What is the use of an empty abstract class?

Question

I want to know that is there any use of empty abstract class in Java? If so, what is it?

what-is-the-purpose-of-a-marker-interface: http://stackoverflow.com/questions/1023068/what-is-the-purpose-of-a-marker-interface — Thilo, Sep 28 '12 at 05:02
does "empty" also preclude having parent classes and interfaces? — Thilo, Sep 28 '12 at 05:03

score 7 · Accepted Answer · edited May 23 '17 at 12:28

7

An empty abstract class is very much equivalent to an interface except that it can extend a class

abstract class myAbstractClass // extends anotherClass implements anInterface
{

}

interface myInterface // extends anotherInterface
{

}

This pattern is called Marker interface and SO has a lot of good data about it already: What is the purpose of a marker interface?

edited May 23 '17 at 12:28

Community

answered Sep 28 '12 at 04:59

Azodious

or extend a class and "implement" one or more interfaces. Kind of like a junction type. – Thilo Sep 28 '12 at 05:01
yes, actually wanted to point out difference at compile time. – Azodious Sep 28 '12 at 05:06
In my book interfaces `extends` other interfaces. – maba Sep 28 '12 at 06:19

score 0 · Answer 2 · answered Sep 28 '12 at 05:00

0

you can only inherit from one abstract class. Then this is useful to avoid inheritance.

answered Sep 28 '12 at 05:00

Kalla

4

How is avoiding inheritance useful? – Thilo Sep 28 '12 at 05:01
1

what behaviour does an empty class have? – Thilo Sep 28 '12 at 05:05
What's 'final' about an abstract class? – user207421 Sep 28 '12 at 05:06
@EJP: an abstract class can have final methods (but an "empty" one cannot). – Thilo Sep 28 '12 at 05:07

score 0 · Answer 3 · answered Sep 28 '12 at 05:01

0

Yes, sometimes you need a base class for implement polymorphism.

answered Sep 28 '12 at 05:01

Rodrigo

Yes, sure, sorry. But the main difference is that you can implement some code in your base class, or define some attributes :) – Rodrigo Sep 28 '12 at 05:06

3 Answers3