java - Java 中的工作日查找器

Question

我正在做的项目包括:'编写一个程序，提示输入日期(月、日、年)并报告该日期是星期几。有可能知道 1601 年 1 月 1 日是星期一很有帮助。这是“Building Java Programs - A Back to Basics Approach, 2nd Edition”的练习，这本书是我买来自学 Java 的。非常感谢任何反馈，但我确实要求你解释为什么你会以另一种/某种方式做某事。谢谢!

所以，我的问题是，虽然对于接近 1600 年的日期，它给出了正确的日期(我相信)，但最近几天情况并非如此，它们有三天的偏移量(至少我的那些检查)。为什么会发生这种情况，我该如何解决？谢谢!

我的代码:

// finds the day of the week of the given date
public static String dayFinder(int month, int day, int year) {
    // handle invalid input
    if (month > 12 || month < 1 || day > 31 || day < 1) {
        throw new IllegalArgumentException("Month must be between "
                + "1 and 12 and Day must be between 1 and 31.");
    }

    // convert to "absolute" day, covering day and month
    int absoluteDay = monthToDay(month, day, year);

    // convert year to days and add to "absolute" day
    absoluteDay += yearToDay(year);

    if (absoluteDay % 7 == 1) {
        return "Monday";
    } else if (absoluteDay % 7 == 2) {
        return "Tuesday";
    } else if (absoluteDay % 7 == 3) {
        return "Wednesday";
    } else if (absoluteDay % 7 == 4) {
        return "Thursday";
    } else if (absoluteDay % 7 == 5) {
        return "Friday";
    } else if (absoluteDay % 7 == 6) {
        return "Saturday";
    } else { // absoluteDay % 7 == 0
        return "Sunday";
    }
}

// calculates the number of days present in a given
// date since the beginning of the year
public static int monthToDay(int month, int day, int year) {

    // convert to "absolute" day
    int absoluteDay = 0, daysTo31 = 0;

    // iterate through months
    for (int i = 0, loopMonth = month; i < month; i++) {
        if (loopMonth == 1 || loopMonth == 3 || loopMonth == 5 
                || loopMonth == 7 || loopMonth == 8 || loopMonth == 10
                || loopMonth == 12) {
            absoluteDay += 31;
            daysTo31 = 0;
        } else if (loopMonth == 2) {
            if (year % 4 != 0) {
                absoluteDay += 28;
                daysTo31 = 3;
            } else { // leap year
                absoluteDay += 29;
                daysTo31 = 2;
            }
        } else { // month = 4, 6, 9 or 10
            absoluteDay += 30;
            daysTo31 = 1;
        }
        loopMonth--;
    }

    // adjust to specific day
    absoluteDay -= (31 - day - daysTo31);       
    return absoluteDay;
}

// calculates the number of days between 
// (the beginning of) the given year and
// (the beginning of) the reference year 1601
public static int yearToDay(int year) {

    // convert to "absolute" day
    int absoluteDay = 0;
    year -= 1601; 

    // iterate through years
    for (int i = 0, loopYear = year; i < year; i++) {
        if (loopYear % 4 != 0) {
            absoluteDay += 365;
        } else { // leap year
            absoluteDay += 366;
        }
        loopYear--;
    }

    return absoluteDay;
} 

//1604 年 (MDCIV) 是星期四开始的闰年

Answer 1

您的问题可能与闰年有关。

由于维基百科:

除了能被 100 整除的年份外，所有能被 4 整除的年份都是闰年；能被 400 整除的世纪年仍然是闰年。例如，1900 年不是闰年； 2000 年是闰年。 [link]

这就是为什么你有太多三天(1700、1800、1900)的原因。