Jdk8-java Streams Collector

CollectorsThe class contains many common aggregation operations, such as accumulating into a collection, string concatenation, shrinking, and other summary calculations, and creating a summary table (through groupingBy() ).

Built-in collectors

Collecting Device	Behavior
toList()	Collects elements into one List .
toSet()	Collects elements into one Set .
toCollection(Supplier<Collection>)	Collects elements into a specific type Collection .
toMap(Function<T, K>, Function<T, V>)	The elements are collected into one Map , and the elements are converted to key values according to the mapping function provided.
summingInt(ToIntFunction<T>)	Calculates the sum of the int results that are applied to each element (and to the version) of the provided value mapping function long double .
summarizingInt(ToIntFunction<T>)	Calculates the,,,,,,,, int long double sum min max ,, count and average .
reducing()	Apply a reduction to an element (typically used as a downstream collector, for example groupingBy ) (various versions).
partitioningBy(Predicate<T>)	The elements are divided into two groups: the expected groups that are provided for them are retained and the expected groups are not retained.
partitioningBy(Predicate<T>, Collector)	Partitions an element, using the specified downstream collector to process each partition.
groupingBy(Function<T,U>)	Groups elements into one Map , where the key is the provided function applied to the flow element, and the value is the list of elements that share the key.
groupingBy(Function<T,U>, Collector)	Groups the elements, using the specified downstream collector to handle the values associated with each group.
minBy(BinaryOperator<T>)	Calculates the minimum value of the element (same as the maxBy() same).
mapping(Function<T,U>, Collector)	Applies the provided mapping function to each element and processes it using the specified downstream collector (typically used as the downstream collector itself, for example groupingBy ).
joining()	Assuming that the elements are String types, the elements are joined to a string (perhaps using separators, prefixes, and suffixes).
counting()	Calculates the number of elements. (typically used as a downstream collector.) ）

Jdk8-java Streams Collector