Honestly, given that I literally write Java code for a living and think this case is mega confusing (granted, I've spent roughly 6 minutes reading about it), I am skeptical about the SC's ability to render a sensible verdict. But, meh, maybe it really can be abstracted out a legal principle.
How? The same exact way I own copyright to all of the code I write. It's the same exact system.
Yes, someone could copyright those if they weren't fundamental, obvious, and preexisting. The same way that if I write a novel new implementation of a String it is copyrighted under whatever license I choose. The same way that a new codec is copyrighted, etc.
It just seems a bit funny that the example you give to point out how obvious this standard must be is an implementation, not an interface. It would be weird to me that if I created a different String implementation with the same interfaces as your, that is prohibited.
I guess that with Java it's a little bit more straightforward, because the interface is a file that you must have created. But what if I create EvenBetterInterface and convince people to swap it out in their dependency injection and use my implementation, which otherwise has the same interfaces as yours? I feel that the interfaces they are talking about are supposed to be more that classical type of interface (a definition/promise with NO implementation details but assurance of functionality), and not the straight up Java (jesus christ, im sorry) "implementation" of an interface.