Accessing private instance variables of parent from child class?

Question

Let's say we have a class foo which has a private instance variable bar.

Now let us have another class, baz, which extends foo. Can non-static methods in baz access foo's variable bar if there is no accessor method defined in foo?

I'm working in Java, by the way.

Answer 1

No, not according to the java language specification, 3rd edition:

6.6.8 Example: private Fields, Methods, and Constructors

A private class member or constructor is accessible only within the body of the top level class (§7.6) that encloses the declaration of the member or constructor. It is not inherited by subclasses.

But regardless of this language restriction, you can access private fields through reflection:

Field privateStringField = 
   MyClass.class.getDeclaredField("privateString");
privateStringField.setAccessible(true);

String fieldValue = (String) privateStringField.get(privateObject);
System.out.println("fieldValue = " + fieldValue);

Answer 2

No, for that you should use protected.

Answer 3

For questions like this, where is a table found on the website here: http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html

Basically you want public or protected variable to be declared in foo since these are the variables that subclasses inherit from their parent and therefore seen in baz.

Answer 4

Child classes can not access private members (which is the whole point of private access control).

Answer 5

...if there is no accessor method defined in foo?

You need accessors. Besides, take care of inheritance, Should that var really be in parent? Remember IS-A check..

Answer 6

You cannot access private variables in descendent classes. Normally you'd want to use "protected" or "package" (the default) level access for this. However if you want to be really tricky, you can resort to using reflection and AccessibleObject to get at it. I wouldn't recommend doing that for production code unless you are really in a bind; for testing, etc., it's fine.

Answer 7

To use a private variable of a super class in a sub class, an accessor method is required. Else use the protected modifier instead of private.

Answer 8

The private variable(s) of a class invariably has a scope inside that class. If it has to be shared among the subclasses, it should be declared "protected"