| Package | Description | 
|---|---|
| java.util | Contains the collections framework, legacy collection classes, event model,
date and time facilities, internationalization, and miscellaneous utility
classes (a string tokenizer, a random-number generator, and a bit array). | 
| 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 | Method and Description | 
|---|---|
| static <T> Comparator<T> | Comparator. comparingLong(ToLongFunction<? super T> keyExtractor)Accepts a function that extracts a  longsort key from a typeT, and returns aComparator<T>that compares by that
 sort key. | 
| default Comparator<T> | Comparator. thenComparingLong(ToLongFunction<? super T> keyExtractor)Returns a lexicographic-order comparator with a function that
 extracts a  longsort key. | 
| Modifier and Type | Method and Description | 
|---|---|
| long | ConcurrentHashMap. reduceEntriesToLong(long parallelismThreshold,
                   ToLongFunction<Map.Entry<K,V>> transformer,
                   long basis,
                   LongBinaryOperator reducer)Returns the result of accumulating the given transformation
 of all entries using the given reducer to combine values,
 and the given basis as an identity value. | 
| long | ConcurrentHashMap. reduceKeysToLong(long parallelismThreshold,
                ToLongFunction<? super K> transformer,
                long basis,
                LongBinaryOperator reducer)Returns the result of accumulating the given transformation
 of all keys using the given reducer to combine values, and
 the given basis as an identity value. | 
| long | ConcurrentHashMap. reduceValuesToLong(long parallelismThreshold,
                  ToLongFunction<? super V> transformer,
                  long basis,
                  LongBinaryOperator reducer)Returns the result of accumulating the given transformation
 of all values using the given reducer to combine values,
 and the given basis as an identity value. | 
| Modifier and Type | Method and Description | 
|---|---|
| static <T> Collector<T,?,Double> | Collectors. averagingLong(ToLongFunction<? super T> mapper)Returns a  Collectorthat produces the arithmetic mean of a long-valued
 function applied to the input elements. | 
| LongStream | Stream. mapToLong(ToLongFunction<? super T> mapper)Returns a  LongStreamconsisting of the results of applying the
 given function to the elements of this stream. | 
| static <T> Collector<T,?,LongSummaryStatistics> | Collectors. summarizingLong(ToLongFunction<? super T> mapper)Returns a  Collectorwhich applies anlong-producing
 mapping function to each input element, and returns summary statistics
 for the resulting values. | 
| static <T> Collector<T,?,Long> | Collectors. summingLong(ToLongFunction<? super T> mapper)Returns a  Collectorthat produces the sum of a long-valued
 function applied to the input elements. | 
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