星期几，java 和 Zeller 的一致性！

Day of the week, java, and Zeller's congruence!

提问by aussie_aj

I'm doing this programming exercise out of a textbook where we are given an algorithm for calculating the day of the week called Zeller's congruence. Well do you think I can get the same output as the sample run in the textbook! They go with year 2002, month 3 and day of month 26. The sample reads back Tuesday. I've made several hours of mods and rewrites and can't get anywhere near Tuesday!

我正在根据教科书进行这个编程练习，其中给出了一种算法，用于计算一周中的某天，称为 Zeller 同余。好吧，您认为我可以获得与教科书中运行的示例相同的输出吗！它们与 2002 年、第 3 个月和第 26 个月的日期一致。样本读回星期二。我已经做了几个小时的修改和重写，但在星期二附近无法到达任何地方！

It's page 133 of Java Comprehensive textbook 8e if anyone has it... I'm a beginner so constructive feedback most welcome!

如果有人拥有它，它是 Java 综合教科书 8e 的第 133 页……我是初学者，因此非常欢迎有建设性的反馈！

Zeller's Congruence

泽勒的一致性

Your advice would be appreciated:

您的建议将不胜感激：

import java.util.Scanner;

public class DayOfTheWeek {

   public static void main(String[] args) {

   // Set up the scanner...
   Scanner input = new Scanner(System.in);

   // Set up the day's of the week with 0 being Sat as per algorithm.           
   final String[] DAY_OF_WEEK = {"Saturday", "Sunday", "Monday", 
       "Tuesday", "Wednesday", "Thursday", "Friday"};

   // Get the year       
   System.out.print("Enter the year (e.g., 2002): ");             
   int year = input.nextInt();

   // Get the month
   System.out.print("Enter the month 1-12: ");  
   int month = input.nextInt();

   // Get the day
   System.out.print("Enter the day 1-31: ");  
   int day = input.nextInt();

   // According to the algorithm Jan is 13 & Feb 14...
   if (month == 1) month = 13;
   else if (month == 2) month = 14;

   // j Is the century.
   int j = year / 100;

   // k Is the year of the century.
   int k = year % 100 ;

   // Calculate
   double h = (month + ((26*(month + 1)) / 10) + k + (k / 4) +
           (j / 4) + (5 * j)) % 7;

   // Cast answer back to integer to get result from array
   int ans = (int)h;

   // Print result
   System.out.println("Day of the week is: " + DAY_OF_WEEK[ans]);

   }
}

回答by Jon Lin

It looks like this line of code is wrong:

看起来这行代码是错误的：

double h = (month + ((26*(month + 1)) / 10) + k + (k / 4) +
(j / 4) + (5 * j)) % 7;

The formula has the dayadded to the first expression, not the month. So it should look like this:

该公式将日期添加到第一个表达式中，而不是月份。所以它应该是这样的：

double h = (day + ((26*(month + 1)) / 10) + k + (k / 4) +
(j / 4) + (5 * j)) % 7;

回答by Neil Armstrong

Zeller's Congruence requires INTEGER math in order to function properly. Here is the code in C/C++ (which was tested against the PHP day of week function for EVERY day from year 0 to year 10,000). All variables are of type int:

Zeller's Congruence 需要 INTEGER 数学才能正常运行。这是 C/C++ 中的代码（从第 0 年到第 10,000 年的每一天都针对 PHP 星期功能进行了测试）。所有变量都是 int 类型：

day_of_week = (((day + (((month + 1) * 26) / 10) + year + (year / 4) + (6 * (year / 100)) + (year / 400)) - 1) % 7);

Notice the "- 1" near the end of the function - this causes it to return a value from 0 thru 6 rather than 1 thru 7 to make the value easier to use, for example, as an index into a string array of day names.

请注意函数末尾附近的“- 1” - 这会导致它返回一个从 0 到 6 而不是 1 到 7 的值，以使该值更易于使用，例如，作为日期名称字符串数组的索引.

回答by amal

 double h = (month + ((26*(month + 1)) / 10) + k + (k / 4) +
       (j / 4) + (5 * j)) % 7;

is WRONG . Note that you dont use days in your current implementation.

是错的 。请注意，您在当前的实现中不使用天数。

回答by twister_void

This may work i don't have any idea about that book u may try this code

这可能有效我不知道那本书你可以试试这个代码

   import java.util.*;


public class Zeller {
    /**
     *
     * @param args (Not used)
     */
    final static String[] DAYS_OF_WEEK = {
            "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
            "Friday"
        };

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter the date in dd/mm/yyyy form: ");

        String[] atoms = input.nextLine().split("/");
        int q = Integer.parseInt(atoms[0]);
        int m = Integer.parseInt(atoms[1]);
        int y = Integer.parseInt(atoms[2]);

        if (m < 3) {
            m += 12;
            y -= 1;
        }

        int k = y % 100;
        int j = y / 100;

        int day = ((q + (((m + 1) * 26) / 10) + k + (k / 4) + (j / 4)) +
            (5 * j)) % 7;

        System.out.println("That date was a " + DAYS_OF_WEEK[day] + ".");
    }
}

回答by Sam

//just the modified version of the above code.

import java.util.*;

public class Zeller {

final static String[] DAYS_OF_WEEK = {
        "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
        "Friday"
    };

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter the date in dd/mm/yyyy form: ");

    String[] atoms = input.nextLine().split("/");
    int q = Integer.parseInt(atoms[0]);
    int m = Integer.parseInt(atoms[1]);
    int y = Integer.parseInt(atoms[2]);

    int dd,mm,yy;



    dd = q; mm =m; yy=y;

    if (m < 3) {
        m += 12;
        y -= 1;
    }

    int k = y % 100;
    int j = y / 100;

    int day = ((q + (((m + 1) * 26) / 10) + k + (k / 4) + (j / 4)) +
        (5 * j)) % 7;

    Calendar now = Calendar.getInstance();

    int nd,nm,ny;

    nm =  now.get(Calendar.MONTH) + 1;
    nd = (now.get(Calendar.DATE));
    ny = now.get(Calendar.YEAR);

    if(dd == nd && mm == nm && yy == ny)
        present(day);
    else if(yy<ny)
        past(day);
    else if(yy == ny)
            if(mm == nm)
                if(dd>nd)
                    future(day);
                else
                    past(day);
            else if(mm>nd)
                future(day);
            else 
                past(day);
    else 
        future(day);
}

public static void past(int day)
{
    System.out.println("That date was " + DAYS_OF_WEEK[day] + ".");
}

public static void future(int day)
{
    System.out.println("That date will be " + DAYS_OF_WEEK[day] + ".");
}

public static void present(int day)
{
    System.out.println("Toady is " + DAYS_OF_WEEK[day] + ".");
}
}

回答by omkarstha

import java.util.Scanner;

public class zelleralgorithm {

    public static void main (String[] args) {

        int month, dayOfMonth, year, cenNumber, yearNumber, weekday, counter = 0;
        String dayname = null;

        Scanner scan = new Scanner(System.in);

        System.out.println("\tZeller's Algorithm");
        System.out.println("**************************************");
        System.out.print("Enter month ( or 0 to exit):\t");
        month = scan.nextInt();


        //handling exception
        while(month > 12){
            System.out.println("Please enter a valid month!\n");
            System.out.print("Enter month ( or 0 to exit):\t");
            month = scan.nextInt();
        }


        while(month != 0) {
            System.out.print("Enter day:\t\t\t");
            dayOfMonth = scan.nextInt();


            //handling exception
            while(dayOfMonth > 32){
                System.out.println("Please enter a valid date!\n");
                System.out.print("Enter day:\t\t\t");
                dayOfMonth = scan.nextInt();
            }


            System.out.print("Enter year:\t\t\t");
            year = scan.nextInt();

            if(month == 1 || month == 2){
                month = 11;
                --year;
            }
            else{
                month = month -2;
            }

            cenNumber = year / 100;
            yearNumber = year % 100;

            weekday = (( (int) (2.6*month-.2) + dayOfMonth + yearNumber + (yearNumber/4) + (cenNumber/4) - (2*cenNumber)) % 7);

            if(weekday < 0){
                weekday = weekday + 7;
            }

            switch(weekday){
            case 0:
                dayname = "Sunday";
                break;
            case 1:
                dayname = "Monday";
                break;
            case 2:
                dayname = "Tuesday";
                break;
            case 3:
                dayname = "Wednesday";
                break;
            case 4:
                dayname = "Thursday";
                break;
            case 5:
                dayname = "Friday";
                break;
            case 6:
                dayname = "Saturday";
                break;
            default:
                dayname = "Exceptional Case error!!";
            }

            System.out.println("\n**************************************");
            System.out.println("\tThe day is "+ dayname);
            System.out.println("**************************************");

            System.out.print("\nEnter month ( or 0 to exit):\t");
            month = scan.nextInt();

            ++counter;
        }
        //while loop end

        //counter
        System.out.println("Number of entries = " + counter);

        scan.close();

    }
}