Java ConcurrentModificationException thrown when not modifying collection

Question

I'm doing a very simple "filter" on an ArrayList, which is occassionally throwing a ConcurrentModifificationException, but AFAICT there's no modification happening... The code is pretty straightforward...

public ArrayList<JSONObject> getContributionsByInstallation(int installationID, ArrayList<JSONObject> list){
    ArrayList<JSONObject> filtered = new ArrayList<JSONObject>();
    for(JSONObject object : list) {
        try {
            int fk = object.getInt("exhibit_fk");
            if(fk == installationID){
                filtered.add(object);
            }
        } catch(JSONException e){

        }
    }
    return filtered;
}

What am I missing?

/EDIT: adding stack trace

07-12 12:39:24.135: E/AndroidRuntime(2350): FATAL EXCEPTION: main
07-12 12:39:24.135: E/AndroidRuntime(2350): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.whatever.light/com.whatever.light.InstallationDetailActivity}: java.util.ConcurrentModificationException
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.os.Looper.loop(Looper.java:130)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread.main(ActivityThread.java:3691)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at java.lang.reflect.Method.invokeNative(Native Method)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at java.lang.reflect.Method.invoke(Method.java:507)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at dalvik.system.NativeStart.main(Native Method)
07-12 12:39:24.135: E/AndroidRuntime(2350): Caused by: java.util.ConcurrentModificationException
07-12 12:39:24.135: E/AndroidRuntime(2350):     at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:576)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.whatever.light.data.ContributionsData.getContrubtionsByInstallation(ContributionsData.java:81)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.whatever.light.data.ContributionsData.getRandomCommentContribution(ContributionsData.java:62)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.whatever.light.installations.ContributeCommentModuleFragment.showComment(ContributeCommentModuleFragment.java:102)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at com.whatever.light.installations.ContributeCommentModuleFragment.onCreateView(ContributeCommentModuleFragment.java:86)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:844)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1053)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1371)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:499)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.Activity.performStart(Activity.java:3817)
07-12 12:39:24.135: E/AndroidRuntime(2350):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1624)
07-12 12:39:24.135: E/AndroidRuntime(2350):     ... 11 more

seemingly the passed ArrayList<JSONObject> list is modified by another thread while iterating, you should make a copy of it using new ArrayList<JSONObject>(list); — s106mo
– s106mo, Commented Jul 12, 2012 at 17:50
@s106mo that makes sense and appears to work - if you post your comment as an answer I'll accept it — momo
– momo, Commented Jul 12, 2012 at 17:57

Sean Owen · Accepted Answer · 2012-07-13 17:40:03Z

1

Almost certainly, another thread is modifying the object referred to by list -- this method isn't. Look for all possible ways this could be happening.

answered Jul 13, 2012 at 17:40

Sean Owen

67k23 gold badges144 silver badges175 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

mkbsc · Accepted Answer · 2012-07-12 18:05:25Z

0

You can also use CopyOnWriteArrayList to avoid concurrentModificationException.. you can refer to this link which illustrates arrayList and CopyOnWriteArrayList..

http://techvivek.wordpress.com/2009/08/29/difference-between-arraylist-and-copyonwritearraylist/

answered Jul 12, 2012 at 18:05

mkbsc

1072 gold badges3 silver badges7 bronze badges

Collectives™ on Stack Overflow

Java ConcurrentModificationException thrown when not modifying collection

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related