java - Why are interfaces static?

Question

Why can I not have a interface inside of a inner class? Why are they inherently static? Sorry if it's a stupid question, I've tried my best to google this again and again but I can't seem to wrap it around my head. As in why cannot I declare these in inner classes/local classes?

Also just as a confirmation, the reason we can have static final variables in a interface is because they do not specify the state or any of that sort of the implementation right? If we lose static and use just a final, we need a instance which makes no sense cause you can't instantiate a interface. Sorry, I really am confused, and I know I should just make another question but I think these two questions are somewhat related.

Answer 1

Think about what static means - "not related to a particular instance". So, as you point out, a static field of class Foo is a field that does not belong to any Foo instance, but rather belongs to the Foo class itself.

Now think about what an interface is - it's a contract, a list of methods that classes which implement it promise to provide. Another way of thinking about this is that an interface is a set of methods that is "not related to a particular class" - any class can implement it, as long as it provides those methods.

So, if an interface is not related to any particular class, clearly one could not be related to an instance of a class - right?

*Note, as @Owlstead points out, there are ways of defining interfaces within classes. But, for the purposes of wrapping your head around what an interface is (which seems to be what you're working on), I would ignore those possibilities for now as they distract from and possibly obscure the purpose of interfaces in general.