Question

For example

DateTime dt=new DateTime(java.sql.Time.valueOf("00:00:00"));
dt.minusMinutes(20); // this line would have no effect!

The problem is that new DateTime set date at “January 1, 1970”

A fix could be setting actual date, then it gives a big range to go backward in time, but I think it’s not the standar way and neither pure hh:mm:ss.

Answer 1

I think you are confusing something here. Everything in JodaTime is immutable, to see an effect you need to re-assign the variable:

DateTime dt = new DateTime(java.sql.Time.valueOf("00:00:00"));
DateTime dt2 = dt.minusMinutes(20); // but this line would have effect!