On Fri, 9 Dec 2022 18:35:28 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
>> modules/javafx.base/src/main/java/javafx/beans/property/ReadOnlyListProperty.java >> line 119: >> >>> 117: >>> 118: @SuppressWarnings("unchecked") >>> 119: final List<E> list = (List<E>)obj; // safe cast as elements >>> are only referenced >> >> I'm not sure why it's safe to cast to a `List<E>`. You're getting a `List`, >> but it could be a list of something else. In the `Map` and `Set` variants >> there is a try-catch for casting exceptions. > > It's safe as you're never actually using the type `E`, but I suppose the 2nd > list can also be `List<?>` as only `equals` is called on it. The 2nd > `ListIterator` would then also be `ListIterator<?>`. > > Casting to a specific generic type (like `List<E>`) never verifies if all the > elements are of that type, you're just telling the compiler that they are. > > Only when you do something like: > > E e = list.get(0); > > ... you may get a CCE here (but the compiler allowed it because you casted it > to `List<E>` earlier). That's why I say it is safe because the follow up > code does not do any such action (it in fact does `Object o2 = e2.next()` -- > it would be bad if it was `E o2 = e2.next`). > > Looking at it again, I think making the 2nd `List` a `List<?>` is better, as > we don't know yet at that stage that they all are of type `E` (even though it > doesn't matter for the code following it). It also removes the need for the `SuppressWarnings` here. ------------- PR: https://git.openjdk.org/jfx/pull/969