Nested generics don't compile in 1.7.0_15, but do in 1.6.0_27.

[Maurizio Cimadamore]

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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