Re: Ada/JVM: cannot import abstract subprogram

[Shark8 <onewingedshark@gmail.com>]

On Saturday, March 23, 2013 8:53:07 AM UTC-6, John B. Matthews wrote:
> 
> In Java, it's possible to instantiate an anonymous subclass of an 
> abstract class [1], but it's a compile-time error to instantiate an 
> abstract class directly [2].
> 
> Absent first-hand experience with jvm2ada, might this represent a way 
> to enforce a similar compile-time restriction on an Ada client that 
> tries to import an abstract parent, rather than a concrete subclass?

No. It's the same sort of error to try to create an instantiation of an abstract type in Ada. -- The problem is that jvm2ada is "helpfully" transliterating the the class-structure for the Java API... but taking no account of whether or not a subprogram spec already translated is abstract or not, OR that the jvm-gnat compiler is unable to say "ah, 'abstract' is the same thing in Ada and in Java, so the 'import' should be of no effect."

I went with the heavy-handed/inelegant method of trying to compile [with the -k switch] and then commenting out the import pragmas which were flagged as errors. {A poor solution but one that allows me to generate a good* class-file.}

So now I'm stumped on some other errors, namely: "must override interface operation 'WindowOpened' at java-awt-event-windowlistener.ads:38" {and related}. This is kind of odd, because Ada 2005 got the Java-style interfaces ** and the reason for the [new] error seems to be interfaces: http://docs.adacore.com/gnatvm-docs/jgnat_ug.html#Using-Java-Interfaces

* Oddly the compilation neglects an 'adainit' function; in order to use Ada.Text_IO.Put/Put_Line I have to import it from a different class that was generated in attempting to get everything working.

** Er, so why does the jvm2ada program for GNAT 2012 not generate interface types?