Bug in ArrayList iterator

David Holmes david.holmes at oracle.com
Thu Jan 8 02:24:54 UTC 2015

On 7/01/2015 7:45 PM, Remi Forax wrote:
> A simple Java question, what this code does ?
>    ArrayList<String> list = new ArrayList<>();
>    list.add("foo");
>    list.add("bar");
>    for(String s: list) {
>      list.remove(s);
>    }
> :(
> Rémi
> tip: the bug lies in ArrayList.Itr.hasNext() (and
> AbstractList.Itr.hasNext()).

This is not a bug. The only supported way to remove from a collection 
you are iterating over is to use an Iterator's remove method.


"The behavior of an iterator is unspecified if the underlying collection 
is modified while the iteration is in progress in any way other than by 
calling this method."

and as already pointed out the forEach docs make it clear you can't use 
forEach in such a context as the Iterator is not exposed to you.

So don't do that.


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