Inheritance

[Mark Mahieu]

Hi Zdeněk,

I think the problem here is that the types { => Integer }, { =>  
Number } and { => Object } are all instances of the same generic  
interface (javax.lang.function.O<R,X>) but with different type  
arguments, and according to the JLS :


"A class may not at the same time be a subtype of two interface types  
which are different invocations of the same generic interface  
(§9.1.2), or an invocation of a generic interface and a raw type  
naming that same generic interface.

...

This requirement was introduced in order to support translation by  
type erasure (§4.6)."

(From http://java.sun.com/docs/books/jls/third_edition/html/ 
classes.html#8.1.5 )


Regards,

Mark


On 16 May 2008, at 08:32, tronicek at fel.cvut.cz wrote:

> Hi,
>
> this is compilable:
>
>     interface J1 {
>         Integer invoke();
>     }
>
>     interface J2 {
>         Number invoke();
>     }
>
>     interface J3 {
>         Object invoke();
>     }
>
>     interface J4 extends J1, J2, J3 { }
>
>     class C3 implements J1, J2, J3 {
>         public Integer invoke() { return null; }
>     }
>
>     class C4 implements J4 {
>         public Integer invoke() { return null; }
>     }
>
> and this is not:
>
>     interface I1 extends { => Integer } { }
>
>     interface I2 extends { => Number } { }
>
>     interface I3 extends { => Object } { }
>
>     interface I4 extends I1, I2, I3 { }
>
>     class C1 implements I1, I2, I3 {
>         public Integer invoke() { return null; }
>     }
>
>     class C2 implements I4 {
>         public Integer invoke() { return null; }
>     }
>
> But probably should be. As well as this:
>
>     interface Simple extends { => Integer }, { => Number }, { =>  
> Object } { }
>
> Zdenek
> -- 
> Zdenek Tronicek
> Department of Computer Science and Engineering
> Prague                   tel: +420 2 2435 7410
> http://cs.felk.cvut.cz/~tronicek
>
>
>
>
>
>

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