Calculate number of days between today and my next birthday - android-studio

Question

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 :)

Answer 1

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
Oracle tutorial: Date Time explaining how to use java.time.
Java Specification Request (JSR) 310, where java.time was first described.
ThreeTen Backport project, the backport of java.time to Java 6 and 7 (ThreeTen for JSR-310).
ThreeTenABP, Android edition of ThreeTen Backport
Question: How to use ThreeTenABP in Android Project, with a very thorough explanation.

Answer 2

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;
}
}