On Fri, 9 Dec 2022 18:35:28 GMT, John Hendrikx <[email protected]> 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
