ClassCastException on collection generics for jdk8 working code

[Ali Ebrahimi]

I think root cause is same for both sample code: I think one question
should clear problem and that is how type inference work here:

List<Date> list = new ArrayList<>();
list.add(new Date());

List<Foo> cList = (List<Foo>) (List<?>) list;
Date date = (Date) cList.get(0);

What is result of type inference for "cList.get(0)" ?


Consider that:

Date date = (Date) ((Foo)cList.get(0));

have same result.

I think this is expected behavior.



On Sun, Jan 18, 2015 at 1:14 AM, Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> Hi,
> I think 8043741 got integrated in b46, so  I would rule that one out (also
> judging from the fix [1], which seems very localized to the synthetic
> nullcheck operators). We'll need to dig a bit deeper on this one - the
> behavior seems a bit weird, and I'm not sure this is intentional.
>
> I'll keep you posted - I agree with Remi that compiler-dev is the right
> mailing list for this one.
>
> Thanks
> Maurizio
>
>
> On 17/01/15 20:22, Remi Forax wrote:
>
>> I think this is due to the fix of 8043741 [1].
>> In my opinion, these legacy tests are buggy and because of a bug in the
>> compiler
>> it was working, and not the other way around.
>>
>> Anyway, it's just my opinion, there is a lot of corner cases around the
>> cast to an interface,
>> asking the experts is a better idea so I've CC compiler-dev.
>>
>> Rémi
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8043741
>>
>> On 01/17/2015 07:51 PM, Emanuel wrote:
>>
>>> Thank you Martijn, i didn't know :)
>>>
>>> here we go :
>>> https://gist.github.com/tglman/02eb98fb1c80386fa3ab
>>> https://gist.github.com/tglman/44b0b3fc4239d9229027
>>>
>>> Let me add also that OrientDB don't rely in any way on this behavior, it
>>> come out just from two not well written legacy test case ;).
>>>
>>> On 01/17/2015 05:11 PM, Martijn Verburg wrote:
>>>
>>>> Hi Emanuel,
>>>>
>>>> Good to see you today! OpenJDK mailing lists strip attachments so
>>>> you'll need to give a pastebin link or similar.
>>>>
>>>> Cheers,
>>>> Martijn
>>>>
>>>> On 17 January 2015 at 16:58, Emanuel <emanuele.tagliaferri at gmail.com
>>>> <mailto:emanuele.tagliaferri at gmail.com>> wrote:
>>>>
>>>>      I am at the Adopt OpenJdk hack day organized by the LJC, I am
>>>> running
>>>>      tests cases of OrientDB (open source java based NoSql) on JDK9
>>>> (Build
>>>>      b45 ), and i got some issue with the use of generics.
>>>>
>>>>      basically this code:
>>>>              List<Date> list = new ArrayList<>();
>>>>              list.add(new Date());
>>>>
>>>>              List<Foo> cList = (List<Foo>) (List<?>) list;
>>>>              Date date = (Date) cList.get(0);                        //
>>>> it
>>>>      fail here
>>>>
>>>>      on jdk8 it work fine, on jdk9 the code fail in the marked line.
>>>>
>>>>      the jdk8 bytecode for the failing line is:
>>>>            invokeinterface #7,  2            // InterfaceMethod
>>>>      java/util/List.get:(I)Ljava/lang/Object;
>>>>            checkcast     #4                  // class java/util/Date
>>>>
>>>>      instead of  on jdk9 is:
>>>>            invokeinterface #7,  2            // InterfaceMethod
>>>>      java/util/List.get:(I)Ljava/lang/Object;
>>>>            checkcast     #8                  // class ListFail$Foo
>>>>            checkcast     #4                  // class java/util/Date
>>>>
>>>>
>>>>      and is clear that there's a additional cast that is causing the
>>>>      exception.
>>>>
>>>>      I understand that this code is not the exactly clean and correct
>>>>      conceptually, but it may be a lot of this staff out there that can
>>>> be
>>>>      break by jdk9.
>>>>
>>>>      In attachment a couple of simple example for reproduce this issue.
>>>>
>>>>
>>>>      Regards
>>>>
>>>>      Emanuel
>>>>
>>>>
>>>>
>>>>
>>
>


-- 

Best Regards,
Ali Ebrahimi