Re: what happen in for (x:List) and iterator when adding to List

Lew <>
Thu, 25 Sep 2008 09:30:07 -0400
George wrote:

I need to do a breadth-first search on a graph. So I need to have a
list for element and iterator over it while keep adding element in the
end of the list. I am currently using ArrayList in java 5. I
remembered vaguely something about the iterator is unpredictable when
the collection changed. Is it true?

Can I use
List<E> list=new ArrayList<E>;
for (ListIterator<E> it = list.listIterator(); it.hasNext(); )
{....; list.add(x);

Where does 'x' come from?

or can I use

 for (x:list){
.....; list.add(x);

Wouldn't that make the List grow until it hits OutOfMemoryError (OOME)?
(Isn't that the point of Andreas' response?)

Or is there a removal from the front of the List before the addition on the back?

Or do you intend to add something not already in the List?

As to your "vague" recollection about how Lists behave, OP, have you
considered reading the Javadocs?


The iterators returned by this 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.

Whether this holds varies from implementing class to implementing class.


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