On Wed, 15 Oct 2025 12:08:36 GMT, Michael Strauß <[email protected]> wrote:
>> This PR implements two new default methods on `ObservableList` to be able to
>> replace elements at a given position or within a specified range.
>>
>> Justification for this change is to allow an `ObservableList` to be bulk
>> modified resulting in a single `ListChangeListener` call back. In this way
>> the callbacks don't observe the list changing its size from S to S-X back to
>> S again(*). Currently the only way to bulk replace a range of items is to
>> remove X items then add X items, resulting in two listener callbacks in
>> between which the size of the list can be observed to change.
>>
>> The other alternative is to call `set` individually for each item, which
>> results in many change notifications.
>>
>> With the addition of this PR, and the changes in
>> `ModifiableObservableListBase`, replacing a range of items becomes a single
>> change callback.
>>
>> (*) The list may indeed change size still as plain `List` does not have
>> `setAll` operations; size listeners may observe this, but it will no longer
>> be observable from a `ListChangeListener` due to multiple separate callbacks.
>
> modules/javafx.base/src/main/java/javafx/collections/ObservableList.java line
> 92:
>
>> 90: *
>> 91: * @param index the start index at which to replace elements, must
>> be in
>> 92: * {@code 0 .. size() - col.size()}
>
> This seems to be an unnecessary limitation. It means that as a result of this
> operation, ~~the list can only be shorter, but not longer~~ the size of the
> list must stay the same. The `setAll(int, int, Collection)` overload doesn't
> have this limitation.
Initially, I only wanted to support a "pure" `set` function (to avoid a
`set(int)` loop + notifications), where you can have a range of elements
replaced by another range of the exact same size (so an `int` and `Collection`
is enough to define this). However, there was an open ticket to have a variant
`(from, to, Collection)` which is more powerful, but is not truly a "set"
function anymore IMHO.
I figured I could implement both, but I think having only `set(int,
Collection)` would be sufficient for most use cases.
I suppose it is possible to relax this, but it would have a bit of weird usage
I think:
List.of(A, B, C, D).setAll(1, List.of(E, F, G)) -> A, E, F, G
List.of(A, B, C, D).setAll(2, List.of(E, F, G)) -> A, B, E, F, G
List.of(A, B, C, D).setAll(3, List.of(E, F, G)) -> A, B, C, E, F, G
Now it can also extend the collection, which looks weird. The other
`setAll(from, to, col)` does indeed allow this, but perhaps it shouldn't be
called `setAll` as it is not strictly doing what a loop of `set` calls normally
could be doing...
Perhaps I shouldn't have attempted to reuse an old ticket, and just keep it
simple with only a `setAll(int, Collection)`...
-------------
PR Review Comment: https://git.openjdk.org/jfx/pull/1937#discussion_r2432401418
