Nested generics don't compile in 1.7.0_15, but do in 1.6.0_27.
Maurizio Cimadamore
maurizio.cimadamore at oracle.com
Mon Mar 11 10:25:06 PDT 2013
On 11/03/13 17:19, Dzmitry Lazerka wrote:
> I've found a workaround: to define
> abstract Class<? /*extends M*/> getModelClass();
> and implement it.
Yep - was just thinking about the same
> Although then we're not using compile-type checks, that were possible
> in openjdk 1.6.0.
Well, yes - but the fact that those checks were working was a bug. ;-)
As in my first email, it's possible that there's something that could be
loosened at the spec level - but for consistency sake it make sense for
now to treat your example as if it were
class HasId<I> {}
class Alert<T extends /*Some*/Object> extends _HasId<String>_ {}
class BaseController<M extends HasId<String>> {
// abstract Class<M> getModelClass();
}
Maurizio
>
> -----
> Best regards,
> Dzmitry Lazerka
>
>
> On Mon, Mar 11, 2013 at 10:08 AM, Dzmitry Lazerka <dlazerka at gmail.com
> <mailto:dlazerka at gmail.com>> wrote:
>
> Of course, but then how to return Class<Alert<?>>?
> AlertController.java:13: error: incompatible types
> return Alert.class;
> ^
> required: Class<Alert<?>>
> found: Class<Alert>
> 1 error
>
> And it's not possible to cast Class<Alert> to Class<Alert<?>>,
> types are incompatible.
>
> -----
> Best regards,
> Dzmitry Lazerka
>
>
> On Mon, Mar 11, 2013 at 10:05 AM, Maurizio Cimadamore
> <maurizio.cimadamore at oracle.com
> <mailto:maurizio.cimadamore at oracle.com>> wrote:
>
> On 11/03/13 17:02, Dzmitry Lazerka wrote:
>> By the way, override wouldn't work, and I don't see any
>> workaround:
>>
>> AlertController.java:11: error: AlertController is not
>> abstract and does not override abstract method
>> getModelClass() in BaseController
>> class AlertController extends BaseController<Alert<?>> {
>> ^
>> AlertController.java:12: error: getModelClass() in
>> AlertController cannot override getModelClass() in BaseController
>> Class<Alert> getModelClass() {
>> ^
>> return type Class<Alert> is not compatible with Class<Alert<?>>
>> where M is a type-variable:
>> M extends HasId<String> declared in class BaseController
>> 2 errors
>>
> The return type in AlertController should match the one in the
> superclass - if you had Class<M> in the super class and M is
> Alert<?> in the subclass, the return type should be
> Class<Alert<?>>.
>
> Maurizio
>
>>
>> -----
>> Best regards,
>> Dzmitry Lazerka
>>
>>
>> On Mon, Mar 11, 2013 at 3:41 AM, Maurizio Cimadamore
>> <maurizio.cimadamore at oracle.com
>> <mailto:maurizio.cimadamore at oracle.com>> wrote:
>>
>> Hi,
>> (cc'ing Alex)
>> if you do:
>>
>> class AlertController extends BaseController<Alert<Object>>
>>
>> or
>>
>> class AlertController extends BaseController<Alert<?>>
>>
>> The code and the override should compile.
>>
>> Said that, the behavior in JDK 7 is deliberate - the
>> supertypes of a raw type are all erased, which means the
>> supertype of Alert is just HasId and not HasId<String> as
>> you would expect. This is the result of this fix:
>>
>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6559182
>>
>> Alex, can you comment on this? JLS section on raw types
>> (4.8) only says that the supertypes of a raw type are the
>> erasure of such sypertypes - it doesn't say this should
>> be applied transitively. Also, Definition of type erasure
>> (4.6) doesn't say anything about supertypes.
>>
>> The rationale behind the fix for 6559182 is that all
>> supertypes of a raw type should be erased - which seems a
>> fair assumption when looking at the examples in 6559182 -
>> however, should those two cases be treated differently:
>>
>> Case A:
>>
>> class Foo<X> { }
>> class SubFoo<X> extends Foo<String> { }
>>
>> SubFoo sf = ...;
>>
>> Case B:
>>
>> class Foo<X> { }
>> class FooString extends Foo<String> { }
>> class SubFoo<X> extends FooString { }
>>
>> SubFoo sf = ...;
>>
>> In other words, is the fact that example (B) is using an
>> intermediate supertype that is not parameterized (but has
>> parameterized supertype) enough top warrant special
>> treatment?
>>
>>
>> Maurizio
>>
>>
>> On 11/03/13 03:25, Dzmitry Lazerka wrote:
>>> Hi,
>>>
>>> class HasId<I> {}
>>> class HasStringId extends HasId<String> {}
>>> class Alert<T extends /*Some*/Object> extends HasStringId {}
>>> class BaseController<M extends HasId<String>> {
>>> // abstract Class<M> getModelClass();
>>> }
>>> class AlertController extends BaseController<Alert> { //
>>> error here
>>> // @Override Class<Alert> getModelClass() {
>>> // return Alert.class;
>>> // }
>>> }
>>> compiles fine on OpenJDK6, but in OpenJDK7 gives:
>>>
>>> Controller.java:50: error: type argument Alert is not
>>> within bounds of
>>> type-variable T
>>> class Controller extends BaseController<Alert> {
>>> ^
>>> where T is a type-variable:
>>> T extends HasId<String> declared in class BaseController
>>>
>>> Note that there's rawtype warning at line 50, because
>>> Alert must be parameterized. If I do that, e.g. extends
>>> BaseController<Alert<Object>>, code compiles. But I
>>> cannot do that, because I need to implement getModelClass().
>>>
>>> Ubuntu 12.04.
>>>
>>> Is it a bug in 1.7.0_15? Can you suggest any workarounds?
>>>
>>> -----
>>> Best regards,
>>> Dzmitry Lazerka
>>
>>
>
>
>
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