sealed interfaces vs. default methods

[Vicente Romero]

Hi Udo,

Thanks for your mail. I can't reproduce the bug in JDK16, we have been 
changing this area recently and the new code has been pushed to the 
JDK16 code base. Could you please double check if your code works in JDK16?

Thanks,
Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8258972

On 1/11/21 6:06 AM, Udo Höfel wrote:
> Dear all,
> I found some behavior of sealed generic interfaces with default methods that I find a bit unexpected. I put the examples from below also on GitHub ( https://github.com/uhoefel/java15_sealed_vs_default ).
> Example:
> Say we have an interface
>
> public sealed interface Interface<T> permits Impl_1 {}
>
> and, separately, the implementation
>
> public record Impl_1(Double value) implements Interface<Double> {}
>
> Running the following works just fine:
>
> public static void main(String[] args) {
>      Interface<Double> q = new Impl_1(3.0);
>      System.out.println(q instanceof Impl_1);
> }
>
> However, changing the interface to
>
> public sealed interface Interface<T> permits Impl_1 {
> 	default int foo() {
> 		return 1;
> 	}
> }
>
> That is, adding just a simple default method to the interface produces the following compile error:
>
> Exception in thread "main" java.lang.Error: Unresolved compilation problem:
> 	Permitted type Impl_1 does not declare eu.hoefel.java15_sealed_vs_default.using_both.Interface<T> as direct super interface
>
> 	at eu.hoefel.java15_sealed_vs_default.using_both.Interface.<clinit>(Interface.java:3)
> 	at eu.hoefel.java15_sealed_vs_default.using_both.Play.main(Play.java:5)
>
> Putting the record inside the interface and removing the permits clause makes it work again, though:
>
> public sealed interface Interface<T> {
>
> 	default int foo() {
> 		return 1;
> 	}
>
> 	public record Impl_1(Double value) implements Interface<Double> {}
> }
>
> I am on Windows 10 using
> openjdk version "15" 2020-09-15
> OpenJDK Runtime Environment (build 15+36-1562)
> OpenJDK 64-Bit Server VM (build 15+36-1562, mixed mode, sharing)
>   
> Also tested by a colleague with
> openjdk version "15.0.1" 2020-10-20
> OpenJDK Runtime Environment (build 15.0.1+9)
> OpenJDK 64-Bit Server VM (build 15.0.1+9, mixed mode)
>
> (Sorry if this doesn’t belong to this list)
>
> Best regards & stay healthy,
> Udo
>