计算XX年的某月某日是当年的第多少天？是星期几？

/**
 * 编写程序，计算2013年的某月某日是当年的第多少天？是星期几？已知2013年元旦是星期二。
 */
import java.util.Scanner;
public class Date {
    public static void main(String[] args) {
        Scanner input=new Scanner(System.in);
        System.out.println("请输入年：");
        int year=input.nextInt();
        System.out.println("请输入月：");
         int month=input.nextInt();
         System.out.println("请输入日：");
        int day=input.nextInt();
        int days=0;
        int monthDay=0;
        int allDay=0;
        
           if (year <= 0 || month <= 0 || month > 12 || day <= 0 || day > 31) {
                  System.out.println("输入错误，请重新输入！");
                 
               }else{
                   if(month==1){
                       allDay=day;
                   } else{
           for (int i = 1; i < month; i ++) {
               switch (i) {
               case 1:
               case 3:
               case 5:
               case 7:
               case 8:
               case 10:
               case 12:
                  days = 31;
                  break;
               case 4:
               case 6:
               case 9:
               case 11:
                  days = 30;
                  break;
               case 2:
                  if ((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0))) {
                      days = 29;
                  } else{
                      days = 28;
                  }
                  break;
               }
               monthDay =monthDay+days;
           }
                   }
                   allDay=monthDay+day;
                   System.out.println(year +"年 "+month+"月"+day+"日是这一年的第" +allDay+"天。");
                   int x=(allDay+1)%7;
                   if(x==0){
                   System.out.println(year +"年" +month+ "月"+ day+ "日是这一年的星期天" );
                       }else {
                           System.out.println(year +"年" +month+ "月"+ day+ "日是这一年的星期"+x );
                        }
            }          
    }
}