Threading - Iterator.nextEntry(Unknown Source) - ValueIterator.next(Unknown

Question

Hi,
I have a swing application, in which I am using two threads. One thread, is the "main", and the other, takes care of every update to the UI. My program works fine for a few seconds, but then I get a weird error which breaks my UI update thread. The error itself is:
Exception in thread "Thread-2" java.util.ConcurrentModificationException
     at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
     at java.util.HashMap$ValueIterator.next(Unknown Source)
     at DrawFrame$allthread.run(DrawFrame.java:400)
     at java.lang.Thread.run(Unknown Source)
Which leads me to believe that the two threads are messing each other up. Lets take a look at some code.
This is the class which is created about 3 times a second, based upon when the user wants it to be.
class shooting { // this class is inside of the "allthread" class which implements Runnable
          private Point p;
          private Dimension size;
          private int deltaY;
          private int wtr;
          private boolean destroy = false;
          Rectangle recs = new Rectangle(); // This may have a factor
          private shooting(Point p, Dimension size, Color color, int deltaY) {
               this.wtr = 0 - size.height;
               this.p = p;
               this.size = size;
               this.deltaY = deltaY;
               recs.x = p.x;
               recs.y = p.y;
               recs.width = size.width;
               recs.height = size.height;
               rectangles.put(shotnumber, recs); // This may have a big factor as well (this goes into a hashmap)
               shotnumber++;
          public void paint(Graphics g) { // this part has a factor I believe
               if (g.getColor() != Color.red){
               g.setColor(Color.red);
               g.fillRect(recs.x, recs.y, recs.width, recs.height);
          So how I display this class on the UI, is like this:
          public void painters(Graphics g){
          for (allthread.shooting shot : shots) {
               shot.paint(g);
          }The painters method is called from my "public void paintComponent(Graphics g) {}", which I think updates when the computer thinks it needs to.
So I'm not exactly sure why its breaking, perhaps someone can tell from the error which I have listed at the top. I think one thread is trying to do something, which another thread is trying to do something at the same time to the same part of the code. That might not be it, but thats the best I have come up with in a week of confused droning about over this crazy madness.
Thanks for reading,
Nate
P.S. Thanks for the help, all questions will be answered in under 3 minutes - I'm right here watching this post until it is answered. Please ask any questions that you might have in order for me to provide you with information that I may have left out.

Answer 1

[Check this out.|http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collections.html#synchronizedMap(java.util.Map)]
I don't know if you'd consider throwing an exception as breaking... but check this out too.