On Tue, 22 Sep 2026 00:04:33 GMT, Michael Strauß <[email protected]> wrote:
>> John Hendrikx has updated the pull request incrementally with one additional
>> commit since the last revision:
>>
>> Implement notifying boolean
>
> modules/javafx.base/src/main/java/javafx/beans/value/ObservableListValue.java
> line 36:
>
>> 34: * {@link ObservableValue}. A {@code ChangeListener} registered on an
>> 35: * {@code ObservableListValue} is notified when the contents of the list
>> change
>> 36: * as well as when the list reference is replaced. When the contents
>> change, the
>
> I think that invoking a change listener when only the _contents_ of a list
> has changed is a jarring defect. A change listener should only be invoked
> when the list instance is changed; for its contents, we have
> `ListChangeListener`. Now, I'm not sure if we can ever fix this, but maybe we
> shouldn't enshrine this defect into specification with this PR. If we come to
> the conclusion that it can't be changed, we can always specify this behavior
> later.
Hm, yeah, I doubt we'll ever be able to change it, and I would recommend
deprecating them completely. But since this was already a bit out of scope for
this PR, I can just leave this change out.
A closer (unrelated) investigation also turned up that any kind of nested
change on an `ObservableList` will break the `Change` you receive, even if you
trigger that nested change from an invalidation or change listener (ie. before
`ListChangeListener`s are called).
So I think I would also recommend throwing a `ConcurrentModificationException`
in those cases, because the `Change` you receive in a nested scenario will just
be incorrect, lead to perhaps `IndexOutOfBoundsException`s or worse still,
silent corruption as you process the outdated `Change`.
I was checking this to see if it would at some point be useful to have
`ListenerManager` support the collection observables, but the whole nested
change part won't apply for those as it is disallowed (hidden on
`ListChangeListener` but applies to all types of listeners for the collection
observables):
* <b>Warning:</b> This class directly accesses the source list to acquire
information about the changes.
* <br> This effectively makes the Change object invalid when another
change occurs on the list.
* <br> For this reason it is <b>not safe to use this class on a different
thread</b>.
* <br> It also means <b>the source list cannot be modified inside the
listener</b> since that would invalidate this Change object
* for all subsequent listeners.
The "inside the listener" should really be "inside any listener on this
observable"...
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PR Review Comment: https://git.openjdk.org/jfx/pull/1081#discussion_r4112159755
