How to get the the number of days between two dates - `java.util.Calendar`

Question

I'm trying to get the number of days between two dates. I'm working from Agenda, JFXtras.

The start time = getStartTime() returns java.util.Calendar
The end time = getEndTime() returns java.util.Calendar

This is what I've got so far:

void printAppointment(Appointment a) throws ParseException {
        System.out.println(a.getSummary());
        System.out.println(a.getDescription());

        DateFormat formatter = new SimpleDateFormat("yyyy, MMM dd h:mm:ss a z");
        System.out.println(formatter.format(a.getStartTime().getTime()));
        System.out.println(formatter.format(a.getEndTime().getTime()));
        System.out.println(a.getAppointmentGroup());
        System.out.println(a.getLocation());

        // My problem starts here
        Calendar cal1 = new GregorianCalendar();
        Calendar cal2 = new GregorianCalendar();

        SimpleDateFormat sdf = new SimpleDateFormat("ddMMyyyy");

        Date date = sdf.parse(formatter.format(a.getStartTime().getTime()));
        cal1.setTime(date);
        date = sdf.parse(formatter.format(a.getEndTime().getTime()));
        cal2.setTime(date);
        // System.out.println("Days difference = " + daysBetween(cal1.getTime(), cal2.getTime()));
        System.out.println("Days difference = can't be set");
    }

    private int daysBetween(Date d1, Date d2) {
        return (int) ((d2.getTime() - d1.getTime()) / (1000 * 60 * 60 * 24));
    }

After // My problem starts here I get nothing. The following gets printed:

Another Morning appointment
Another Description of morning appointment
2014, Jun 12 6:00:00 AM PDT
2014, Jun 13 2:00:00 AM PDT
jfxtras.labs.scene.control.Agenda$AppointmentGroupImpl@16e4577
null

Note that the difference in days gets left out.

If anyone could help me out, I'll be more than greatful. Thank you all.

Update:

This is the final working implementation that does the difference in Days, Hours, Minutes and seconds as the attempt below shows.

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2014. Jun Mon.9 3:18PM
2014. Jun Wed.11 3:18PM
jfxtras.labs.scene.control.Agenda$AppointmentGroupImpl@12e3872
null
diffSeconds difference = 172800
diffMinutes difference = 2880
diffHours difference = 48
diffDays difference = 2

This is the code that does that

void printAppointment(Appointment a) {
    System.out.println(a.getSummary());
    System.out.println(a.getDescription());

    DateFormat formatter = new SimpleDateFormat("yyyy. MMM EEE.d h:mma");
    System.out.println(formatter.format(a.getStartTime().getTime()));
    System.out.println(formatter.format(a.getEndTime().getTime()));
    System.out.println(a.getAppointmentGroup());
    System.out.println(a.getLocation());
    this.daysBetween(a.getStartTime().getTimeInMillis(), a.getEndTime().getTimeInMillis());

}

private void daysBetween(long t1, long t2) {
    int diff = (int) (t2 - t1);

    long diffSeconds = diff / 1000;
    long diffMinutes = diff / (60 * 1000);
    long diffHours = diff / (60 * 60 * 1000);
    long diffDays = diff / (24 * 60 * 60 * 1000);

    System.out.println("diffSeconds difference = " + diffSeconds);
    System.out.println("diffMinutes difference = " + diffMinutes);
    System.out.println("diffHours difference = " + diffHours);
    System.out.println("diffDays difference = " + diffDays);
}

FYI, the troublesome old date-time classes such as [`java.util.Date`](https://docs.oracle.com/javase/9/docs/api/java/util/Date.html), [`java.util.Calendar`](https://docs.oracle.com/javase/9/docs/api/java/util/Calendar.html), and `java.text.SimpleDateFormat` are now [legacy](https://en.wikipedia.org/wiki/Legacy_system), supplanted by the [java.time](https://docs.oracle.com/javase/9/docs/api/java/time/package-summary.html) classes built into Java 8 & Java 9. See [Tutorial by Oracle](https://docs.oracle.com/javase/tutorial/datetime/TOC.html). — Basil Bourque, Feb 09 '18 at 01:21

score 5 · Accepted Answer · edited Apr 02 '15 at 18:30

5

Instead of passing a Date to daysBetween, pass a long. You can get the current time (since Jan 1 1970) from a Calendar using getTimeInMillis(). Your code will now look as follows:

void printAppointment(Appointment a) throws ParseException {
    System.out.println(a.getSummary());
    System.out.println(a.getDescription());

    System.out.println(formatter.format(a.getStartTime().getTime()));
    System.out.println(formatter.format(a.getEndTime().getTime()));
    System.out.println(a.getAppointmentGroup());
    System.out.println(a.getLocation());


    System.out.println("Days difference = " + daysBetween(a.getStartTime().getTimeInMillis(), a.getEndTime().getTimeInMillis()));
}

private int daysBetween(long t1, long t2) {
    return (int) ((t2 - t1) / (1000 * 60 * 60 * 24));
}

edited Apr 02 '15 at 18:30

JodyT

4,324
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answered Jun 08 '14 at 11:11

Simon

1,416
1
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24

Thanks for the help @Simon. I tried it and it works with days. I tried to get the difference in Hours, Minutes and Seconds but was unable. Could you please look at my update above, if you could help please? – user3719487 Jun 08 '14 at 12:04
Your code is working for me. What is the issue you are getting? [The code I'm using](http://pastebin.com/e4SC3c7N). PS the calculation can be simplified by using: long diffSeconds = diff / 1000; long diffMinutes = diffSeconds / 60; long diffHours = diffMinutes / 60; long diffDays = diffHours / 24; – Simon Jun 08 '14 at 12:09
Sorry about that! Did Clean and Build, which refreshed the project. I think my IDE was not taking in new code edits. Thank you a million. – user3719487 Jun 08 '14 at 12:20
Silly IDE's. You're welcome! – Simon Jun 08 '14 at 12:29
@stuart, there are always more things you can [edit with a post](http://stackoverflow.com/review/suggested-edits/7558496), so one-character edits won't cut it. And please don't put edit summaries in the post, that's what the edit summaries are for. – gunr2171 Apr 02 '15 at 18:42

score 1 · Answer 2 · edited May 23 '17 at 12:13

If you are allowed to use Java 8 than you should have a look at the answer from https://stackoverflow.com/users/288671/vitalii-fedorenko for the question Difference in days between two dates in Java?

There are several reasons for the introduction of the new API in Java 8 - the correct handling of time differences was one of those reasons. (In some timezones there might have been changes affecting the calculation - so just dividing the difference in millis will lead to unexpected results if there are daytime adjustments or similar things)

How to get the the number of days between two dates - `java.util.Calendar`

2 Answers2