Odd ConcurrentModificationException

From:

Knute Johnson <september@knutejohnson.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 10 Dec 2013 09:41:27 -0800

Message-ID:

<l87jo5$5vt$1@dont-email.me>

I'm getting an odd ConcurrentModificationException in a MouseListener
when I try to remove an element from an ArrayList. The really strange
thing about it is that the exception occurs every other time I call
remove(). The ArrayList is only accessed on the EDT and I tried
wrapping it in Collections.synchronizedList but that made no difference.

The ArrayList variable is boxes and the type is DisplayBox, an extended
JComponent. The error shows the line number of the for instruction but
actually fails on the remove(box) call.

Any ideas on where to start looking?

Thanks,

knute...

     public void mousePressed(MouseEvent me) {
         if (me.getButton() == MouseEvent.BUTTON1) {
             System.out.println("Mouse1 Down");
             mouseDown = true;
             startX = me.getX();
             startY = me.getY();
         } else if (me.getButton() == MouseEvent.BUTTON3) {
             System.out.println("Mouse3 Down");
             for (DisplayBox box : boxes) {
                 if (box.getBounds().contains(me.getX(),me.getY())) {
                     remove(box);
                     boxes.remove(box);
                 }
             }
             repaint();
         }
     }

Mouse3 Down
Exception in thread "AWT-EventQueue-0"
java.util.ConcurrentModificationException

         at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
         at java.util.ArrayList$Itr.next(Unknown Source)
         at
com.knutejohnson.stationcasinos.backgroundgenerator.Yard$1.mousePress
ed(Yard.java:47)
         at java.awt.Component.processMouseEvent(Unknown Source)
         at javax.swing.JComponent.processMouseEvent(Unknown Source)
         at java.awt.Component.processEvent(Unknown Source)
         at java.awt.Container.processEvent(Unknown Source)
         at java.awt.Component.dispatchEventImpl(Unknown Source)
         at java.awt.Container.dispatchEventImpl(Unknown Source)
         at java.awt.Component.dispatchEvent(Unknown Source)
         at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown
Source)
         at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
         at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
         at java.awt.Container.dispatchEventImpl(Unknown Source)
         at java.awt.Window.dispatchEventImpl(Unknown Source)
         at java.awt.Component.dispatchEvent(Unknown Source)
         at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
         at java.awt.EventQueue.access$200(Unknown Source)
         at java.awt.EventQueue$3.run(Unknown Source)
         at java.awt.EventQueue$3.run(Unknown Source)
         at java.security.AccessController.doPrivileged(Native Method)
         at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
         at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
         at java.awt.EventQueue$4.run(Unknown Source)
         at java.awt.EventQueue$4.run(Unknown Source)
         at java.security.AccessController.doPrivileged(Native Method)
         at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
         at java.awt.EventQueue.dispatchEvent(Unknown Source)
         at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown
Source)
         at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
         at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown
Source)
         at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
         at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
         at java.awt.EventDispatchThread.run(Unknown Source)
--

Knute Johnson