CODEWITHSUNDEEP
javaandroid
karma
karma

Reputation: 1298

java.util.ConcurrentModificationException while using iterator

I have the following code to form a url, but some clients have reported exception at the for loop. java.util.ConcurrentModificationException at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:573)

    List<NameValuePair> requestParams = adRequest
            .createRequestParamsList(view.getContext());

    RequestTask currentTask = new RequestTask(this,
            view.getUserAgent(), view.getContext(), keyCode);

    try {
            currentTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                baseRequestUrl + Request.REQ_URI, requestParams);

    } catch (Exception e) {

    }

                String debugUrl = "";
                synchronized (this) {
                    debugUrl = baseRequestUrl + Request.REQ_URI + "?";
                    for (Iterator<NameValuePair> iterator = requestParams.iterator(); iterator.hasNext();) {
                        NameValuePair nvp = iterator.next();
                        debugUrl = debugUrl + nvp.getName() + "=" + nvp.getValue() + "&";
                    }
                    debugUrl = debugUrl.substring(0, debugUrl.length() - 1);
                }

requestParam is modified in RequestTask. why would it fail?

Upvotes: 0

Views: 313

Answers (2)

Fermin Silva
Fermin Silva

Reputation: 3377

After your comments, I suspect you should synchronize on the requestParams object, not on this.

The async task does not have a reference to the object that is iterating, so they are not locking on the same object, which is virtually the same as not synchronizing at all.

Make sure both classes synchronize on the same reference of the same object!

PS: if both classes do a synchronized(this), they are effectively synchronizing on different object instances.

Upvotes: 2

M. Shaw
M. Shaw

Reputation: 1742

When using an Iterator over an ordered set you must use iterator.remove() instead of <? extends Collection>.remove(). The latter yields a ConcurrentModificationException. If you are modifying requestParams in another thread and you must use the Iterator either have a field private Iterator iter in your class and provide a getIterator() method and perform the necessary null checks.

Upvotes: 0

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