What are the implicit specifier/modifiers of interface methods in Java 8?

Question

I understand that Interface methods are implicitly public. Java Docs Tutorial says

All abstract, default, and <

Answer 1

The language spec - specifically Section 9.4, states that abstract and public are implicit.

Every method declaration in the body of an interface is implicitly public (§6.6). It is permitted, but discouraged as a matter of style, to redundantly specify the public modifier for a method declaration in an interface.

An interface method lacking a default modifier or a static modifier is implicitly abstract, so its body is represented by a semicolon, not a block. It is permitted, but discouraged as a matter of style, to redundantly specify the abstract modifier for such a method declaration.

This is why IntelliJ warns you about it; by the JLS, you're doing something completely redundant.

As a bonus, fields in interfaces are implicitly public static final:

Every field declaration in the body of an interface is implicitly public, static, and final. It is permitted to redundantly specify any or all of these modifiers for such fields.