Why is no unchecked cast warning given when downcasting Throwable to Exception?

Using this code:

public class DowncastTest {
    public static void main(String[] args) {
        try {
            System.out.println(1);
        } catch (Exception ex) {
            Throwable cause = ex.getCause();
            if (cause != null) {
                Exception exCause = (Exception)cause;
                System.out.println(exCause);
            }
        }
    }
}

Why does the javac not give an unchecked cast warning?

Exception extends Throwable, so you cannot just convert all Throwables to an Exception.

Why does the javac not give an unchecked cast warning?

Because there are no generics involved. I don't think "unchecked cast" means what you think it means. It's for situations like:

List<?> list = getListFromSomewhere();
List<String> strings = (List<String>) list;

This is an unchecked cast, because the cast to List<String> doesn't really check whether list refers to a List<String>... it can't do, as there's no such concept at execution time.

The cast you've got at the moment from Throwable to Exception is just a normal cast - it will throw a ClassCastException if cause is a reference to an object which is not an Exception (or subclass).