Tæl antal dage ud fra en speciel dato, skudår!

java har indbygget funktionalitet til at finde ugedag, men jeg antager at det skal
kodes selv

til inspiration fra lageret:

import java.util.*;

public class WeekDay {
  private static final String[] dayname = {
          "Sunday",
        "Monday",
        "Tuesday",
        "Wednesday",
        "Thursday",
        "Friday",
        "Saturday" };
  // The java way
  public static String wd1(int y, int m, int d) {
      Calendar c = new GregorianCalendar();
      c.set(Calendar.YEAR, y);
      c.set(Calendar.MONTH, m-1);
      c.set(Calendar.DAY_OF_MONTH, d);
      return dayname[c.get(Calendar.DAY_OF_WEEK) - 1];
  }
  // The elegant way
  public static String wd2(int y, int m, int d) {
      int a = (14 - m) / 12;
      int yx = y - a;
      int mx = m + 12*a - 2;
      int daynum = (d + yx + yx/4 - yx/100 + yx/400 +31*mx/12) % 7;
      return dayname[daynum];
  }
  // The straigth forward way
  private static boolean isLeapYear(int y) {
      return ((y % 4 == 0 && y % 100 != 0) || (y % 400 == 0));
  }
  private static final int[][] month = { {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
                                          {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335} };
  public static String wd3(int y, int m, int d) {
      int daynum = 0;
      daynum += ((y-1) * 365 + (y-1)/4 - (y-1)/100 + (y-1)/400); // years
      daynum += month[isLeapYear(y)?1:0][m-1]; // months
      daynum += (d - 1); // days
      daynum = (daynum + 1) % 7; // first day of week = monday
      return dayname[daynum];
  }
  private static void test(int y, int m, int d) {
      System.out.println(wd1(y, m, d) + " " + wd2(y, m, d) + " " + wd3(y, m, d));
  }
  public static void main(String[] args) {
      test(2003, 12, 4);
      test(2003, 12, 24);
      test(2004, 12, 8);
      test(2000, 12, 31);
      test(1900, 1, 1);
      for(int y = 1800; y <= 2100; y++) {
        for(int m = 1; m <= 12; m++ ) {
            for(int d = 1; d <= 28; d++) {
              if(wd1(y, m, d) != wd2(y, m, d)) {
                  System.out.println("problem wd2 : " + d + "-" + m + "-" + y);
              }
              if(wd1(y, m, d) != wd3(y, m, d)) {
                  System.out.println("problem wd3 : " + d + "-" + m + "-" + y);
              }
            }
        }
      }
  }
}

OK ?

Lækkeri!