Re: Collection implementations and fail-fast iterator problems.

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 02 Nov 2007 22:02:13 -0700

Message-ID:

<KdWdnXiZ86Z9nbHanZ2dnUVZ_uWlnZ2d@wavecable.com>

Roedy Green wrote:

On Fri, 02 Nov 2007 14:06:09 -0700, Daniel Pitts
<newsgroup.spamfilter@virtualinfinity.net> wrote, quoted or indirectly
quoted someone who said :

I'd like to avoid having to keep track of "to-be-deleted" and
"to-be-added" elements, but I don't see an elegant way to handle both
those cases without getting a ConcurrentModificationError.

see http://mindprod.com/jgloss/iterator.html#REMOVE

The problem is that the element to remove isn't necessarily the element
that the iterator is pointing to. For example.
class ItemHolder {
   Collection<Item> items;
   public void doAllSomething() {
    for (Item item: items) {
     item.doSomething();
    }
}

class Item {
   ItemHolder parent;
   public void doSomething() {
     for (Item item: parent.items) {
        item.affectBy(this);
        if (item.shouldBeRemovedNow()) {
           parent.items.remove(item);
        }
     }
     if (shouldAddNewItems()) {
        parent.items.add(createNewItem());
     }
   }
}

This is the gist of what happens. As you can see, there are multiple
iterators to deal with.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>