The Java® Language Specification, Java SE 7 Edition, Fourth Edition

9.2. Interface Members

The members of an interface are:

• Those members declared in the interface.

• Those members inherited from direct superinterfaces.

• If an interface has no direct superinterfaces, then the interface implicitly declares a public abstract member method m with signature s, return type r, and throws clause t corresponding to each public instance method m with signature s, return type r, and throws clause t declared in Object, unless a method with the same signature, same return type, and a compatible throws clause is explicitly declared by the interface.

It is a compile-time error if the interface explicitly declares such a method m in the case where m is declared to be final in Object.

It follows that is a compile-time error ...