代码产生并发修改异常

Question

I've got the following code:

public static void pauseAllTimers() {
        for(Timer timer : Timer.allTimers) {
            timer.pause();

        }

    }

Where Timer instances are being added and removed to allTimers within one thread (as far as I can tell, unless I'm overseeing something in my code).

Why is my code yielding a Concurrent Modification Exception?

Answer 1

You're iterating over the collection while you're removing from it - assuming that pause() removes the timer. Don't do that - you're modifying a collection while you're still iterating over it, which is a concurrent modification even though there's only one thread.

Copy the set of timers to a list, and then iterate over that :

List<Timer> timers = new ArrayList<Timer>(Timer.allTimers);
for (Timer timer : timers) {
    timer.pause();
}