Static abstract method equivalent?

Question

From the forum thread:
http://forum.java.sun.com/thread.jspa?forumID=31&threadID=5202376
baftos wrote:
On the othe hand OP had a legitimate desire.
How can a superclass force its subclasses to
provide a certain class (as opposed to instance) behaviour?
Do other languages provide something like this?I like to have a static abstract method in a super abstract class:
public static abstract Behavior getClassMarker();And each sub concrete class should have:
public static Behavior getClassMarker(){
  return new Behavior(-- parameters --);
}Could we have an equivalent that current Java allows? Or, do we see some good news on the horizon?

Answer 1

Normally you create an instance with the metadata for the type, which annotations let you do:package dog;
abstract class Dog {
  abstract String getBark() ;
  Dog () {
    assert (getBreed() != null);
  DogBreed getBreed () { return getClass().getAnnotation(DogBreed.class); }
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface DogBreed {
  String genericBark () ;
  String name () ;
@DogBreed(name="Bulldog", genericBark="GrrrGrrrGrrr")
class Bulldog extends Dog {
  String getBark() {
    return "Grrr";
@DogBreed(name="Pomeranian", genericBark="Pirrr")
class Pomeranian extends Dog {
  String getBark() {
    return "Sausages";
public class DogAnnotationTest {
  public static void main (String...args) {
    Pomeranian pomme = new Pomeranian();
    System.out.println("The generic bark of the " + pomme.getBreed().name() + " breed is "
          + Pomeranian.class.getAnnotation(DogBreed.class).genericBark() + " but our  pomme cries "
          + pomme.getBark() + " for a jerky, his favorite food");
}The limitation is that you can only annotate with simple types, so you're stuck with the abstract factory pattern if you want the creation. Not that that's a bad thing, as it lets you create instances of classes which haven't been loaded yet.