The JavaFX collections framework offers the `FXCollections.concat(ObservableList...)` method, which creates a new modifiable list that contains a concatenated snapshot of the source lists, backed by an `ArrayList`. However, when the source lists are changed, the concatenated list is not updated.
I propose to add `FXCollections.concatenatedObservableList(ObservableList...)`, which creates an unmodifiable collection view onto the source lists that represents the concatenation of all source elements. When any of the source lists are changed, the change is also reflected in the concatenated view. This would add a useful capability to the JavaFX collections framework which has been requested a number of times [0] [1], and is currently only available via a third-party library [2]. A draft PR is available here: https://github.com/openjdk/jfx/pull/1087 [0] https://stackoverflow.com/questions/37524662/how-to-concatenate-observable-lists-in-javafx [1] https://bugs.openjdk.org/browse/JDK-8164626 [2] https://github.com/tobiasdiez/EasyBind#concat-lists-of-observable-lists
