10,000 calendar: enter a year, then enter another month, print out the calendar of that month that month
(January 1, 1900 is Monday).

import java.util.Scanner;

public class Main {
    
    public static void main(String[] args) {
    
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please enter the year:");
        int year = scanner.nextInt();
        System.out.println("Please enter the month:");
        int month = scanner.nextInt();
        int allDayOfYear = 0;// records between the days between 1900 and entering the year
        int allDayOfMonth = 0;// Number of days from January 1 to the input month
        int day = 0;// Record Entering the month of the month
        for(int i=1900;i<year;i++){
    
            if(i%4==0&&i%100!=0 || i%400==0){
    // true means that the year was a leap year
                allDayOfYear +=366;
            }else{
    
                allDayOfYear +=365;
            }
        }
        for (int i=1;i<month;i++) {
    
            switch (i) {
    
                case 1: case 3: case 5: case 7: case 8: case 10: case 12:
                    allDayOfMonth += 31;
                    break;
                case 4: case 6: case 9: case 11:
                    allDayOfMonth += 30;
                    break;
                case 2:
                    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
    
                        allDayOfMonth += 29;
                    } else {
    
                        allDayOfMonth += 28;
                    }
                    break;
            }
        }
        int allDay = allDayOfYear + allDayOfMonth + 1;//1900.1.1 to the total number of days on the first day of the input month
        int week = allDay % 7 ;// The first day of the month of the input month is the week of the week
        System.out.println("The first day of the month is week" 

 13 years -" + week);
        switch(month){
    
            case 1:case 3:case 5:case 7:case 8:case 10:case 12:
                day = 31;
                break;
            case 4:case 6:case 9:case 11:
                day = 30;
                break;
            case 2:
                if(year%4==0&&year%100!=0 || year%400==0){
    
                    day = 29;
                }else{
    
                    day = 28;
                }
                break;
        }
        System.out.println("----" + year + + month + "Month");
        System.out.println("One \ t two \ t three \ t four \ t five \ t six \ t days");
        int num = 0;// Control printing and replacement
        for (int i=1;i<week;i++){
    
            System.out.print("\t");
            num++;
        }
        for (int i=1;i<=day;i++){
    
            System.out.print(i + "\t");
            num++;
            if(num%7==0) {
    
                System.out.println();
            }
        }

    }
}