DayOfTheWeek2

import java.util.Scanner;
import javax.swing.JOptionPane;
import java.lang.Math;
/*Write a program which takes a date in day/month/year format (e.g. 25/11/2015) and, if the date is valid,
 *then it presents the date in, for example, “Wednesday, 25th November 2015” format.
 *You must include the following functions:
 *numberEnding() which takes a day number returns “th”, “st”, “nd” or “rd”.
 *monthName() which takes a month number (1-12) and return “January”, or “February”, …
 *dayOfTheWeek() which takes a day, month and year and returns “Monday”, or “Tuesday”, …
 *The day of the week function should use the Gaussian algorithm…
 *w = (day + floor(2.6 * (((month + 9) % 12) + 1) - 0.2) + y + floor(y/4) + floor(c/4) - 2c) mod 7
 *where
 *Y: year-1 for January or February,
 *year for the rest of the year
 *y: last 2 digits of
 *c: first 2 digits of Y
 *w: day of week (0=Sunday,..6=Saturday)
 *mod 7 needs to return a positive number (even if the
 *passed value is negative.
 */

public class DayOfTheWeek {

        public static final int DAYS_IN_APRIL_JUNE_SEPT_NOV = 30;
        public static final int DAYS_IN_FEBRUARY_NORMALLY = 28;
        public static final int DAYS_IN_FEBRUARY_IN_LEAP_YEAR = 29;
        public static final int DAYS_IN_MOST_MONTHS = 31;
        public static final int NUMBER_OF_MONTHS = 12;

        public static void main(String[] args) {

                try
                {
                        String input = JOptionPane.showInputDialog("Enter date (day/month/year):");
                        Scanner scanner = new Scanner( input );
                        scanner.useDelimiter("/");
                        int day = scanner.nextInt();
                        int month = scanner.nextInt();
                        int year = scanner.nextInt();

                        if (validDate( day, month, year))
                        {
                                JOptionPane.showMessageDialog(null, (dayOfTheWeek(day, month, year)) + ", " + day + (numberEnding(day)) + " " + (monthName(month)) + " " + year);
                        }
                        else
                        {
                                JOptionPane.showMessageDialog(null, "" + day + "/" + month + "/" + year + " is not a valid date.",
                                                "Error", JOptionPane.ERROR_MESSAGE);
                        }
                        scanner.close();
                }
                catch (NullPointerException exception)
                {
                }
                catch (java.util.NoSuchElementException exception)
                {
                        JOptionPane.showMessageDialog(null, "No number entered.",
                                        "Error", JOptionPane.ERROR_MESSAGE);
                }

        }

        public static String numberEnding (int day)
        {
                String numberEnding = "";
                if (day >= 11 && day <= 13)
                {
                    numberEnding = "th";
                    return (numberEnding);
                }
               // int tenRemainder = day % 10;
                switch (day % 10)
                {
                case 1:
                    numberEnding = "st";
                    break;
                case 2:
                    numberEnding = "nd";
                    break;
                case 3:
                    numberEnding = "rd";
                    break;
                default:
                    numberEnding = "th";
                    break;
                }
                return (numberEnding);
        }

        public static String monthName (int month)
        {
            String monthName = "";
            switch(month)
            {
            case 1:
                monthName = "January";
                break;
            case 2 :
                monthName = "February";
                break;
            case 3 :
                monthName = "March";
                break;
            case 4 :
                monthName = "April";
                break;
            case 5 :
                monthName = "May";
                break;
            case 6 :
                monthName = "June";
                break;
            case 7 :
                monthName = "July";
                break;
            case 8 :
                monthName = "August";
                break;
            case 9 :
                monthName = "September";
                break;
            case 10 :
                monthName = "October";
                break;
            case 11 :
                monthName = "November";
                break;
            case 12 :
                monthName = "December";
                break;
            }
            return (monthName);
        }

        public static String dayOfTheWeek (int day, int month, int year)
        {
            /* y = (year-1) for January or February or (year) for every other month (last two digits of the year)
             * y = last two digits of the year
             * c = first 2 digits of year
             */
            int c = year / 100;
            int y = year % 100;
            if (month == 1 | month == 2)
            {
                y = y - 1;
            }
            int dayOfTheWeekValue = ((int)(day + Math.floor(2.6 * (((month + 9) % 12) + 1) - 0.2) + y + Math.floor(y/4) +
                    Math.floor(c/4) - 2*c) % 7);
            String dayOfTheWeek = "";
            switch(dayOfTheWeekValue)
            {
            case 1:
                dayOfTheWeek = "Monday";
                break;
            case 2:
                dayOfTheWeek = "Tuesday";
                break;
            case 3:
                dayOfTheWeek = "Wednesday";
                break;
            case 4:
                dayOfTheWeek = "Thursday";
                break;
            case 5:
                dayOfTheWeek = "Friday";
                break;
            case 6:
                dayOfTheWeek = "Saturday";
                break;
            default:
                dayOfTheWeek = "Sunday";
                break;
            }
            return (dayOfTheWeek);
        }

        public static boolean validDate( int day, int month, int year)
        {
                return ((year >= 0) && (month >= 1) && (month <= NUMBER_OF_MONTHS) &&
                                (day >= 1) && (day <= daysInMonth( month, year )));
        }

        public static int daysInMonth( int month, int year )
        {
                int daysInMonth = DAYS_IN_MOST_MONTHS;
                switch (month)
                {
                case 2:
                        daysInMonth = isLeapYear( year ) ? DAYS_IN_FEBRUARY_IN_LEAP_YEAR :
                                                                       DAYS_IN_FEBRUARY_NORMALLY;
                        break;
                case 4:
                case 6:
                case 9:
                case 11:
                        daysInMonth = DAYS_IN_APRIL_JUNE_SEPT_NOV;
                        break;
                default:
                        daysInMonth = DAYS_IN_MOST_MONTHS;
                        break;
                }
                return (daysInMonth);
        }

        public static boolean isLeapYear( int year )
        {
                return (((year%4 == 0) && (year%100 != 0)) || (year%400 == 0));
        }
}