Do Subclasses Inherit Private Instance Variables From Superclasses

Question

Do subclasses inherit private fields?

This question addresses the same problem but I don't quite understand how that satisfies the (seemingly) contradictory situations below.

http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html

Says that "A subclass does not inherit the private members of its parent class."

This means that it neither inherits private instance variables nor private methods right?

However, how does this work if it inherits a public accessor method from its parent? It returns an instance variable that it doesn't know exists?

Also, my computer science book (Baron's AP Computer Science A) has the correct answer to a question that says that "The (Subclass) inherits all the private instance variables and public accessor methods from the (Superclass)."

Isn't this in contraction to oracle's tutorial?

Thanks for your help

Answer 1

The accessor will work fine. Remember that the accessor runs in the "context" of the superclass and so the accessor will be able to see the member that's hidden from the subclasses.

As for the textbook, it depends on your point of view. The subclass inherits the private members in the sense that they are actually there inside instances of the subclass (so they'll take up memory, etc.), but the subclass will be unable to directly access them.

Answer 2

Think of it like an onion. Every level of hierarchy is a layer within the onion. For example, If class C extends Class B, which extends class A then an object of class C would look like:

Object of Class C

       -------------------------------------------------------------
       |                                                           | 
       |                   C and it's members                      |
       |                                                           |
       |    ------------------------------------------------       |
       |    |                                              |       |
       |    |              B and it's members              |       |
       |    |    ------------------------------------      |       |                                              
       |    |    |         A and it's members       |      |       |
       |    |    |                                  |      |       |
       |    |    ------------------------------------      |       |                                   
       |    ------------------------------------------------       |
       |                                                           |
       -------------------------------------------------------------            

So, an object of class C does have members of B and A. But it cannot access private members of B and A.

It can however access public and protected members of B and A.

So a public accessor function of B or A would allow this object of class C to access a private instance variable of the class B or class A "part" of the object.