| Package | Description | 
|---|---|
| java.util.concurrent | Utility classes commonly useful in concurrent programming. | 
| java.util.stream | Classes to support functional-style operations on streams of elements, such
 as map-reduce transformations on collections. | 
| Modifier and Type | Interface and Description | 
|---|---|
| interface  | ConcurrentNavigableMap<K,V>A  ConcurrentMapsupportingNavigableMapoperations,
 and recursively so for its navigable sub-maps. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | ConcurrentHashMap<K,V>A hash table supporting full concurrency of retrievals and
 high expected concurrency for updates. | 
| class  | ConcurrentSkipListMap<K,V>A scalable concurrent  ConcurrentNavigableMapimplementation. | 
| Modifier and Type | Method and Description | 
|---|---|
| static <T,K,A,D,M extends ConcurrentMap<K,D>> | Collectors. groupingByConcurrent(Function<? super T,? extends K> classifier,
                    Supplier<M> mapFactory,
                    Collector<? super T,A,D> downstream)Returns a concurrent  Collectorimplementing a cascaded "group by"
 operation on input elements of typeT, grouping elements
 according to a classification function, and then performing a reduction
 operation on the values associated with a given key using the specified
 downstreamCollector. | 
| static <T,K,U,M extends ConcurrentMap<K,U>> | Collectors. toConcurrentMap(Function<? super T,? extends K> keyMapper,
               Function<? super T,? extends U> valueMapper,
               BinaryOperator<U> mergeFunction,
               Supplier<M> mapSupplier)Returns a concurrent  Collectorthat accumulates elements into aConcurrentMapwhose keys and values are the result of applying
 the provided mapping functions to the input elements. | 
| Modifier and Type | Method and Description | 
|---|---|
| static <T,K> Collector<T,?,ConcurrentMap<K,List<T>>> | Collectors. groupingByConcurrent(Function<? super T,? extends K> classifier)Returns a concurrent  Collectorimplementing a "group by"
 operation on input elements of typeT, grouping elements
 according to a classification function. | 
| static <T,K,A,D> Collector<T,?,ConcurrentMap<K,D>> | Collectors. groupingByConcurrent(Function<? super T,? extends K> classifier,
                    Collector<? super T,A,D> downstream)Returns a concurrent  Collectorimplementing a cascaded "group by"
 operation on input elements of typeT, grouping elements
 according to a classification function, and then performing a reduction
 operation on the values associated with a given key using the specified
 downstreamCollector. | 
| static <T,K,U> Collector<T,?,ConcurrentMap<K,U>> | Collectors. toConcurrentMap(Function<? super T,? extends K> keyMapper,
               Function<? super T,? extends U> valueMapper)Returns a concurrent  Collectorthat accumulates elements into aConcurrentMapwhose keys and values are the result of applying
 the provided mapping functions to the input elements. | 
| static <T,K,U> Collector<T,?,ConcurrentMap<K,U>> | Collectors. toConcurrentMap(Function<? super T,? extends K> keyMapper,
               Function<? super T,? extends U> valueMapper,
               BinaryOperator<U> mergeFunction)Returns a concurrent  Collectorthat accumulates elements into aConcurrentMapwhose keys and values are the result of applying
 the provided mapping functions to the input elements. | 
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