Why can't my subclass access a protected variable of its superclass, when it's in a different package?

Question

I have an abstract class, relation in package database.relation and a subclass of it, Join, in package database.operations

Answer 1

A little known caveat about protected:

6.6.2 Details on protected Access

A protected member or constructor of an object may be accessed from outside the package in which it is declared only by code that is responsible for the implementation of that object.