On Fri, 9 Dec 2022 17:47:33 GMT, Nir Lisker <nlis...@openjdk.org> wrote:
>> John Hendrikx has updated the pull request incrementally with one additional
>> commit since the last revision:
>>
>> Revert renames in Disposer
>
> 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).
-------------
PR: https://git.openjdk.org/jfx/pull/969
