输入某年某月某日，判断这一天是这一年的第几天？

import java.util.Scanner;

/**
 * @author 蓝色以太 从控制台输入月份，输出本月有多少天。
 */
public class Day {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int month, year;
        do {
            System.out.println("请正确输入年份：");
            year = sc.nextInt();
            System.out.println("请正确输入月份：");
            month = sc.nextInt();

        } while (month < 1 || month > 12 || year < 0);
        switch (month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12: {
            System.out.println(month+"月有31天！");
            break;
        }
        case 4:
        case 6:
        case 9:
        case 11: {
            System.out.println(month+"月有30天！");
            break;
        }
        case 2: {
            if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                System.out.println(month + "月有29天！");
            } else {
                System.out.println(month + "月有28天！");
            }
            break;
        }
        default: {
            System.out.println("error！");
            break;
        }
        }
    }
}