Multiple this$1 fields when mixing subclassing and inner classes

[Stefan Reich]

Oh, I didn't know about those JDK 11 changes. That may in fact break the
idea of merging the references. I'm sure it can still be done, but might
require a spec change. And who's gonna pay for that?

:-D

Thanks

On Tue, 10 Sep 2019 at 01:17, David Holmes <david.holmes at oracle.com> wrote:

> On 10/09/2019 9:09 am, Stefan Reich wrote:
> >     But you're not talking about bytecode here you're talking about
> inside
> >     the VM. If there is an invokespecial on this$1 of type A then the
> >     constant pool lookup of its type will be A and we will resolve the
> call
> >     based on A's methods. If it were of type B then the resolution
> process
> >     would be different. There's nowhere to "insert a cast" here.
> >
> >
> > Can invokespecials on this$0/this$1 happen? I'm struggling to imagine a
> > case for this.
> >
> > invokespecial invokes private instance methods, superclass methods or
> > constructors. Superclass methods don't apply, neither do constructors.
> > And calls to private methods happen through bridges (just verified this
> > for myself again :):
> >
> >        13: aload_0
> >        14: getfield      #1                  // Field this$0:Lbla;
> >        17: invokestatic  #4                  // Method
> > bla.access$000:(Lbla;)V
> >
> > So what remains?
>
> This changed in JDK 11 with the addition of nestmates. Now inner classes
> have direct private access, no bridges needed, and we use invokespecial
> or invokevirtual as appropriate. For private methods invokevirtual is
> mainly used now, but of course we don't do virtual dispatch - there are
> special rules for private method resolution and selection.
>
> class A {
>    void m() {}
>    class InnerA {
>      void callM() { m(); }
>    }
> }
>
>   void callM();
>      descriptor: ()V
>      flags: (0x0000)
>      Code:
>        stack=1, locals=1, args_size=1
>           0: aload_0
>           1: getfield      #1                  // Field this$0:LA;
>           4: invokevirtual #13                 // Method A.m:()V
>           7: return
>        LineNumberTable:
>          line 4: 0
>
> >     BTW what introspection tool did you use to show this?
> >
> > My own tools ("JavaX")... here's the example program:
> > http://code.botcompany.de/1025166
>
> Thanks for the pointer.
>
> Cheers,
> David
>
> > Many greetings :)
>


-- 
Stefan Reich
BotCompany.de // Java-based operating systems