why doesn't code in 2.9 work like in 2.8?

2.8 Does this code compile? If it does, what is its output? class A 1 public class B extends At public static void main(Stringl] args) f Aa=new B(); System.out.println ("works"); works 2.9 Does this code compile? If it does, what is its output? class A th public class B extends Af public static void main(String [] args) B a = new A(); System. out . println("works"); compile error: B.java :5: error: incompatible types: A cannot be converted to B B a = new A(); 1 error