Subtracting a date from the current day in Java

I have a particular date format.I can subtract 2 dates but I can't achieve to subtract today's date from a future one.

I found the way to get today's date

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/yyyy");
	LocalDateTime now = LocalDateTime.now();
	System.out.println(dtf.format(now));

Here is the way I subtract 2 dates(Strings)

public boolean DateDiff(String datep,String dater) {
		DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
		LocalDate date1 = LocalDate.parse(datep, formatter);
		LocalDate date2 = LocalDate.parse(dater, formatter);
		
		long elapsedDays = ChronoUnit.DAYS.between(date1, date2);

I can't turn the current day to a String so I can have 2 same types of variables to subtract.What kind of type is the LocalDateTime now

To subtract dates is as easy as this one using the minusDays() function of LocalDate:

LocalDate now = LocalDate.now();
LocalDate thirtyDaysAgo = now.minusDays(30);

If you have a standard string of date, see "2020-08-27", you can parse it this way:

String date = "2020-08-27";
LocalDate thirtyDaysAgo = LocalDate.parse(date).minusDays(30);
System.out.println(thirtyDaysAgo); //prints 2020-07-28

If you have a special format of date, see "2020/08/27", you parse it this way:

String date = "2020/08/27";
LocalDate thirtyDaysAgo = LocalDate.parse(date, DateTimeFormatter.ofPattern("yyyy/MM/dd")).minusDays(30);
System.out.println(thirtyDaysAgo); //prints 2020-07-28

To turn a LocalDate to a String with format, you do it this way:

LocalDate date = LocalDate.now();
String formatedDate = date.format(DateTimeFormatter.ofPattern("yyyy/MM/dd"));
System.out.println(formatedDate); //prints 2020/08/27

Use LocalDate instead of LocalDateTime to get today's date

LocalDate currentDate = LocalDate.now();

For some reason if you still want to use LocalDateTime to get today's date, this is how you can do it

LocalDateTime currentDateTime = LocalDateTime.now();
LocalDate currentDate = currentDateTime.toLocalDate();

if you want to convert currentDate to String in your desired format as follows:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");   
String currentDateString = currentDate.format(formatter);

if both the dates you have are of type LocalDate, then you can find the number of days in between them as follows:

public long DateDiff(LocalDate date1,LocalDate date2) {

    return Duration.between(date1, date2).toDays();
}

if both the dates you have are of type String, then you can find the number of days in between them as follows:

public long DateDiff(String dateString1,String dateString2) {

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
    LocalDate date1 = LocalDate.parse(dateString1, formatter);
    LocalDate date2 = LocalDate.parse(dateString2, formatter);

   return Duration.between(date1, date2).toDays();
}

Hope that solves your problem

You can use joda-time library its a bliss when working with dates in java.

Subtract 2 dates

DateTime yesterday = new DateTime().withTimeAtStartOfDay().minusMinutes(10);

DateTime twoDaysFromToday = new DateTime().withTimeAtStartOfDay().plusDays(2);

Days.daysBetween(yesterday.toLocalDate(), twoDaysFromToday.toLocalDate()).getDays();

Use LocalDate (not LocalDateTime).

	DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
	
	LocalDate today = LocalDate.now(ZoneId.of("Asia/Calcutta"));
    LocalDate futureDate = LocalDate.parse("26/09/2020", formatter);
    long elapsedDays = ChronoUnit.DAYS.between(today, futureDate);
    
    System.out.println("Days until future date: " + elapsedDays);

Output was when running just now:

> Days until future date: 29