DayFinder.java

import java.util.*;     // for GregorianCalendar
import javax.swing.*;       // required for input dialogs

public class DayFinder {

    public static void main(String[] args) {

        /**
        *   Program :   DayFinder.java
        *   Purpose :   Displays the correct day of week for today's date,
        *            and for a date you select (in the past or future)
        *   Creator :   Chris Clarke
        *   Created :   06.01.2011
        */

        // create instance of calendar
        GregorianCalendar now = new GregorianCalendar();
        String message = "Today is ";
        int day = now.get(Calendar.DAY_OF_MONTH);
        int month = now.get(Calendar.MONTH);
        int year = now.get(Calendar.YEAR);
        int dayOfWeek = now.get(Calendar.DAY_OF_WEEK);
        displayWeekDay(message, day, month, year, dayOfWeek);
        String Day;
        Day = JOptionPane.showInputDialog("Enter a date: day of month (1-31)");
        String Month;
        Month = JOptionPane.showInputDialog("Enter a date: month (1-12)");
        String Year;
        Year = JOptionPane.showInputDialog("Enter a date: year (4 digits)");
        // convert Strings to integers
        try {
            day = Integer.parseInt(Day);
        }
        catch (Exception e) {
            System.out.print("Error in day input!");
            System.exit(0);
        }
        try {
            month = Integer.parseInt(Month);
        }
        catch (Exception e) {
            System.out.print("Error in month input!");
            System.exit(0);
        }

        month--;

        try {
            year = Integer.parseInt(Year);
        }
        catch (Exception e) {
            System.out.print("Error in year input!");
            System.exit(0);
        }
        // check that they're within acceptable range
        if (day<1 || day>31) {
            System.out.print("Error in day input! Number outside range");
            System.exit(0);
        }
        if (month<0 || month>11) {
            System.out.print("Error in month input! Number outside range");
            System.exit(0);
        }
        if (year<0 || year>3000) {
            System.out.print("Error in year input! Number outside range");
            System.exit(0);
        }
        GregorianCalendar d = new GregorianCalendar();
        d.set(year, month, day);
        message = "The day in question ";
        if (d.after(now))
            message += "will be a ";
        else
            message += "was a ";
        dayOfWeek = d.get(Calendar.DAY_OF_WEEK);
        displayWeekDay(message, day, month, year, dayOfWeek);
        // end of main program
    }//end main

    public static void displayWeekDay(String message, int day, int month, int year, int dayOfWeek) {
        String weekDay = "";
        switch (dayOfWeek) {
            case 1:     weekDay="Sunday"; break;
            case 2:     weekDay="Monday"; break;
            case 3:     weekDay="Tuesday"; break;
            case 4:     weekDay="Wednesday"; break;
            case 5:     weekDay="Thursday"; break;
            case 6:     weekDay="Friday"; break;
            case 7:     weekDay="Saturday"; break;
            default :   weekDay="Error";
        }
        // end of switch statement
        System.out.print(message+weekDay);
        System.out.println(" ("+day+"/"+(month+1)+"/"+year+")");
    }//end displayWeekDay
}//end class