Collector / Collectors

[Remi Forax]

On 06/20/2013 06:58 PM, Brian Goetz wrote:
> Spec and implementation:

Brian
if you import java.util.stream.Collectors.CollectorImpl, instead of new 
Collectors.CollectorImpl..., you can write
new CollectorImpl..., which is easier to read.

>
>     /**
>      * Returns a new {@code Collector} described by the given {@code 
> supplier},
>      * {@code accumulator}, and {@code combiner} functions.  The 
> resulting
>      * {@code Collector} has the {@code 
> Collector.Characteristics.IDENTITY_FINISH}
>      * characteristic.
>      *
>      * @param supplier The supplier function for the new collector
>      * @param accumulator The accumulator function for the new collector
>      * @param combiner The combiner function for the new collector
>      * @param <T> The type of input elements for the new collector
>      * @param <R> The type of intermediate accumulation result, and 
> final result,
>      *           for the new collector
>      * @return the new {@code Collector}
>      */
>     static<T, R> Collector<T, R, R> of(Supplier<R> supplier,
>                                        BiConsumer<R, T> accumulator,
>                                        BinaryOperator<R> combiner) {
>         return new Collectors.CollectorImpl<>(supplier, accumulator, 
> combiner, Collectors.CH_ID);
>
>     }
>
>     /**
>      * Returns a new {@code Collector} described by the given {@code 
> supplier},
>      * {@code accumulator}, {@code combiner}, and {@code finisher} 
> functions.
>      *
>      * @param supplier The supplier function for the new collector
>      * @param accumulator The accumulator function for the new collector
>      * @param combiner The combiner function for the new collector
>      * @param <T> The type of input elements for the new collector
>      * @param <A> The intermediate accumulation type of the new collector
>      * @param <R> The final result type of the new collector
>      * @return the new {@code Collector}
>      */
>     static<T, A, R> Collector<T, A, R> of(Supplier<A> supplier,
>                                           BiConsumer<A, T> accumulator,
>                                           BinaryOperator<A> combiner,
>                                           Function<A, R> finisher) {
>         return new Collectors.CollectorImpl<>(supplier, accumulator, 
> combiner, finisher, Collectors.CH_NOID);
>     }

cheers,
Rémi

>
>
>
> On 6/20/2013 12:45 PM, Brian Goetz wrote:
>> Several people have suggested adding:
>>
>>    Collector.of(supplier, accumulator, combiner)
>>    Collector.of(supplier, accumulator, combiner, finisher)
>>
>> which is sensible and easy.
>>
>> On 6/18/2013 11:58 AM, Brian Goetz wrote:
>>> I think I may (finally!) have a final API candidate for Collector /
>>> Collectors.  Updated docs here:
>>>
>>>    http://cr.openjdk.java.net/~briangoetz/doctmp/doc/
>>>
>>> Salient recent changes:
>>>   - Incorporation of finishing function into Collector
>>>   - Renamings in Collector API
>>>   - Morph toStringBuilder, toStringJoiner into joining()
>>>   - Add prefix/suffix version of joining()
>>>   - Addition of summingBy{Int,Long,Double}
>>>   - Addition of averagingBy{Int,Long,Double}
>>>   - Rename toXxxSummaryStatistics to summarizingXxx
>>>   - no-see reducing, and minBy/maxBy collectors return Optional
>>>   - elimination of canned merger functions from API
>>>
>>> Please review the API and spec.  I have set up a SurveyMonkey with the
>>> usual password to collect review comments at:
>>>
>>>    https://www.surveymonkey.com/s/3TTBJ7K
>>>
>>>