Java Casting Interface to Class

Question

public class InterfaceCasting {

    private static class A{}

    public static void main(String[] args) {
        A a = new A();
        Serializable serializable          


        

Answer 1

The detailed rules for compile-time legality of a casting conversion of a value of compile-time reference type S to a compile-time reference type T are as follows:
[...]
If S is an interface type:
- If T is an array type, [...].
- If T is a type that is not final (§8.1.1), then if there exists a supertype X of T, and a supertype Y of S, such that both X and Y are provably distinct parameterized types, and that the erasures of X and Y are the same, a compile-time error occurs. Otherwise, the cast is always legal at compile time (because even if T does not implement S, a subclass of T might).

Source :
JLS : Conversions and Promotions