Remaining days to a date is not showing correctly

Question

Ok, so I've created a function to show the number of days until a date in the future... It is correct until the amount of days is over 9 days.. if over it seems to show a random number of days... Please see my code below:

   public String daysTillExpire() {
        String daysLeft = "";
        int position = 0 ;
        String inputDateString = UIDM.get(position).date;
        Calendar calCurr = Calendar.getInstance();
        Calendar day = Calendar.getInstance();


        try {
            day.setTime(new SimpleDateFormat("dd-MM-yyyy").parse(inputDateString));

        } catch (ParseException e) {
            e.printStackTrace();
        }

            if (day.after(calCurr)) {

                String noumberOfDays = "Days left: " + (day.get(Calendar.DAY_OF_MONTH) - (calCurr.get(Calendar.DAY_OF_MONTH)));

                daysLeft = UIDM.get(position).date + "\n(" + noumberOfDays+")" ;

            }

            else if (day.before(calCurr)) {
                daysLeft = "Key Expired";
            return daysLeft; }
        return daysLeft;
    }

UIDM is a data model containing info... String inputDateString = UIDM.get(position).date; returns the value 01-10-2018 23:59.

Answer 1

Note that Calendar.DAY_OF_MONTH returns the day of the month between 1 and 31

so it will calculate difference between two days (number between 1 and 31) as if they were in the same month

I would suggest to rather use timestamps and then convert the result from millis to number of days like this:

long oneDay = 24 * 60 * 60 * 1000;  // in milliseconds
long diff = day.getTime().getTime() - calCurr.getTime().getTime();
long numberOfDays = diff / oneDay;

then you can change it to String with Long.toString(numberOfDays)