Inner classes are allowed to be specified in 'uses' statement

[Peter Levart]

Hi Georgiy,

On 04/01/2016 04:52 PM, Georgiy Rakov wrote:
> Hello,
>
> currently inner classes are allowed to be specified in 'uses' 
> statement, for instance following code is compiled successfully by 
> JDKb111 javac:
>
>    a/module-info.java:
>    module a {
>         uses pkg.Outer.Inner;
>    }
>
>    a/pkg/Outer.java:
>    package pkg;
>    public class Outer{ public class Inner{} }
>
> Spec doesn't prevent it either. However in 1.1.3 
> <http://cr.openjdk.java.net/%7Emr/jigsaw/spec/lang-vm.html> it 
> prevents implementations specified in 'provides' statement to be inner 
> classes. According to my understanding inner class cannot be extended 
> by non-inner class, for instance "public class Impl extends 
> Outer.Inner { } " would cause:
>
>    error: an enclosing instance
>    that contains Outer.Inner is required
>    class Implem extends Outer.Inner {}
>    ^
>    1 error
>
> So could you please tell what is the purpose of allowing inner classes 
> to be specified in 'uses' statement, there seem to be no way to create 
> its implementation. Should it be prohibited by spec?
>
> The minimized testcase is attached; in order to run it please:
> 1. unzip attached archive on Windows machine;
> 2. rename test12\test_bat to test12\test.bat;
> 3. modify test.bat by changing JDK_HOME variable to point to your JDK 
> installation;
> 4. run test.bat.
>
> Thank you,
> Georgiy.

Not only in 'uses' statement. It would be impossible to specify them in 
'provides ... with ...' statement as implementation classes too as they 
by definition can't be instantiated without an outer instance (their 
constructors always contain an implicit parameter - the outer instance). 
What does compiler say for such case?

a/module-info.java:
module a {
     exports pkg;
     provides pkg.Service with pkg.impl.Outer.Inner;
}

a/pkg/Service.java:
package pkg;
public interface Service {}

a/pkg/impl/Outer.java:
package pkg.impl;
public class Outer { public class Inner implements pkg.Service { } }


Regards, Peter