public class Nannichi {
public static void main(String[] args) {
if (args.length == 2) {
int year = Integer.parseInt(args[0]);
int month = Integer.parseInt(args[1]);
if (month >=1 && month <=12) {
System.out.println(new int[][]{{31,29,31,30,31,30,31,31,30,31,30,31},{31,28,31,30,31,30,31,31,30,31,30,31}}
[year % 4 == 0 && (year % 100 != 0 || year % 400 == 0) ? 0 : 1][month - 1]);
}
} else {
System.err.println("java Nannichi year month");
}
}
}
Calendarクラスを使うとどう変わりますか？