如何在不使用任何库的情况下找到日期之间的星期天 [关闭]

Question

你好，我有一个作业，我不知道该怎么做

我必须找到从 1990 年到 2000 年之间的月份 firstday 的日期

Answer 1

class DayFinder {
public static void main(String[] args) {
    //Note that if you enter a date below year 1901 you will get error
    String entereddate1 = "01-01-1990";
    String entereddate2 = "01-01-2022";
    
    int date1 = Integer.parseInt(entereddate1.substring(0,2));
    int month1 = Integer.parseInt(entereddate1.substring(3,5));
    int year1 = Integer.parseInt(entereddate1.substring(6,10));

    int date2 = Integer.parseInt(entereddate2.substring(0,2));
    int month2 = Integer.parseInt(entereddate2.substring(3,5));
    int year2 = Integer.parseInt(entereddate2.substring(6,10));
    
    for(int year = year1; year <= year2; year++)
        for(int month = month1; month <= 12; month++)
            if(getDay(1,month,year).equals("Sunday"))
                System.out.println("01-"+month+"-"+year+" is Sunday");
}

private static String getDay(int date, int month, int year) {

    String[] days_name = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
    //Cumulative sum of days
    int[] month_days = {0,31,59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
    int days = (year - 1900-1) * 365 + month_days[month-1] + date + findLeapYears(year);

    return days_name[days%7];
}

//This find the number of leap of years from 1900 upto the year that is passed.
private static int findLeapYears(int year) {
    int leap_years = 0;
    for(int i = 1900; i <= year; i++) {
        if( ((i%4 == 0)  && (i%100 != 0)) || (i%400 == 0))
            leap_years += 1;
    }
    return leap_years;
}
}```