Adds or subtracts the specified amount of time to the given calendar field, based on the calendar's rules. For example, to subtract 5 days from the current time of the calendar, you can achieve it by calling:

add(Calendar.DAY_OF_MONTH, -5).

Parameters:

field		the calendar field.
amount		the amount of date or time to be added to the field.

See also:
roll(int,int), set(int,int)