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

Here is an example that will not work. The condition in the loop will never be satisfied, because the roll, once reaching January 31, 2014, will go back to January 1, 2014.

    Calendar start=new GregorianCalendar();
    start.set(Calendar.YEAR, 2014);
    start.set(Calendar.MONTH, 0);
    start.set(Calendar.DAY_OF_MONTH, 1);
    //January 2, 2014

    Calendar end=new GregorianCalendar();
    end.set(Calendar.YEAR, 2014);
    end.set(Calendar.MONTH, 1);
    end.set(Calendar.DAY_OF_MONTH, 2);
    //February 2, 2014

    while (start.getTime().before(end.getTime())){
        start.roll(Calendar.DATE, 1);
    }