Java Calendar 31st January issue

Question

I have the following code :-

        Calendar calc = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("MMM-yyyy");
        calc.set(Calendar.YEAR, calc.get(Calendar.YEAR) - 1);
        calc.set(Calendar.MONTH, Calendar.NOVEMBER);
        System.out.println("---NOV? : " + sdf.format(calc.getTime()));

        Calendar calc1 = Calendar.getInstance();
        calc1.set(Calendar.YEAR, calc1.get(Calendar.YEAR) - 1);
        calc1.set(Calendar.MONTH, Calendar.DECEMBER);
        System.out.println("-- DEC : " + sdf.format(calc1.getTime()));

The output of the above code is :-

> ---NOV? : Dec-2012
> -- DEC : Dec-2012

This happens only for 31st january, can someone explain why this might be happening?

Answer 1

The Calendar is set for lenient interpretation, so if you tell it the 31st day of November, well, November only has 30 days, so it rolls over to December 1st.