Adding new Attribute Interfaces to java-api.

[Tom Zeller]

>>I remember talking with Chad about the removal of interfaces, and I
>>think his line of reasoning was that what we lose in flexibility we
>>gain in simplicity, and the flexibility gained was 'never' used anyway
>>(my quotes).
>
> I don't think there's a meaningful gain in simplicity. It's one extra
> source file, and the Spring configuration is identical, as is the
> "receiving" end of the interface if it's injected as a dependency into
> something else.

I am having a hard time with this thread and the rename-Attribute
thread, I suggest that we talk on a dev call.

I remember talking to Chad about the interface removal, it was one of
the first things I asked him about, and I accepted his response as
satisfactory. But I just cannot reproduce here what he said, I do not
have good notes regarding that conversation.

I would need to take more time to look through the v2 and v3 IdP and
OpenSAML to see where Chad moved away from the
Interface+Abstract+Concrete model to just Concrete. If we decide that
we want to re-reverse that, then I think it will affect more than just
the 4 classes mentioned in the OP, and we would need to define some
sort of convention for which objects get an interface, because we
think those are plug-in points.