Inheritance tree and interfaces

Question

Hello!
Interface is not a part of inheritance tree. It means, that the next code is absolutely legal:
class App{
       public static void main(String... args){
                Bar bar = (Bar)new Foo();
class Foo{}
interface Bar{}You can compile it, run and get a ClassCastException.
But if I write it so:
final class Foo{}
...I'll get compilation error.
I know how it works, but I don't understand why.
Does anybody have any ideas?

Answer 1

Ataraxisme++.
Cue JLS :
JLS sayz (emphasis added):
5.1.6 Narrowing Reference Conversions
The following conversions are called the narrowing reference conversions :
❋ From any reference type S to any reference type T, provided that S is a proper supertype (§4.10) of T. (An important special case is that there is a
narrowing conversion from the class type Object to any other reference type.)
❋ From any class type C to any non-parameterized interface type K, provided that C is not final and does not implement K.
❋ From any interface type J to any non-parameterized class type C that is not final.
❋ From the interface types Cloneable and java.io.Serializable to any array type T[].
❋ From any interface type J to any non-parameterized interface type K, provided that J is not a subinterface of K.
❋ From any array type SC[] to any array type TC[], provided that SC and TC are reference types and there is a narrowing conversion from SC to TC.
Such conversions require a test at run time to find out whether the actual reference value is a legitimate value of the new type. If not, then a ClassCastException is thrown.