There are only few bindings for ObservableList, namely "isEmpty" and "size". While it is nice to have them, complex applications often need more aggregates bindings.

In our experience with JavaFX 8 we identified the frequent request to have "any" and "all" aggregate functions, which allow to ask questions like "Do all / any elements in a list match a predicate?". For example, an application model might provide an observable list of products, lilke the content of a shopping cart, and the GUI shall disable the "order" button in case some of the products are out of stock. This is rather tedious coding in JavaFX 8 as there are no dynamic aggregates.

We have developed a solution for that request which makes it simple to link one-values to multi-values: The "any" and "all" bindings.

        private static final <T> BooleanBinding any(final ObservableList<T> source, final Predicate<T> predicate) {
            return createBooleanBinding(() -> source.stream().anyMatch(predicate), source);
        }

        private static final <T> BooleanBinding all(final ObservableList<T> source, final Predicate<T> predicate) {
            /*
             * Stream.allMatch() (in contrast to Stream.anyMatch() returns 'true' for empty streams, so this has to be checked explicitly.
             */
            return createBooleanBinding(() -> !source.isEmpty() && source.stream().allMatch(predicate), source);
        }

Using these methods it is pretty easy to implement things like "output is true only if list contains only Boolean.TRUE elements".

In fact, it would be rather simple to even extend this solution to also provide "none()" and "reduce(T identity, BinaryOperator<T> accumulator)" bindings, thanks to Stream's "noneMatch" and "reduce" collector functions.

It would be a real help to find these bindings in the fluent API of a future JavaFX version!