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

[Nir Lisker]

On Wed, 15 Oct 2025 03:40:24 GMT, John Hendrikx <jhendrikx 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.

How about doing this through the SubList view? JavaFX's implementation already has a `SubObservableList` inner class that propagates changes on it to the list's listeners:

		ObservableList<Integer> list = FXCollections.observableArrayList();
		list.addAll(0, 1, 2, 3, 4, 5, 6);
		list.addListener((ListChangeListener<Integer>) c -> System.out.println(c));
		List<Integer> subList = list.subList(2, 4);
		System.out.println(list);
		System.out.println(subList);
		subList.clear(); // equivalent to list.remove(2, 4);

prints

[0, 1, 2, 3, 4, 5, 6]
[2, 3]
{ [2, 3] removed at 2 }


 The issue is that it's a `List` and not an `ObservableList`, so it doesn't have JavaFX's additional bulk operation methods. However, "just" having `ObservableList#subList` return an `ObservableList` will allow to make all range operations easily:

		ObservableList<Integer> list = FXCollections.observableArrayList();
		list.addAll(0, 1, 2, 3, 4, 5, 6);
		list.addListener((ListChangeListener<Integer>) c -> System.out.println(c));
		ObservableList<Integer> subList = list.subList(2, 4); // suggestion
		subList.setAll(7, 8);

I think that this would be more flexible/composable and result in a smaller API surface (current bulk methods would also be made redundant technically).

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PR Comment: https://git.openjdk.org/jfx/pull/1937#issuecomment-3405348899