeAtStartOfDay() ).getDays()` — Basil Bourque, Mar 16 '14 at 20:48

Crystal Meth · Answer 1 · 2014-03-16T16:22:04.127

0

I used the following simple code to accomplish what you want:

import java.util.Date;

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

        Date d1 = new Date();
        Date d2 = new Date(2014 - 1900, 2, 14);
        long d1_millis = d1.getTime();
        long d2_millis = d2.getTime();
        long diffMillis = d1_millis - d2_millis;
        long diffDays = diffMillis / (24 * 3600 * 1000);
        System.out.println("Difference in days: " + diffDays);

    }
}

OUTPUT:

Difference in days: 2

Also note that the magic number that you are using while calculating the difference is incorrect.

The actual value to subtract is : 1394735400000

That is the most dangerous disadvantage of using magic numbers.

Hope that clarifies things for you.

edited Mar 16 '14 at 16:22

answered Mar 16 '14 at 15:33

Crystal Meth

589
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4
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Please check the ranges of the inputs to the `Date` constructor in the Javadoc... – Oliver Charlesworth Mar 16 '14 at 15:35
I have simplified the code and also given the output. – Crystal Meth Mar 16 '14 at 16:16

Peter Keller · Answer 2 · 2014-03-16T20:28:04.053

Perhaps a combined TimeZone and "Time (hours/minutes/seconds)" issue?

Case I

Different timezones and different day times:

 public static void main(final String[] args) {

    final Calendar march14 = Calendar.getInstance(TimeZone.getTimeZone("US/Hawaii"));
    march14.set(2014, Calendar.MARCH, 14, 23, 59, 0);

    final Calendar march16 = Calendar.getInstance(TimeZone.getTimeZone("Asia/Tokyo"));
    march16.set(2014, Calendar.MARCH, 16, 0, 0, 0);

    final long diffInMs = march16.getTimeInMillis() - march14.getTimeInMillis();
    System.out.println("diff = " + diffInMs / (24 * 3600 * 1000)+" day(s)");

}

This prints:

diff = 0 day(s)

Case II

However, adjusting the time zone:

public static void main(final String[] args) {

    final Calendar march14 = Calendar.getInstance(TimeZone.getTimeZone("US/Hawaii"));
    march14.set(2014, Calendar.MARCH, 14, 23, 59, 0);

    final Calendar march16 = Calendar.getInstance(TimeZone.getTimeZone("US/Hawaii")); // <- CHANGE!
    march16.set(2014, Calendar.MARCH, 16, 0, 0, 0);

    final long diffInMs = march16.getTimeInMillis() - march14.getTimeInMillis();
    System.out.println("diff = " + diffInMs / (24 * 3600 * 1000)+" day(s)");

}

This prints:

diff = 1 day(s)

Case III

And adjusting the time (hours/minutes/seconds):

public static void main(final String[] args) {

    final Calendar march14 = Calendar.getInstance(TimeZone.getTimeZone("US/Hawaii"));
    march14.set(2014, Calendar.MARCH, 14, 0, 0, 0);  // <- CHANGE!

    final Calendar march16 = Calendar.getInstance(TimeZone.getTimeZone("US/Hawaii"));
    march16.set(2014, Calendar.MARCH, 16, 0, 0, 0);

    final long diffInMs = march16.getTimeInMillis() - march14.getTimeInMillis();
    System.out.println("diff = " + diffInMs / (24 * 3600 * 1000)+" day(s)");

}

This prints:

diff = 2 day(s)

Conclusions

My two advices:

Don't use magic numbers, set all parts of your date/calendar objects that are relevant
Always set the TimeZone when working with date/time

Additional note to SimpleDateFormat

By the way: In SimpleDateFormat m is for minutes, M for month in year, see http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html. It was pure random that the result of your calculations was 2.

score -1 · Answer 3 · answered Mar 16 '14 at 15:19

-1

Use double you are crossing a truncation issue

answered Mar 16 '14 at 15:19

venergiac

7,469
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Use `double` for what? – Oliver Charlesworth Mar 16 '14 at 15:19
Now did this: long today = (new java.util.Date().getTime()); double difference =(double) (today - 1394809789186.0); double daysdifference = difference/(24*3600*1000); o/p : 0.008885162037037037 – Deepsthecoder Mar 16 '14 at 15:23
When i use long it says number too long in netbeans.. so used double – Deepsthecoder Mar 16 '14 at 15:24
Because there is a division and it truncates to 0 if one day is not elapsed. – venergiac Mar 16 '14 at 17:54

Days difference in dates in java giving wrong output

3 Answers3