+1
I was tempted to saying something more about an associated value if it was not
operated on (accumulated and combined), but that’s probably api note territory.
Paul.
> On 8 Dec 2016, at 14:48, Stuart Marks <stuart.ma...@oracle.com> wrote:
>
> Hi all,
>
> Please review this small spec change to the Collectors.partitioningBy()
> methods, appended below. This collector returns Map<Boolean, Something>. The
> change requires the implementation always to populate the returned map with
> entries for both false and true keys.
>
> The implementation already does this; the entries are initially populated
> with values obtained by calling the supplier of the downstream collector.
>
> The reason for this spec change that it's useful for applications to be able
> to rely on this. The spec is currently silent about what entries will be
> present in the map. If one or the other (or both!) of the entries can be
> absent, callers would have to defend against this possibility. For example,
>
> Map<Boolean, List<V>> map = stream.collect(partitioningBy(pred));
> processResults(map.getOrDefault(false, List.of()),
> map.getOrDefault(true, List.of()));
>
> With the guarantee, it's safe instead to write:
>
> Map<Boolean, List<V>> map = stream.collect(partitioningBy(pred));
> processResults(map.get(false), map.get(true));
>
> In fact, this code works today, it's just that it's not specified to work. It
> should be.
>
> Thanks,
>
> s'marks
>
>
>
> diff -r 7583c87dfe7c
> src/java.base/share/classes/java/util/stream/Collectors.java
> --- a/src/java.base/share/classes/java/util/stream/Collectors.java Thu Dec
> 08 21:21:39 2016 +0000
> +++ b/src/java.base/share/classes/java/util/stream/Collectors.java Thu Dec
> 08 14:39:31 2016 -0800
> @@ -1268,6 +1268,8 @@
> * to a {@code Predicate}, and organizes them into a
> * {@code Map<Boolean, List<T>>}.
> *
> + * The returned {@code Map} always contains mappings for both
> + * {@code false} and {@code true} keys.
> * There are no guarantees on the type, mutability,
> * serializability, or thread-safety of the {@code Map} or {@code List}
> * returned.
> @@ -1290,7 +1292,10 @@
> * {@code Map<Boolean, D>} whose values are the result of the downstream
> * reduction.
> *
> - * <p>There are no guarantees on the type, mutability,
> + * <p>
> + * The returned {@code Map} always contains mappings for both
> + * {@code false} and {@code true} keys.
> + * There are no guarantees on the type, mutability,
> * serializability, or thread-safety of the {@code Map} returned.
> *
> * @param <T> the type of the input elements
