Calendar add() vs roll() when do we use it?

Question

I know add() adds the specified (signed) amount of time to the given time field, based on the calendar\'s rules.

And roll() adds the specif

Answer 1

• add() - almost always, as you said
• roll() - for example you want to "dispense" events in one month. The algorithm may be to proceed a number of days and place the event, then proceed further. When the end of the month is reached, it should start over from the beginning. Hence roll().