Calendar object being buggy

Question

Hi, I'm not new to Java, but this seems like the best place for this question: I have some code dealing with parsing and reading schedules:
       Calendar now = Calendar.getInstance();
          Calendar startDateTime = (Calendar) startTime.clone();
          Calendar stopDateTime = (Calendar) stopTime.clone();
          startDateTime.set(Calendar.YEAR, now.get(Calendar.YEAR));
          startDateTime.set(Calendar.MONTH, now.get(Calendar.MONTH));
          startDateTime.set(Calendar.DATE, now.get(Calendar.DATE));
          stopDateTime.set(Calendar.YEAR, now.get(Calendar.YEAR));
          stopDateTime.set(Calendar.MONTH, now.get(Calendar.MONTH));
          stopDateTime.set(Calendar.DATE, now.get(Calendar.DATE));
          if (scheduleType == 0) //weekly
               for (int i = 0; i < schedule.length(); i = i + 3)
                    //System.out.println (TIMEFORMAT.format(startDateTime.getTime()));
                    startDateTime.set(Calendar.DAY_OF_WEEK, Integer.parseInt(schedule.substring(i, i + 1)));
                    stopDateTime.setTime(startDateTime.getTime());
                    stopDateTime.add(Calendar.DATE, Integer.parseInt(schedule.substring(i + 1, i + 3)));
                    System.out.println (TIMEFORMAT.format(startDateTime.getTime()) + " " + TIMEFORMAT.format(new Date()) + " " + TIMEFORMAT.format(stopDateTime.getTime()));
...My out put is:
2008-11-24 09:47:00.000 2008-11-10 10:26:14.981 2008-11-27 15:00:00.000
Which is not what I though I'd get (startDateTime and stopDateTime should be 2008-11-10, 2008-11-13).
However, if I uncomment the "System.out.println(TIMEFORMAT.format(startDateTime.getTime()));" right after the if statement, my out put becomes:
2008-11-10 09:47:00.000 2008-11-10 10:27:33.924 2008-11-13 15:00:00.000
Which is what I want.
This makes no sense to me, that System.out.println is apparently "changing" something. The closet I can figure is that System.out.println gives more time for something to do something. Shrugs.
I figure I can bandaid it by setting the startDateTime/stopDateTime to (Calendar) now.clone(), and then setting the specific hour, minute, second to the stopTime/startTime instead, but this is really bugging me.
Thanks for any help.

Answer 1

I've been working with java for 4-5 years, and I'm studying CS for my major, so I thought myself at least not new, but I suppose if the experienced say so, then I guess my self-estimation was wrong. Well, this is a good reality check.
Before anything else though, about what you said about .getTime() ("It is also setting startDateTime to the current time"). I'm under the impression that .getTime() get's the Calendar object's current time as a Date object (which as far as I've used, seems to be true) and also calculates the millisecond value. So if my Calendar is set to "January 2000", when I call .getTime() on it, do I get back a Date object set to "January 2000" (what I set it to) or "November 2008" (today's date)?
As for the program, I read in a schedule, a start_time, a stop_time (as well as the schedule_id, but that's not important) from a database, and create a schedule object. Then in one method of my Schedule object I check if the current time is in the schedule. I create startDateTime and stopDateTime objects on the fly since if the program runs overnight to the next week, a startDateTime, stopDateTime created at initialization will be wrong.
Here's a very heavily stripped down recreated version with a main and the test case I was using so you can run this.
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class Schedule2
     //date formatter
     private static final SimpleDateFormat TIMEFORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
     String schedule;
     Calendar startTime = Calendar.getInstance();
     public Schedule2(String schedule, Date startTime)
          this.schedule = schedule;
          this.startTime.setTime(startTime);
     public boolean nowInSchedule()
        Calendar now = Calendar.getInstance();
          Calendar startDateTime = (Calendar) startTime.clone(); //set the time values to correct values
          startDateTime.set(Calendar.YEAR, now.get(Calendar.YEAR)); //set the year/month/date values to correct ones
          startDateTime.set(Calendar.MONTH, now.get(Calendar.MONTH));
          startDateTime.set(Calendar.DATE, now.get(Calendar.DATE));
          for (int i = 0; i < schedule.length(); i = i + 3)
               //System.out.println(TIMEFORMAT.format(startDateTime.getTime()));
               startDateTime.set(Calendar.DAY_OF_WEEK, Integer.parseInt(schedule.substring(i, i + 1))); //sets current day_of_week to the one in the schedule
               System.out.println(TIMEFORMAT.format(startDateTime.getTime()));
               //when I check the startDateTime.getTime(), here is when I get the wrong date (2008-11-24 instead of the 10th)
          return false;
     public static void main(String [] args)
          Calendar a = Calendar.getInstance();
          a.set(1899, 12, 30, 10, 50, 0);
          Schedule2 sked = new Schedule2 ("203", a.getTime());
          System.out.println(sked.nowInSchedule());     
}So in my test case, I had "203" as the schedule, meaning every Monday until Thursday (first digit is Monday, second two is the number of days the schedule lasts) and the start_time as "30/12/1899 10:50:00 AM".
I expected to get back "2008-11-10" since this week's Monday falls on the second, but instead I got "2008-11-24".
I did read the Calendar API, but I suppose I didn't understand it fully. .set() updates the fields, but not the millisecond value. So, maybe .set(Calendar.DAY_OF_WEEK, ...) is not doing what I think it is doing because the millisecond value isn't computed yet, and .set(Calendar.DAY_OF_WEEK, ..) seems more complicated than just setting straight YEAR/MONTH/DATE.
I'm using Java 1.4.2 BTW.
Edited by: Yi.Liu on Nov 10, 2008 12:57 PM