The problem is that because of Daylight Saving Time shift (on Sunday, March 8, 2020), there are 28 days and 23 hours between those dates. TimeUnit.DAYS.convert(...)
truncates the result to 28 days.
To see the problem (I’m in US Eastern time zone):
SimpleDateFormat fmt = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
long diff = fmt.parse("30-03-2020 00:00:00").getTime() -
fmt.parse("1-03-2020 00:00:00").getTime();
System.out.println(diff);
System.out.println("Days: " + TimeUnit.DAYS.convert(Math.abs(diff), TimeUnit.MILLISECONDS));
System.out.println("Hours: " + TimeUnit.HOURS.convert(Math.abs(diff), TimeUnit.MILLISECONDS));
System.out.println("Days: " + TimeUnit.HOURS.convert(Math.abs(diff), TimeUnit.MILLISECONDS) / 24.0);
Output
2502000000
Days: 28
Hours: 695
Days: 28.958333333333332
To fix, use a time zone that doesn’t have DST, e.g. UTC:
SimpleDateFormat fmt = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
fmt.setTimeZone(TimeZone.getTimeZone("UTC"));
long diff = fmt.parse("30-03-2020 00:00:00").getTime() -
fmt.parse("1-03-2020 00:00:00").getTime();
Output
2505600000
Days: 29
Hours: 696
Days: 29.0