import javax.swing.JOptionPane;

//  File:  Irregular2D.java

//  Since a 2D array is just a 1D array of 1D arrays, each "row" can have a
//  different number of "columns."  That is, the elements of a 1D array can
//  point to 1D arrays of different sizes.
//  This class implements a 2D array of 13 rows (row 0 will not be used) - one
//  for each month.  The number of columns in each row is the number of days
//  in that month, plus one (column 0 will not be used).  So array of [10][15]
//  represents October 15th.
public class Irregular2D
{
    public static final String[] MONTH_NAMES =
    {
        "", "January", "February", "March",
        "April", "May", "June", "July",
        "August", "September", "October",
        "November", "December"
    };
    // MONTH_NAMES[0] has null string

    public static void main(String[] args)
    {
        String yearString = JOptionPane.showInputDialog("What Year?") ;
        int year = Integer.parseInt(yearString) ;
        boolean isLeapYear = (year % 4 == 0 && year % 100 != 0) 
                                            || 
                             (year % 400) == 0 ;
       
        String[][] calendar = new String[13][];
        // this is a 13 element array of pointers to String array.  Each 
        // pointer is currently null (see picture on board)

        // for each row (except the 0th) ...
        for (int month = 1; month <= 12; month++)
        {
            // 30 days hath September, April, June, and November...
            if (month == 9 || month == 4 || month == 6 || month == 11)
            {
                calendar[month] = new String[31] ;
            } 
            // if leap year February gets 30; otherwise 29
            else if (month == 2)
            {
                if (isLeapYear)
                {
                   calendar[month] = new String[30];   // 29 days
                }
                else
                {
                   calendar[month] = new String[29];   // 29 days
                }
            } 
            // other months have 31 days, so set to 32
            else
            {
                calendar[month] = new String[32];
            }
        }

        // print number of columns in each row (except the 0th)

        for (int month = 1; month < calendar.length; month++)
        {
            System.out.println(MONTH_NAMES[month] + " has "
                    + (calendar[month].length - 1) + " days.");
        }
    }
}

/* program output

January has 31 days.
February has 29 days.
March has 31 days.
April has 30 days.
May has 31 days.
June has 30 days.
July has 31 days.
August has 31 days.
September has 30 days.
October has 31 days.
November has 30 days.
December has 31 days.

*/