Difference, in minutes, between two dates

Question

I need to get the number of minutes between two dates. I know Joda is the best to use, but this is for an Android project, so I prefer to use a little external libraries as possible, and the app I'm building doesn't require the calculation to be surgically precise.

However, the code I'm using doesn't seem to be working. I'm trying to get the number of minutes between "11/21/2011 7:00:00 AM" and "11/21/2011 1:00:00 PM" (which should be 360 minutes), but the code I'm using returns 0:

int diff = minutesDiff(GetItemDate("11/21/2011 7:00:00 AM"), GetItemDate("11/21/2011 1:00:00 PM"));

public static Date GetItemDate(final String date)
{
    final Calendar cal = Calendar.getInstance(TimeZone.getDefault());
    final SimpleDateFormat format = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss a");
    format.setCalendar(cal);

    try {
        return format.parse(date);
    } catch (ParseException e) {
        return null;
    }
}

public static int minutesDiff(Date earlierDate, Date laterDate)
{
    if( earlierDate == null || laterDate == null ) return 0;

    return (int)((laterDate.getTime()/60000) - (earlierDate.getTime()/60000));
}

Answer 1

If your GetItemDate is failing for either date, you will get zero. On the catch statement, place a println or debug to output the issue and see if that tells you something.

Also, just as a matter of practice, I'd change:

return (int)((laterDate.getTime()/60000) - (earlierDate.getTime()/60000));

to:

long result = ((laterDate.getTime()/60000) - (earlierDate.getTime()/60000));
return (int) result;

This gives you the opportunity to view the result of the math in an IDE.

Answer 2

I debugged through your code: there is ParseException in GetItemDate() for both of the date strings like:

Unparseable date: 11/21/2011 07:00:00 AM

The problem is that parsing AM/PM hours only works with "hh" (small caps!) or "KK". At least that is the case in my phone (it seems some of us didn't see this issue at all). I tested it also works with a single "h" too.

hh = 1-12
KK = 0-11
HH = 0-23
kk = 1-24

Change your SimpleDateFormat line to this:

final SimpleDateFormat format = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss a", Locale.US);

This post explains the "a" and Locale: Unable to parse DateTime-string with AM/PM marker

PS. I'm from Finland so I must use the "Locale.US" part for this to work. US residents may test the code without it, I think.