Inheritance of abstract methods with package access

Question

According section "8.1.1.1" of JLS we have:

A class C has abstract methods if either of the following is true:

• Any of the member methods (§8.2) of C - either declared or inherited - is abstract.

• Any of C's superclasses has an abstract method declared with package access, and there exists no method that overrides the abstract method from C or from a superclass of C

It is interesting, why do we have second option here. In particular, why do we have exactly "package access". And what about "public" or "protected" methods?

Answer 1

From order of most private to most open, the java modifiers go:

• private
• package
• protected
• public

Child classes cannot inherit the package methods of a parent class in another package. So a class inheriting from a such a parent would not be abstract according to rule 1. Therefore the 2nd rule exists to address the situation where a child class inherits from an abstract parent and is unable to provide an implementation of the abstract package methods.

It's a nonsensical situation, and I would never expect to see this in any program anywhere. But the language must be fully specified or you could end up with a weird bug that allows a class with undefined methods to be instantiated.