DayWeek.java

/* 
1.2 Built-in types of Data
1.2.29 Day of theweek. 
Write a program that takes a date as input
and prints the day of the week that date
falls on.
Your program should take three command line
parameters: m(month), d (day), and y (year).
For m, use 1 for January, 2 for February,
and so forth. For output, print 0 for 
Sunday, 1 for Monday, 2 for Tuesday, 
and so forth. Use the following formulas, 
for the Gregorian calendar:
*/

public class DayWeek {
    public static void main(String[] args) {
        
        int m = Integer.parseInt(args[0]);
        int d = Integer.parseInt(args[1]);
        int y = Integer.parseInt(args[2]);

        int y0 = y - (14-m)/12;
        int x = y0 + y0/4 - y0/100 + y0/400;
        int m0 = m + 12 * ((14-m)/12) -2;
        int d0 = (d + x + (31*m0)/12)%7;

        System.out.println(d0);
    }
}