RFR: 8091429: ObservableList<E>#setAll(int from, int to, Collection<? extends E> col)

[John Hendrikx]

On Wed, 15 Oct 2025 12:08:36 GMT, Michael Strauß <mstrauss at openjdk.org> 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)`...

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PR Review Comment: https://git.openjdk.org/jfx/pull/1937#discussion_r2432401418