如何计算一个月内的天数？用户输入当月号

Question

如何计算一个月内的天数？用户输入当月号。 我为上面写了一段代码，想知道它是否合适。

public class Exercise{


    public static void main(String[] args) {

        System.out.print("Input a month number:");
        Scanner scan ;
        int month = 1; int monthName = 1;
        while(month < 12 && month > 0) {
            scan = new Scanner(System.in);
            monthName = scan.nextInt();

            month= monthName-1;
            DateFormat df = new SimpleDateFormat("MMM", Locale.US);     
            Calendar mycal = Calendar.getInstance();
            mycal.set(Calendar.YEAR, 2017);
            mycal.set(Calendar.MONTH, month);
            int numDays = mycal.getActualMaximum(Calendar.DATE);
            System.out.println(" The no of days in the month of is "+ " "+ numDays);
        } 

    }
}