Java garbage collection of circular references

gistfile1.java

/*
jball@localhost:~/tmp/javaref$ java -version
java version "1.6.0_30"
Java(TM) SE Runtime Environment (build 1.6.0_30-b12)
Java HotSpot(TM) 64-Bit Server VM (build 20.5-b03, mixed mode)
jball@localhost:~/tmp/javaref$ java JavaRef 
JavaRef$A@4fe5e2c3
JavaRef$Dog@7d8a992f
JavaRef$Tail@164f1d0d
JavaRef$A@8dc8569
JavaRef$Dog@64c3c749
JavaRef$Tail@7150bd4d
JavaRef$A@3ce53108
JavaRef$Dog@6af62373
JavaRef$Tail@459189e1
collecting tail
collecting tail
JavaRef$A@527c6768
collecting a
JavaRef$Dog@65690726
JavaRef$Tail@525483cd
collecting dog
shutting down
collecting dog
collecting a
collecting tail
collecting dog
collecting a
collecting tail
collecting dog
collecting a
*/

public class JavaRef {
  public static class A {
    public Dog dog;
    protected void finalize() {
      System.out.println("collecting a");
    }
  }

  public static class Dog {
    public Tail tail;
    protected void finalize() {
      System.out.println("collecting dog");
    }
  }

  public static class Tail {
    public Dog dog;
    protected void finalize() {
      System.out.println("collecting tail");
    }
  }

  public static void main(String[] args) {
    for (int i = 0; i < 4; i++) {
      createGarbage();
      System.gc();
    }

    System.out.println("shutting down");
  }

  private static void createGarbage() {
    A a = new A();
    Dog dog = new Dog();
    Tail tail = new Tail();
    a.dog = dog;
    dog.tail = tail;
    tail.dog = dog;

    System.out.println(a);
    System.out.println(dog);
    System.out.println(tail);
  }
}