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Currently i'm working on an android studio project.i need a function which returns number of days between today and my next birthday. i.e,

long daysForBirthday(dob){
   .....
   .....
   return days;
}

I will use the return value to make notifications.

If today is 23/05/2020 and my birth date is 28/05/1999 the function should remain 5. I'm very noob in android studio so please forgive my mistakes. Thank you :)

Shyam Sangeeth
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2 Answers2

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java.time and ThreeTenABP

My suggestion is using java.time, the modern Java date and time API:

public static int daysRemain(LocalDate dob){
    LocalDate today = LocalDate.now(ZoneId.of("Asia/Kolkata"));
    long age = ChronoUnit.YEARS.between(dob, today);
    LocalDate nextBirthday = dob.plusYears(age);
    if (nextBirthday.isBefore(today)) {
        nextBirthday = dob.plusYears(age + 1);
    }
    long daysUntilNextBirthday = ChronoUnit.DAYS.between(today, nextBirthday);
    return Math.toIntExact(daysUntilNextBirthday);
}

Let’s try it out:

    System.out.println(daysRemain(LocalDate.of(1999, Month.MAY, 28)));

When I ran this call today (25th May in India), the output was:

3

Question: Doesn’t java.time require Android API level 26?

java.time works nicely on both 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) the modern API comes built-in.
  • In non-Android Java 6 and 7 get the ThreeTen Backport, the backport of the modern 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.

Links

Ole V.V.
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I think i found an answer. please let me know if there is a problem.

long daysForBirthday(String dob){
        SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy", Locale.getDefault());
        String dateOB=dob.split("/")[0]+"/"+dob.split("/")[1]+"/"+Calendar.getInstance().get(Calendar.YEAR);
        if((Calendar.getInstance().get(Calendar.YEAR)%4!=0)&&(Integer.parseInt(dob.split("/")[0])==29)&&(Integer.parseInt(dob.split("/")[1])==2)){
            dateOB="01/03/"+Calendar.getInstance().get(Calendar.YEAR);
        }
        try {
            Date bday=format.parse(dateOB);
            Date today=Calendar.getInstance().getTime();
            assert bday!=null;
            if(bday.before(today)){
                Calendar c=Calendar.getInstance();
                c.setTime(bday);
                c.add(Calendar.YEAR,1);
                bday=new Date(c.getTimeInMillis());
            }
            return TimeUnit.DAYS.convert(bday.getTime()-today.getTime(),TimeUnit.MILLISECONDS);
        } catch (ParseException e) {
            e.printStackTrace();
            return -1;
        }
    }
Shyam Sangeeth
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    Consider throwing away the long outmoded and notoriously troublesome `SimpleDateFormat` and friends, and adding [ThreeTenABP](https://github.com/JakeWharton/ThreeTenABP) to your Android project in order to use java.time, the modern Java date and time API. It is so much nicer to work with. I called `daysForBirthday("28/05/1999")` today, 25th May in India, and got 2, I don’t know why. – Ole V.V. May 24 '20 at 18:36
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    I think the reason why it gives one day too few is that it measures time from this moment to the start of the birthday and rounds down to a whole number of days. You would have wanted to count from the start of today’s date or round up rather than down. So I think. – Ole V.V. May 24 '20 at 18:47
  • I think it is excluding the date 25/05/2020 – Shyam Sangeeth May 24 '20 at 18:51