Do subclasses inherit private fields?

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Most of the confusion in the question/answers here surrounds the definition of Inheritance.

Obviously, as @DigitalRoss explains an OBJECT of a subclass must contain its superclass’s private fields. As he states, having no access to a private member doesn’t mean its not there.

However. This is different than the notion of inheritance for a class. As is the case in the java world, where there is a question of semantics the arbiter is the Java Language Specification (currently 3rd edition).

As the JLS states (https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.2):

Members of a class that are declared
private are not inherited by
subclasses of that class. Only members
of a class that are declared protected
or public are inherited by subclasses
declared in a package other than the
one in which the class is declared.

This addresses the exact question posed by the interviewer: “do subCLASSES inherit private fields”. (emphasis added by me)

The answer is No. They do not. OBJECTS of subclasses contain private fields of their superclasses. The subclass itself has NO NOTION of private fields of its superclass.

Is it semantics of a pedantic nature? Yes. Is it a useful interview question? Probably not. But the JLS establishes the definition for the Java world, and it does so (in this case) unambiguously.

EDITED (removed a parallel quote from Bjarne Stroustrup which due to the differences between java and c++ probably only add to the confusion. I’ll let my answer rest on the JLS 🙂

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