ConcurrentModificationException in removing element in ArrayList [Using iterator.remove()]

Question

i know that we shouldn't modify the ArrayList during iteration.

But i'm using Iterator to iterate over list and iterator.remove() to remove the element but still results in ConcurrentModification Exception.

My program is not multithreaded.

I've many arraylist [class contains it and i'm processing many array of objects]

for(int i=0;i<obj.length;i++)
{
    if(k==i) continue;

    it = obj[i].arraylist.iterator();

    while(it.hasNext()){
    value = it.next();

      if(condn)  {
       it.remove();
       obj[k].arraylist.add(value);
       //k and i are not same 

      }

    }

}

Please provide complete code.

Ruchira Gayan Ranaweera
– Ruchira Gayan Ranaweera

2013-09-05 06:51:57 +00:00
Commented Sep 5, 2013 at 6:51 — Ruchira Gayan Ranaweera
– Ruchira Gayan Ranaweera, Commented Sep 5, 2013 at 6:51
Do you have a stacktrace? Looks ok to me.

Fildor
– Fildor

2013-09-05 06:52:47 +00:00
Commented Sep 5, 2013 at 6:52 — Fildor
– Fildor, Commented Sep 5, 2013 at 6:52

Amin Abu-Taleb · Accepted Answer · 2013-09-05 07:29:49Z

1

"Note that Iterator.remove is the only safe way to modify a collection during iteration; the behavior is unspecified if the underlying collection is modified in any other way while the iteration is in progress."

You can remove objects but not add new ones during the iteration, that's why you get that ConcurrentModificationException.

http://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html

Edit: You can also check:

if(k==i || obj[i].arraylist == obj[k].arraylist) continue;

edited Sep 5, 2013 at 7:29

answered Sep 5, 2013 at 6:51

Amin Abu-Taleb

4,5116 gold badges36 silver badges52 bronze badges

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

3 Comments

Fildor Over a year ago

Even if he is adding to another list? Mind "i" and "k" are made sure to be not the same. So I assume obj[i].arraylist and obj[k].arraylist are not the same instances, too.

Amin Abu-Taleb Over a year ago

@Fildor You are sure 'i' and 'k' are different, indeed, but you can't assume that the arraylists within obj[i] and obj[k] are not the same objects.

Fildor Over a year ago

If that is the case, then we have the flaw detected :) BTW: it should continue if the instances are the same, so, it should be obj[i].arraylist == obj[k].arraylist) , right?

WoooHaaaa · Accepted Answer · 2013-12-23 09:53:22Z

0

You can only modify the List during iteration using it variable.

answered Dec 23, 2013 at 9:53

WoooHaaaa

20.6k33 gold badges99 silver badges141 bronze badges

Collectives™ on Stack Overflow

ConcurrentModificationException in removing element in ArrayList [Using iterator.remove()]

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related