ConcurrentModificationException when using Iterator

Question

I'm trying to iterate an ArrayList with the Iterator. The problem is that I get the ConcurrentModificationException. I have checked a lot of questions like this. All said that the exception occurs when you modify an ArrayList while iterating through it. But I think that my problem is a little bit different because I'm not modifying the ArrayList even with the Iterator methods.

        Cliente cliente1 = new Cliente(16096,"Alberto1","pass",1500.0,false);

    ArrayList<Cliente> miLista = new ArrayList<Cliente>();

    Iterator<Cliente> miIterador = miLista.iterator();

    miLista.add(cliente1);

    System.out.println(miLista.get(0).nombre); //This displays "Alberto1"
    System.out.println(miIterador.hasNext()); //This displays 'true'
    miIterador.next(); //Here I get the exception

I don't know how to solve it. It could be a silly question because actually i'm beginner but I got stuck here.

Thank you.

--Well can't even answer my own question so I edit the question with the answer:

Thank you very much to all of you! You all give me the right answer :D Sorry for the silly question by the way :P

SOLVED

Reorder Iterator<Cliente> miIterador = miLista.iterator(); and miLista.add(cliente1); — toniedzwiedz
– toniedzwiedz, Commented Feb 23, 2014 at 13:41

Zeeshan · Accepted Answer · 2014-03-12 10:05:00Z

4

This line is the culprit. You can't modify a list after getting a iterator on it in any way except through the iterator's own remove or add methods.

miLista.add(cliente1);

The iterators returned by ArrayList class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException.

edited Mar 12, 2014 at 10:05

answered Feb 23, 2014 at 13:39

Zeeshan

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Comments

Zavior · Accepted Answer · 2014-02-23 13:39:20Z

3

" But I think that my problem is a little bit different because I'm not modifying the ArrayList even with the Iterator methods."

But you are modifying the list by adding an element :)

    ArrayList<Cliente> miLista = new ArrayList<Cliente>();

    Iterator<Cliente> miIterador = miLista.iterator();

    miLista.add(cliente1); 
    ^^^^^^^^^^^^^^^^^^^^^^ here!

answered Feb 23, 2014 at 13:39

Zavior

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RMachnik · Accepted Answer · 2014-02-23 13:41:29Z

1

This is the problematic line, you are morfing arraylist by adding object to it. Iterator is made on real array list so it throw exception as fail-fast style.

miLista.add(cliente1);

This is piece of code from arrayList class it is fired when you invoke getNext on iterator.

 final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }

answered Feb 23, 2014 at 13:41

RMachnik

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Warlord · Accepted Answer · 2014-02-23 13:42:12Z

0

You are modifying list after you produce the Iterator. Just swap lines

Iterator<Cliente> miIterador = miLista.iterator();

miLista.add(cliente1);

and everything will work fine.

answered Feb 23, 2014 at 13:42

Warlord

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Leo · Accepted Answer · 2014-02-23 13:53:18Z

0

One alternative is to use a ListIterator instead and rewind the iterator after you insert the new Client

    Cliente cliente1 = new Cliente(16096,"Alberto1","pass",1500.0,false);

    ArrayList<Cliente> miLista = new ArrayList<Cliente>();

    ListIterator<Cliente> miIterador = miLista.listIterator();

    miIterador.add(cliente1);
    miIterador.previous();

    System.out.println(miLista.get(0).getHombre()); //This displays "Alberto1" << notice you're not using the iterator here
    System.out.println(miIterador.hasNext()); //This displays 'true'
    System.out.println(miIterador.next().getHombre()); //This displays "Albert1" again

answered Feb 23, 2014 at 13:53

Leo

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