Java: Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException

Question

i am currently trying to code my own little 2D Game. It's a Helicopter dodging rockets. these rockets flighing from right to the left. If they are outside of the Panel they should be deleted.

this is how it looks like:

private void doLogic() {


     Vector<Sprite> trash = new Vector<Sprite>();

     for (Movable mov : actors) {
        mov.doLogic(delta);
        Sprite check = (Sprite) mov;
        if (check.remove) {
            trash.add(check);
        }
    }

     if (trash.size() > 0) {
         for (Sprite s : trash) {
             actors.remove(s);
        }
    }

    for (int i = 0; i < actors.size(); i++) {
        for (int n = i + 1; n < actors.size(); n++) {

            Sprite s1 = actors.elementAt(i);
            Sprite s2 = actors.elementAt(n);

            s1.collidedWith(s2);
        }
    }

}

and my print:

    public void paintComponent(Graphics g) {
    super.paintComponent(g);

    if (!isStarted()) {
        return;
    }

    if (actors != null) {
        for (Drawable draw : actors) {
            draw.drawObjects(g);
        }
    }
}

that's the Error I get everytime a rocket leaves the Panelarea:

Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
    at java.util.Vector$Itr``.checkForComodification(Vector.java:1156)
    at java.util.Vector$Itr.next(Vector.java:1133)
    at GamePanel.paintComponent(GamePanel.java:339)
    at javax.swing.JComponent.paint(JComponent.java:1045)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210)
    at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5158)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4969)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

I hope you can help me :)

Answer 1

In the paintComponent() you can use Collections.public static <T> List<T> unmodifiableList(List<? extends T> list). Just pass the actors list and get a copy of the list.

Answer 2

You can't remove() from the collection while iterating it with the foreach-loop. You can do it by using a regular Iterator though, with the Iterator's remove() method.