Calculating days between two dates with Java

Question

I want a Java program that calculates days between two dates.

1. Type the first date (German notation; with whitespaces: \"dd mm yyyy\")
2. Type the second

Answer 1

UPDATE: The original answer from 2013 is now outdated because some of the classes have been replaced. The new way of doing this is using the new java.time classes.

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd MM yyyy");
String inputString1 = "23 01 1997";
String inputString2 = "27 04 1997";

try {
    LocalDateTime date1 = LocalDate.parse(inputString1, dtf);
    LocalDateTime date2 = LocalDate.parse(inputString2, dtf);
    long daysBetween = Duration.between(date1, date2).toDays();
    System.out.println ("Days: " + daysBetween);
} catch (ParseException e) {
    e.printStackTrace();
}

Note that this solution will give the number of actual 24 hour-days, not the number of calendar days. For the latter, use

long daysBetween = ChronoUnit.DAYS.between(date1, date2)

---

Original answer (outdated as of Java 8)

You are making some conversions with your Strings that are not necessary. There is a SimpleDateFormat class for it - try this:

SimpleDateFormat myFormat = new SimpleDateFormat("dd MM yyyy");
String inputString1 = "23 01 1997";
String inputString2 = "27 04 1997";

try {
    Date date1 = myFormat.parse(inputString1);
    Date date2 = myFormat.parse(inputString2);
    long diff = date2.getTime() - date1.getTime();
    System.out.println ("Days: " + TimeUnit.DAYS.convert(diff, TimeUnit.MILLISECONDS));
} catch (ParseException e) {
    e.printStackTrace();
}

EDIT: Since there have been some discussions regarding the correctness of this code: it does indeed take care of leap years. However, the TimeUnit.DAYS.convert function loses precision since milliseconds are converted to days (see the linked doc for more info). If this is a problem, diff can also be converted by hand:

float days = (diff / (1000*60*60*24));

Note that this is a float value, not necessarily an int.