[statics] allowing static initializers in interfaces?

[John Rose]

In my latest (and probably 100th) lap around this
set of obstacles, I’ve used a workaround like the
following:

interface Something {
  default someMethod(int x) { return x * Private.SOME_CON; }
  /*should be private*/ static final class Private {
    private Private() { }
    private static final int SOME_CON = 42;
  }
}

The private class can contain private nested classes,
private static methods, and private constants, all
inaccessible outside of the interface nest.  A good use
of private nested classes would be classes which
provide one or more standard implementations
of the interface.

This pattern has the advantage of allowing a single-keyword
upgrade when private classes are eventually allowed, and also
a pretty small (though non-empty) API footprint today.

— John

> ----- Mail original -----
>> De: "John Rose" <john.r.rose at oracle.com>
>> À: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
>> Cc: "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
>> Envoyé: Mercredi 18 Novembre 2020 09:07:18
>> Objet: Re: [statics] allowing static initializers in interfaces?
> 
>> +1 from me too, and generally to heal the rift.
>> The inability to put private classes (and other “stuff”)
>> in an interface makes it hard to support canonical
>> algorithms in default methods, if they need auxiliary
>> types.
> 
> yes,
> another example, in the patch introducing the new random generator API currently under review, there is this method
> 
>  default float nextFloat() {
>    return (nextInt() >>> 8) * 0x1.0p-24f;
>  }
> 
> which a good example of why we also need private static final fields in interface.
> 
> Rémi
>