从给定的月份/年份打印日历

Question

我正在做一个Java作业，它涉及在用户指定月份和年份后打印日历。我不能使用日历或日历类。我的问题是日历不能正确地打印月份的第一天是星期六。我已经看了我的代码大约一个小时了，我不确定哪里出了问题。我用Zeller的同余来计算月的第一天，它由“h”表示。

例如，2008年3月的日历（错误）如下所示：

     March 2008
Su Mo Tu We Th Fr Sa
 1 
 2  3  4  5  6  7  8 
 9 10 11 12 13 14 15 
16 17 18 19 20 21 22 
23 24 25 26 27 28 29 
30 31 

这是我的代码：

package calendar;

import java.util.Scanner;

public class Calendar
{
    private static int numDays = 0;
    private static int h = 0;
    public static boolean leap(int year)
    {
        if(((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    public static void firstDayOfYear(int year)
    {
        int month = 13;
        year--;
        h = (1 + (int)(((month + 1) * 26) / 10.0) + year + (int)(year / 4.0) + 6 * (int)(year / 100.0) + (int)(year / 400.0)) % 7;
        String dayName = "";
        switch(h)
        {
            case 0: dayName = "Saturday"; break;
            case 1: dayName = "Sunday"; break;
            case 2: dayName = "Monday"; break;
            case 3: dayName = "Tuesday"; break;
            case 4: dayName = "Wednesday"; break;
            case 5: dayName = "Thursday"; break;
            default: dayName = "Friday"; break;
        }
        System.out.println("The first day of the year is " + dayName);
    }
    public static void firstDayOfMonth(int month, int year)
    {
        if(month == 1 || month == 2)
        {
            month += 12;
            year--;
        }
        h = (1 + (int)(((month + 1) * 26) / 10.0) + year + (int)(year / 4.0) + 6 * (int)(year / 100.0) + (int)(year / 400.0)) % 7;
        String dayName = "";
        switch(h)
        {
            case 0: dayName = "Saturday"; break;
            case 1: dayName = "Sunday"; break;
            case 2: dayName = "Monday"; break;
            case 3: dayName = "Tuesday"; break;
            case 4: dayName = "Wednesday"; break;
            case 5: dayName = "Thursday"; break;
            default: dayName = "Friday"; break;
        }
        System.out.println("The first day of the month is " + dayName);
    }
    public static void numDaysInMonth(int month, int year)
    {
        int[] days = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

        if (month == 2 && leap(year)) days[month] = 29;
        numDays = days[month];
        System.out.println("The number of days in the month is " + numDays);
    }
    public static void printCal(int month, int year)
    {
        String[] monthNames = {"","January","February","March","April","May","June","July","August","September","October","November","December"};

        System.out.println("    " + monthNames[month] + " " + year);
        System.out.println("Su Mo Tu We Th Fr Sa");
        for (int i = 0; i < h - 1; i++)
            System.out.print("   ");
        for (int i = 1; i <= numDays; i++)
        {
            System.out.printf("%2d ", i);
            if (((i + h - 1) % 7 == 0) || (i == numDays)) System.out.println();
        }
    }
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter month (1-12): ");
        int month = input.nextInt();
        if(month < 1 || month > 12)
        {
            System.out.println("Invalid month. Valids inputs are 1-12.");
            System.exit(0);
        }
        System.out.print("Enter year: ");
        int year = input.nextInt();
        if(year < 1753)
        {
            System.out.println("Invalid year. Valid inputs are 1753 and beyond.");
            System.exit(0);
        }
        if(leap(year))
        {
            System.out.println(year + " is a leap year.");
        }
        else
        {
            System.out.println(year + " is NOT a leap year.");
        }
        firstDayOfYear(year);
        firstDayOfMonth(month, year);
        numDaysInMonth(month, year);
        printCal(month, year);
    }    
}

Answer 1

我知道你知道答案。但这里有一个快速修复（抱歉有点黑客），你可以合并它来修正周六的索引，而无需对代码做很多更改。

System.out.println("Su Mo Tu We Th Fr Sa");
        int xx = h == 0 ? 7 : h; // Correct the index for Saturday.
        for (int i = xx; i > 1; i--) // Reversing the loop condition
            System.out.print("   ");
        for (int i = 1; i <= numDays; i++) {
            System.out.printf("%2d ", i);
            if (((i + h - 1) % 7 == 0) || (i == numDays))
                System.out.println();
        }

Answer 2

问题是你的指数搞砸了。这意味着你从1而不是0开始你的月份和日子都很虚弱。然而在这里

h = (1 + (int)(((month + 1) * 26) / 10.0) + year + (int)(year / 4.0) + 6 * (int)(year / 100.0) + (int)(year / 400.0)) % 7

最后的%7使它从0开始！这会导致循环

for (int i = 0; i < h - 1; i++)
  System.out.print("   ");

成为

for (int i = 0; i < -1; i++)
  System.out.print("   ");

因为周六h是0。

要解决此问题，应以0开始函数中的所有索引。然后，当用户输入索引为1时，只需减去1并将其传递到函数中。这样，你就不会在所有数组前面出现空白条目（顺便说一句，它应该是位于类顶部的静态期末考试）。

Answer 3

从周六开始的每个月，你的代码都会有相同的问题。这意味着问题可能在这方面-

for (int i = 0; i < h - 1; i++)
  System.out.print("   ");

在这里将h设置为7而不是0将为您修复它。您可以在这里修复它，或者您可能需要从1到7而不是0到6开始h并当然进行其他必需的更改。