Remaining Days To A Date Is Not Showing Correctly

May 09, 2023 Post a Comment

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 ran

Solution 1:

java.time

java.time, the modern Java date and time API, has methods for calculating the number of days between two dates. So don’t bother doing this calculation yourself. It’s error-prone.

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("dd-MM-uuuu H:mm");
    String inputDateString = "01-10-2018 23:59";
    LocalDate today = LocalDate.now(ZoneId.of("Pacific/Auckland"));
    LocalDate expiration = LocalDate.parse(inputDateString, dateFormatter);
    if (expiration.isAfter(today)) {
        String numberOfDays = "Days left: " + ChronoUnit.DAYS.between(today, expiration);
        System.out.println(numberOfDays);
    }

Running this snippet just now (already September 13 in New Zealand) I got this output:

Days left: 18

Please substitute your correct time zone if it didn’t happen to be Pacific/Auckland.

The answer by LaVepe has already explained nicely and correctly what went wrong in your code, so I am not repeating that.

The date and time classes you were using — Calendar and SimpleDateFormat — are long outdated and were always poorly designed. There is a way to get Calendar to count days, 1 day at a time, but it’s not well suited for that. SimpleDateFormat is notorious for the trouble it has caused for many programmers. I recommend you avoid those classes altogether and use java.time instead.

Question: Can I use java.time on Android?

Yes, java.time works nicely on older and newer Android devices. It just requires at least Java 6.

In Java 8 and later and on newer Android devices (from API level 26, I’m told) the modern API comes built-in.
In Java 6 and 7 get the ThreeTen Backport, the backport of the new classes (ThreeTen for JSR 310; see the links at the bottom).
On (older) Android use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. And make sure you import the date and time classes from org.threeten.bp with subpackages.

Solution 2:

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)

Solution 3:

To get interval days between two days, you could do like this:

public long daysTillExpire() {

    SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
    String dateInString = "01-10-2018 23:59";
    Date date = null;
    try {
        date = sdf.parse(dateInString);
    } catch (ParseException e) {
        e.printStackTrace();
    }

    Calendar expiredCalendar = Calendar.getInstance();
    expiredCalendar.setTime(date);

    long msDiff = expiredCalendar.getTimeInMillis() - Calendar.getInstance().getTimeInMillis();
    long daysDiff = TimeUnit.MILLISECONDS.toDays(msDiff); 

    return daysDiff;
}

above function is tested successfully, modify it according to your requirment.

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