Object reference casting code

[April.Johnson]

Take a look at this code:

interface Animal{}
interface Mammal extends Animal{}
class Horse implements Mammal{}
class Arabian extends Horse{}
class QH extends Horse{}
class Dog implements Mammal{}
class BorderCollie extends Dog{}
class GermanShepherd extends Dog{}
public class RefTest
{
public static void main(String args [])
{
1. Object o;
2. Animal a;
3. Mammal m;
4. Horse h = new Horse();
5. Arabian arabian = new Arabian();
6. QH qh = new QH();
7. Dog d = new Dog();
8. BorderCollie b = new BorderCollie();
9. GermanShepherd g = new GermanShepherd();
10. Animal [] aa = new Animal[6];
11.Mammal [] ma = new Mammal[6];
12. a = h;
13. a = arabian;
14. a = qh;
15. a = d;
16. a = b;
17. a = g;
18. h = (Horse)a;
19. h = a;
20. m = a;
21. m = (Mammal)a;
22. d = m;
23. d = (Dog)m;
24. System.out.println(d == g);
25. a = aa;
26. aa = ma;
27. o = aa;
28. ma = g;
29. ma = aa;
30. ma = o;
}
}

Now some questions based on the code:
IF you remove ALL lines that cause compiler or runtime errors:
1. How many lines did you remove? Which ones and why?
2. How many object references are created?
3. How many objects are created?
4. How many objects are eligible for garbage collection after line 30 BEFORE the method exits?
This is not code from a mock exam. Just something I wrote up. I'm not sure of the answer to number 2 myself.
April