Collector / Collectors

[Brian Goetz]

Spec and implementation:

     /**
      * 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);
     }



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
>>
>>