Project Euler Problem 19

I've been solving these in order of ascending difficulty, but when sorting by problem number, I noticed that Problem 19 was the most difficult (according to the number of people who've solved it) within the first 20 problems. I was surprised because I thought this would be really easy, and it was. The code pasted below took me only 10 minutes to write, and was correct on the first try.

/*
 * Problem 19
 * 14 June 2002
 *
 * How many Sundays fell on the first of the month during the twentieth century
 * (1 Jan 1901 to 31 Dec 2000)?
 */

import org.joda.time.DateTime;

public class PE0019
{
 public static void main(String[] args)
 {
  int numberOfSundays = 0;
  int monthCounter = 0;
  
  DateTime startDate = new DateTime(1901, 1, 1, 0, 0, 0, 0);
  DateTime endDate = new DateTime(2000, 12, 31, 0, 0, 0, 0);
  
  DateTime currentDate = startDate;
  
  while (currentDate.getMillis() < endDate.getMillis())
  {
   currentDate = startDate.plusMonths(monthCounter++);
   if (currentDate.getDayOfWeek() == 7)
    numberOfSundays++;
  }
  
  System.out.println(numberOfSundays);
 }
}