Basically, a private field or method can be accessed by any "instance of the class". This means that any method of any instance of that same class can access that private field or private method -- or the class itself (if the private field or method is static). We are talking about the same class.
In your example, you seem to imply that any class (even a different class type) can access any private field of an instance that it has an instance of. And no, that is not allowed in
Java -- for private, default, or protected fields or methods.
Henry