Problem with designing class

Question

I have a classes as below

public class Book extends Item{ ...}
public class DVD extends Item{ ...}

Book can be of type REFRENCE or ISSUE. DVD can be of type ISSUE only.

So should I create Item as follows?

public class Item {

  public enum ItemType{REFRENCE,ISSUE};
  ItemType itemtype;

}

Or I should declare seperate enum for both book and DVD?

Answer 1

It depends. Is a DVD ISSUE the same as a book ISSUE?

If so then put it in the parent class and throw an exception if you create a REFERENCE DVD.

If it isnt then define seperate public enums in the two subclasses.

Answer 2

How about defining two interfaces Reference and Issue and Book will implement both while DVD will implement only Issue?

Answer 3

By storing something's type in an enum you are going against using the object oriented features of the language. Also, I don't feel that an "item" "has a" property of being an issue/reference. It's more of an "is a" relation, which suggests you should use inheritence/interfaces. Of course the right approach depends on what your program is meant to do. Sometimes object oriented constructs can get in your way.