Calculating date and time duration (in hours, and days and hours)

You can use Java built-in class, TimeUnit.

Date startDate = // Set start date
Date endDate   = // Set end date

long duration  = endDate.getTime() - startDate.getTime();

long diffInSeconds = TimeUnit.MILLISECONDS.toSeconds(duration);
long diffInMinutes = TimeUnit.MILLISECONDS.toMinutes(duration);
long diffInHours = TimeUnit.MILLISECONDS.toHours(duration);
long diffInDays = TimeUnit.MILLISECONDS.toDays(duration);

If you have dates in string format then convert to date and use above logic to find difference in days, hour, minutes etc.

String start = "01/04/22 08:19:51";
String stop = "16/08/22 07:23:54";

SimpleDateFormat format = new SimpleDateFormat("yy/MM/dd HH:mm:ss");  

Date startDate = null;
Date endDate = null;
try {
    startDate = format.parse(start);
    endDate = format.parse(stop);
}catch(ParseException ex){
ex.printStackTrace();
}
long duration  = endDate.getTime() - startDate.getTime();

 Hope this helps!

Hello @daniel_claire 

I would prefer to use suggested java.util.concurrent.TimeUnit [1] class.

String dateStart = "01/03/22 09:29:58";
String dateStop = "11/07/22 09:33:43";

// Custom date format
SimpleDateFormat format = new SimpleDateFormat("yy/MM/dd HH:mm:ss");  

Date d1 = null;
Date d2 = null;
try {
    d1 = format.parse(dateStart);
    d2 = format.parse(dateStop);

    long diff = d2.getTime() - d1.getTime();
    long seconds = TimeUnit.MILLISECONDS.toSeconds(diff);
    long minutes = TimeUnit.MILLISECONDS.toMinutes(diff); 
    long hours = TimeUnit.MILLISECONDS.toHours(diff); 
    long days = TimeUnit.MILLISECONDS.toDays(diff); 

} catch (ParseException e) {
    e.printStackTrace();
}    

Also, see other discussions on the same [2] [3]

[1] https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html

[2] https://stackoverflow.com/questions/15540801/time-difference-program/15541322#15541322 

[3] https://stackoverflow.com/questions/625433/how-to-convert-milliseconds-to-x-mins-x-seconds-in-java