I tried to calculate the difference between two dates and I noticed one thing. When calculating only the days, the start of daylight saving time is included in the interval,
Oh yes a better solution there is!
Stop using the outmoded java.util.Date
class and embrace the power of the java.time API built into Java 8 and later (tutorial). Specifically, the DateTimeFormatter, LocalDate, and ChronoUnit classes.
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM-dd-yyyy");
LocalDate date1 = LocalDate.parse("03-29-2015", formatter);
LocalDate date2 = LocalDate.parse("03-30-2015", formatter);
long days = ChronoUnit.DAYS.between(date1, date2);
System.out.println(days); // prints 1