Calendar.java

Below is the syntax highlighted version of Calendar.java from §2.1 Static Methods.

/*************************************************************************
 *  Compilation:  javac Calendar.java
 *  Execution:    java Calendar M Y
 *
 *  This program takes the month M and year Y and prints a
 *  calendar for that month.
 * 
 *  % java Calendar 7 2005
 *   July 2005
 *   S  M  T  W Th  F  S
 *                  1  2 
 *   3  4  5  6  7  8  9  
 *  10 11 12 13 14 15 16 
 *  17 18 19 20 21 22 23 
 *  24 25 26 27 28 29 30 
 *  31 
 *  
 *************************************************************************/

public class Calendar { 

   /**********************************************************************
    *  Given the month (M), day (D), and year (Y), return which day
    *  of the week it falls on according to the Gregorian calendar.
    *  For M use 1 for January, 2 for February, and so forth. Outputs
    *  0 for Sunday, 1 for Monday, and so forth.
    **********************************************************************/
    public static int day(int M, int D, int Y) {
        int y = Y - (14 - M) / 12;
        int x = y + y/4 - y/100 + y/400;
        int m = M + 12 * ((14 - M) / 12) - 2;
        int d = (D + x + (31*m)/12) % 7;
        return d;
    }

    // return true if the given year is a leap year
    public static boolean isLeapYear(int year) {
        if  ((year % 4 == 0) && (year % 100 != 0)) return true;
        if  (year % 400 == 0) return true;
        return false;
    }

    public static void main(String[] args) {
        int M = Integer.parseInt(args[0]);    // month (Jan = 1, Dec = 12)
        int Y = Integer.parseInt(args[1]);    // year

        // months[i] = name of month i
        String[] months = {
             "",                               // leave empty so that months[1] = "January"
             "January", "February", "March",
             "April", "May", "June",
             "July", "August", "September",
             "October", "November", "December"
        };

        // days[i] = number of days in month i
        int[] days = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

        // check for leap year
        if (M == 2 && isLeapYear(Y)) days[M] = 29;


        // print calendar header
        StdOut.println("   " + months[M] + " " + Y);
        StdOut.println(" S  M Tu  W Th  F  S");

        // starting day
        int d = day(M, 1, Y);

        // print the calendar
        for (int i = 0; i < d; i++)
            StdOut.print("   ");
        for (int i = 1; i <= days[M]; i++) {
            StdOut.printf("%2d ", i);
            if (((i + d) % 7 == 0) || (i == days[M])) StdOut.println();
        }

    }
}