Shared Calendar Object doesn't appear to be thread safe...

Hi there,

I've got what is probably an easy question for some of you.
I've got an application that downloads some data every hour at a certain time. I have a GUI that lists each item with a timer counting down until that task is run, at which point when it completes the timer resets.

The way I have it implemented is I use a single shared Class (Data) that is updated like so:

Timer timer = new Timer(true);
Calendar now = Calendar.getInstance();
timer.scheduleAtFixedRate(new TimerLoop(), 1000-now.get(Calendar.MILLISECOND), 1000);

private class TimerLoop extends TimerTask {
	public void run() {
		Data.now = Calendar.getInstance();
		Data.now.add(Calendar.MILLISECOND, -Data.now.get(Calendar.MILLISECOND));
		curTimeLabel.setText(sdf.format(Data.now.getTime()));
		Data.curMin = Data.now.get(Calendar.MINUTE);
		Data.curSec = Data.now.get(Calendar.SECOND);
	}
}

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Then, in each download thread, I have the following:

Timer timer = new Timer(true);
Calendar now = Calendar.getInstance();
timer.scheduleAtFixedRate(new DownloadLoop(), 1500-now.get(Calendar.MILLISECOND), 1000);

protected void updateLabels() {
	nextLabel.setText(timeLeftFormat.format(new Date(nextTry.getTimeInMillis() - Data.now.getTimeInMillis() + 5 * 60 * 60 * 1000)));
}

private class DownloadLoop extends TimerTask {
	public void run() {
		updateLabels();
	}
}

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whereby "nextLabel" is simply a JLabel to display the countdown and "nextTry" is the time at which the next download is to occur.

This works great with one download thread. The problem is that when I add more download threads, they occasionally show the same value, even if "nextTry" is different in each instance. I could understand this being a problem if any of the download threads tried to UPDATE Data.now, but as far as I know they should only be accessing it. I can't for the life of me figure out why the label would ever show the same number between two download threads if nextTry is different. Also, this doesn't happen every second, sometimes they show correctly, sometimes not (seemingly random).

Any thoughts? Better ways to achieve the same result?  I tried keeping a separate Calendar object in each download thread, but I found it resulted in the labels being updated at slightly different milliseconds which looked a little bit weird (the way I have it now has them all updating at the same time).

Thanks!