输出一个年份和月份，打印该年该月的天数

public class Entrance {
    public static void main(String[] args) {
   String strYear=javax.swing.JOptionPane.showInputDialog("输入年份");
        int year =Integer.parseInt(strYear);
   String strMonth=javax.swing.JOptionPane.showInputDialog("输入月份");
        int month =Integer.parseInt(strMonth);
        switch(month){
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                System.out.println(year+"年"+month+"月有31天");
                break;
            case 2:
            if((year%4==0&&year%100!=0)||(year%400==0)){
                System.out.println(year+"年"+month+"月有29天");
            }
            else{
                System.out.println(year+"年"+month+"月有28天");
            }
            break;
            case 4:
            case 6:
            case 9:
            case 11:
                System.out.println(year+"年"+month+"月有30天");
        }
    }

}