ConcurrentModificationException when iterating on LinkedList

Question

I am not sure why this part of my code causes error but I know that if I remove an item from a list and I am just iterating through it at the same time I get this exception. I read that syncronizing would be another idea, but it is not always the right apporach. LogCat shows the ConcurrentModificationException for while (sw.hasNext()) row. Please note that other part of my code has abosultely no effect on the Lists.

Iterator<Weapons> sw = Selected_Weapons.iterator();
                while (sw.hasNext()) {
                    Weapons www = sw.next();
                        if (www.getY()<648){

                            Iterator<Container> cit2 = Containers.iterator();
                            while (cit2.hasNext()) {
                                Container c = cit2.next();

                                if (c.getWeaponID()==www.id){
                                    c.setWeaponID(-1);
                                    c.setIsEmpty(true);
                                    Selected_Weapons.remove(www);
                                }
                            }
                        }
                }

How can I solve this?

mjuarez · Accepted Answer · 2012-10-09 00:19:36Z

4

You're modifying the Selected_Weapons collection while it's being iterated. The offending line is actually:

Selected_Weapons.remove(www);

In this case, you might want to iterate over the collection, and just keep track of which ones you want to remove after you've iterated over all of the items.

answered Oct 9, 2012 at 0:19

mjuarez

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3 Comments

Steve Kuo Over a year ago

Or better yet, call Iterator.remove(). Then you don't need a separate collection.

Jani Bela Over a year ago

I dont know how to accept answer when you write it in a comment but I'd accept it at least 5 times. Great and tricky solution! Thanks!

Jani Bela Over a year ago

Because it went wrong 1 of 100 times today.. should I put sw.remove(); before the Selected_Weapons.remove(www) ?

Bobby Fisher · Accepted Answer · 2012-10-09 01:53:46Z

0

How about using ConcurrentLinkedList?

answered Oct 9, 2012 at 1:53

Bobby Fisher

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