RFR: 8079136: Accessing a nested sublist leads to StackOverflowError (original) (raw)

Peter Levart peter.levart at gmail.com
Sat May 9 19:02:54 UTC 2015

Hi,

On 05/09/2015 04:36 PM, Ivan Gerasimov wrote:

On 09.05.2015 14:15, Doug Lea wrote: On 05/08/2015 02:17 PM, Ivan Gerasimov wrote:

The spec says "The returned list is backed by this list" and "The subclass's set(int, E), get(int), add(int, E), remove(int), addAll(int, Collection) and removeRange(int, int) methods all delegate to the corresponding methods on the backing abstract list".

It is possible that no differences could be detected, but it would take some effort to prove.

Hm. Let me try. We have two options: 1) Sublist of an arbitrary AbstractList, which is not SubList itself. 2) Sublist of another SubList. Plus: 3) An arbitrary wrapping of SubList, as seen for example in Collections utilities like synchronizedList: public List subList(int fromIndex, int toIndex) { synchronized (mutex) { return new SynchronizedList<>(list.subList(fromIndex, toIndex), mutex); } } ... which can define methods relying on the specified full cascade. Sorry, I cannot see how wrapping of SubList is different from any other dealing with the sublist's API. Shouldn't it remain as before, as long as we preserve the list's behavior?

I think Ivan is right here and this is safe, because SubList and RandomAccessSubList can not be overridden outside AbstractList. In a chain of sub-lists, there can be runs of consecutive [RandomAccess]SubList(s) intermingled with custom implementations that can not be SubList subclasses:

SubList at 1 -> SubList at 2 -> CustomSubListA -> CustomSubListB -> SubList at 3 -> SubList at 4 -> ListImpl

It is guaranteed that SubList.root pointers in above scenario will be (see SubList(AbstractList, ...) constructor):

SubList at 1.root == CustomSubListA SubList at 2.root == CustomSubListA SubList at 3.root == ListImpl SubList at 4.root == ListImpl

In order for a sub-list to be skipped with add,get,... invocations, it has to be a SubList (see SubList(SubList, ...) constructor). And there can be not custom SubList subclasses.

So no invocation of any custom method can be skipped.

Regards, Peter

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