no.digipost

Class DiggCollectors

java.lang.Object

no.digipost.DiggCollectors

public final class DiggCollectors
extends Object

Various Collector implementations.

Method Summary

Modifier and Type	Method and Description
static <T,A,R> AdaptableCollector<T,A,R>	adapt(Collector<T,A,R> collector) Turn any Collector into an AdaptableCollector.
static <T> AdaptableCollector<T,OneTimeAssignment<T>,Optional<T>>	allowAtMostOne() This is a collector for accessing the expected only element of a Stream, as it will throw an exception if more than one element is processed.
static <T1,T2> AdaptableCollector<ViewableAsTuple<T1,Optional<T2>>,?,Map<T1,List<T2>>>	toMultimap() A multimap maps from keys to lists, and this collector will arrange tuples by putting each distinct first tuple-element as keys of the resulting map, mapping them to a List, and adding each second tuple-element to the list.
static <T,K,V> AdaptableCollector<T,?,Map<K,List<V>>>	toMultimap(Function<? super T,K> keyExtractor, Function<? super T,Optional<V>> extractor)
static <T,V> AdaptableCollector<T,?,Map<T,List<V>>>	toMultimap(Function<? super T,Optional<V>> extractor)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

toMultimap

public static <T1,T2> AdaptableCollector<ViewableAsTuple<T1,Optional<T2>>,?,Map<T1,List<T2>>> toMultimap()

A multimap maps from keys to lists, and this collector will arrange tuples by putting each distinct first tuple-element as keys of the resulting map, mapping them to a List, and adding each second tuple-element to the list.

Type Parameters:

T1 - The type of the first tuple element, which will become the key type of the resulting Map.

T2 - The type of the second tuple element, which will become the List<T2> value type of the resulting Map.

Returns:

the multimap collector.

toMultimap

public static <T,V> AdaptableCollector<T,?,Map<T,List<V>>> toMultimap(Function<? super T,Optional<V>> extractor)

toMultimap

public static <T,K,V> AdaptableCollector<T,?,Map<K,List<V>>> toMultimap(Function<? super T,K> keyExtractor,
                                                                        Function<? super T,Optional<V>> extractor)

allowAtMostOne

public static <T> AdaptableCollector<T,OneTimeAssignment<T>,Optional<T>> allowAtMostOne()

This is a collector for accessing the expected only element of a Stream, as it will throw an exception if more than one element is processed. This should be used in preference of the Stream.findFirst() or Stream.findAny() when it is imperative that the stream indeed yields a maximum of one single element, and any more elements is considered a programming error.

Returns:

the collector

adapt

public static <T,A,R> AdaptableCollector<T,A,R> adapt(Collector<T,A,R> collector)

Turn any Collector into an AdaptableCollector.

Parameters:

collector - the collector to convert

Returns:

the AdaptableCollector

See Also:

AdaptableCollector