同步后的Java并发修改异常

Question

I have a LinkedList of objects im trying to iterate over(using an iterator), see if they have any collision, if so, remove it from the list. However, I am getting a concurrent modification exception. I put it in a synchronized block, and I also tried catching the error in a try catch block, neither seem to help at all, the code is here:

private void updateTP() {
    synchronized (toiletpaper) {
        Iterator<ToiletPaper> iter = toiletpaper.iterator();
        while (iter.hasNext()) {
            ToiletPaper tp = iter.next();
            tp.update(1000, 700);
            if (toilet.overlaps(tp)) {
                System.out.println("tp splash!");
                toiletpaper.remove(tp);
                menu.removeLife();
            }
        }
    }
}

Any thoughts on the problem would be appreciated, I looked through here and google, and all of them said either catch the exception or synchronize it, which neither seem to work so... please help.

Answer 1

To avoid the exception, use iter.remove() instead. This will remove the element via the iterator instance, rather than the current call, which searches and removes from the list separately - that is, a concurrent modification.

Answer 2

It is throwing an exception because you're modifying the collection directly with toiletpaper.remove(tp); . You have to use iter.remove() to modify the collection while iterating over it.

Answer 3

When you do the toiletpaper.remove(tp) you modify your linked list (you relink it) and therefore you get that error; your iterator is no longer valid.