Maybe you don't understand the difference between a Timestamp object and the string representation of a Timestamp object.
A Timestamp object contains a date and time. It does not have a specific format by itself. If you call toString() on a Timestamp, you might get a String that looks like "2006-01-02 00:06:00.0". The toString() method uses a default format, because it has to convert the date and time value into a String somehow. But again, the format itself is not a property of the Timestamp object.
If you want to convert the Timestamp object to a String with a specific format, you need to use the SimpleDateFormat.format(...) method, which allows you to specify a specific format.