Bug in ArrayList iterator

[Remi Forax]

On 01/07/2015 11:47 AM, Daniel Fuchs wrote:
> On 07/01/15 11:31, Paul Sandoz wrote:
>>
>> On Jan 7, 2015, at 10:45 AM, Remi Forax <forax at univ-mlv.fr> 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);
>>>   }
>>>
>>> :(
>>>
>>
>> We could improve the best-effort basis by which 
>> ConcurrentModificationException is thrown by snapshotting the 
>> collection size on construction of the iterator (at the expense of an 
>> extra field, but that might pack into a spare 4 bytes due to 
>> alignment at least on 64 bits IIUC).

yes, note that AbstractList.Itr exhibit the same issue.
I fear that fixing this bug may break some programs.

>
> Or call checkForComodification() when cursor == size in hasNext()?

No, you can't.
The contract of AbstractList.modCount is pretty clear about that:
https://docs.oracle.com/javase/7/docs/api/java/util/AbstractList.html#modCount
hasNext() can not call checkForComodification().

>
> -- daniel

Rémi

>
>>
>> Paul.
>>
>>> Rémi
>>> tip: the bug lies in ArrayList.Itr.hasNext() (and 
>>> AbstractList.Itr.hasNext()).
>>>
>>
>