Client and backend. This class is shared: the same code is compiled into your app and into your server, so everything on this page works in both.
public final class Collectors
- Object
- Collectors
The common Collectors: into collections, maps, strings, groups and
numbers.
The results are the JDK’s: groupingBy answers a HashMap of
ArrayLists unless told otherwise, toMap refuses a second value for a
key unless given a function to merge them, and the unmodifiable variants
refuse null.
Every function here is a class of its own, made only by the method that needs it, so an application carries the collectors it uses and no others.
Methods
Inherited methods
Method details
toCollection
public static <T, C extends Collection<T>> Collector<T, ?, C> toCollection(Supplier<C> collectionFactory)toList
public static <T> Collector<T, ?, List<T>> toList()toUnmodifiableList
public static <T> Collector<T, ?, List<T>> toUnmodifiableList()toSet
public static <T> Collector<T, ?, Set<T>> toSet()toUnmodifiableSet
public static <T> Collector<T, ?, Set<T>> toUnmodifiableSet()joining
public static Collector<CharSequence, ?, String> joining()joining
public static Collector<CharSequence, ?, String> joining(CharSequence delimiter)joining
public static Collector<CharSequence, ?, String> joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)mapping
public static <T, U, A, R> Collector<T, ?, R> mapping(Function<? super T, ? extends U> mapper, Collector<? super U, A, R> downstream)filtering
public static <T, A, R> Collector<T, ?, R> filtering(Predicate<? super T> predicate, Collector<? super T, A, R> downstream)flatMapping
public static <T, U, A, R> Collector<T, ?, R> flatMapping(Function<? super T, ? extends Stream<? extends U>> mapper, Collector<? super U, A, R> downstream)collectingAndThen
public static <T, A, R, RR> Collector<T, A, RR> collectingAndThen(Collector<T, A, R> downstream, Function<R, RR> finisher)counting
public static <T> Collector<T, ?, Long> counting()summingInt
public static <T> Collector<T, ?, Integer> summingInt(ToIntFunction<? super T> mapper)summingLong
public static <T> Collector<T, ?, Long> summingLong(ToLongFunction<? super T> mapper)summingDouble
public static <T> Collector<T, ?, Double> summingDouble(ToDoubleFunction<? super T> mapper)averagingInt
public static <T> Collector<T, ?, Double> averagingInt(ToIntFunction<? super T> mapper)averagingLong
public static <T> Collector<T, ?, Double> averagingLong(ToLongFunction<? super T> mapper)averagingDouble
public static <T> Collector<T, ?, Double> averagingDouble(ToDoubleFunction<? super T> mapper)summarizingInt
public static <T> Collector<T, ?, IntSummaryStatistics> summarizingInt(ToIntFunction<? super T> mapper)summarizingLong
public static <T> Collector<T, ?, LongSummaryStatistics> summarizingLong(ToLongFunction<? super T> mapper)summarizingDouble
public static <T> Collector<T, ?, DoubleSummaryStatistics> summarizingDouble(ToDoubleFunction<? super T> mapper)reducing
public static <T> Collector<T, ?, T> reducing(T identity, BinaryOperator<T> op)reducing
public static <T> Collector<T, ?, Optional<T>> reducing(BinaryOperator<T> op)reducing
public static <T, U> Collector<T, ?, U> reducing(U identity, Function<? super T, ? extends U> mapper, BinaryOperator<U> op)minBy
public static <T> Collector<T, ?, Optional<T>> minBy(Comparator<? super T> comparator)maxBy
public static <T> Collector<T, ?, Optional<T>> maxBy(Comparator<? super T> comparator)groupingBy
public static <T, K> Collector<T, ?, Map<K, List<T>>> groupingBy(Function<? super T, ? extends K> classifier)groupingBy
public static <T, K, A, D> Collector<T, ?, Map<K, D>> groupingBy(Function<? super T, ? extends K> classifier, Collector<? super T, A, D> downstream)groupingBy
public static <T, K, D, A, M extends Map<K, D>> Collector<T, ?, M> groupingBy(Function<? super T, ? extends K> classifier, Supplier<M> mapFactory, Collector<? super T, A, D> downstream)partitioningBy
public static <T> Collector<T, ?, Map<Boolean, List<T>>> partitioningBy(Predicate<? super T> predicate)partitioningBy
public static <T, D, A> Collector<T, ?, Map<Boolean, D>> partitioningBy(Predicate<? super T> predicate, Collector<? super T, A, D> downstream)toMap
public static <T, K, U> Collector<T, ?, Map<K, U>> toMap(Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper)toMap
public static <T, K, U> Collector<T, ?, Map<K, U>> toMap(Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper, BinaryOperator<U> mergeFunction)toMap
public static <T, K, U, M extends Map<K, U>> Collector<T, ?, M> toMap(Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper, BinaryOperator<U> mergeFunction, Supplier<M> mapFactory)toUnmodifiableMap
public static <T, K, U> Collector<T, ?, Map<K, U>> toUnmodifiableMap(Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper)toUnmodifiableMap
public static <T, K, U> Collector<T, ?, Map<K, U>> toUnmodifiableMap(Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper, BinaryOperator<U> mergeFunction)