Rules for casting generics type

Question

I know that there is a section in jsr14 spec about rules of casting generic types, but it seems outdated with
JLS3.
It is obvious that e.g. Class<String> cannot be casted to Class<Integer>.
However in
<T,V> void foo (Class<T> ct) {
Class<V> cv = (Class<V>)ct;
The cast is permitted by the compiler though of course marked as unchecked (The cast should be rejected according to jsr14 spec since none of the types is a subtype of the other).
So the question is: what are the rules, compiler uses to check casts?

Answer 1

1. There is an (unsafe) explicit cast from l1 to l2.
2. There is an implicit cast in the last line, because
l2 is a List<String>, the line is compiled to the
equivalent of
System.out.println(" result:" + (String) l2.get(0));
// ClassCastException: java.lang.String