Java编写的日历，输入年月，输出这个月的日期与星期

import java.util.Scanner;

public class rili {

    public static void main(String[] args) {
        for (int g = 0; g < 100; g++) {
            Scanner in = new Scanner(System.in);
            System.out.println("\n请输入年份：");
            int year = in.nextInt();
            System.out.println("请输入月份：");
            int month = in.nextInt();
            int sum = 0;
            int k = 0;
            for (int i = 1; i <= month - 1; i++) {
                if (i == 2) {
                    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                        sum = sum + 29;
                    } else {
                        sum = sum + 28;
                    }
                } else {
                    if (i == 4 || i == 6 || i == 9 || i == 11) {
                        sum = sum + 30;
                    } else {
                        sum = sum + 31;
                    }
                }
            }
            for (int a = 1900; a <= year - 1; a++) {
                if (a % 4 == 0 && a % 100 != 0 || a % 400 == 0) {
                    sum = sum + 366;
                } else {
                    sum += 365;
                }
            }
            sum += 1;
            int wekday = sum % 7;
            System.out.println("日\t一\t二\t三\t四\t五\t六");
            for (int j = 1; j <= wekday; j++) {
                System.out.print("\t");
            }
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                if (month == 2) {
                    k = 29;
                } else if (month == 4 || month == 6 || month == 9 || month == 11) {
                    k = 30;
                } else {
                    k = 31;
                }
            } else {
                if (month == 2) {
                    k = 28;
                } else if (month == 4 || month == 6 || month == 9 || month == 11) {
                    k = 30;
                } else {
                    k = 31;
                }
            }
            for (int i = 1; i <= k; i++) {
                if (sum % 7 == 6) {
                    System.out.print(i + "\n");
                } else {
                    System.out.print(i + "\t");
                }
                sum++;
            }
        }
    }
}