Stream (Java)

Stream.md

Intermediate Operation (중간 연산)

Operation	Stateless	Style	Return Type	Parameter	Function Descriptor	Description
filter		Filtering	Stream<T>	Predicate<T>	T -> boolean
distinct	stateful, unbound	Filtering	Stream<T>
sorted	stateful, unbound	Sorting	Stream<T>	Comparator<T>	(T, T) -> int
takeWhile		Slicing	Stream<T>	Predicate<T>	T -> boolean	limit
dropWhile		Slicing	Stream<T>	Predicate<T>	T -> boolean	skip
limit	stateful, bound	Slicing	Stream<T>	long		short circuit
skip	stateful, bound	Slicing	Stream<T>	long
map		Mapping	Stream<T>	Function<T, R>	T -> R
flatMap		Mapping	Stream<T>	Function<T, Stream<R>>	T -> Stream<R>

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Terminal Operation (최종 연산)

Operation	Stateless	Style	Return Type	Parameter	Function Descriptor	Description
anyMatch		Matching	boolean	Predicate<T>	T -> boolean	short circuit
allMatch		Matching	boolean	Predicate<T>	T -> boolean	short circuit
noneMatch		Matching	boolean	Predicate<T>	T -> boolean	short circuit
findAny		Finding	Optional<T>
findFirst		Finding	Optional<T>
forEach		Iteration	void	Consumer<T>	T -> void
collect		Reduce	R	Collector<T, A, R>	Supplier<A> supplier BiConsumer<A, T> accumulator BinaryOperator<A> combiner Function<A, R> finisher
reduce	stateful, bound	Reduce	Optional<T>	BinaryOperator<T>	(T, T) -> T
count		Reduce	long

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Filtering

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
filter	intermediate	Filtering	Stream<T>	Predicate<T>	T -> boolean
distinct	intermediate	Filtering	Stream<T>

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Slicing

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
takeWhile	intermediate	Slicing	Stream<T>	Predicate<T>	T -> boolean	limit
dropWhile	intermediate	Slicing	Stream<T>	Predicate<T>	T -> boolean	skip
limit	intermediate	Slicing	Stream<T>	long		short circuit
skip	intermediate	Slicing	Stream<T>	long

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Mapping

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
map	intermediate	Mapping	Stream<T>	Function<T, R>	T -> R
flatMap	intermediate	Mapping	Stream<T>	Function<T, Stream<R>>	T -> Stream<R>

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Matching

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
anyMatch	terminal	Matching	boolean	Predicate<T>	T -> boolean	short circuit
allMatch	terminal	Matching	boolean	Predicate<T>	T -> boolean	short circuit
noneMatch	terminal	Matching	boolean	Predicate<T>	T -> boolean	short circuit

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Finding

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
findAny	terminal	Finding	Optional<T>			Short Circuit
findFirst	terminal	Finding	Optional<T>			Short Circuit

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Reduce (Fold)

Operation	Operation Type	Style	Return Type	Parameter	Function Descriptor	Description
forEach	terminal	Iteration	void	Consumer<T>	T -> void
collect	terminal	Reduce	R	Collector<T, A, R>	Supplier<A> supplier BiConsumer<A, T> accumulator BinaryOperator<A> combiner Function<A, R> finisher
reduce	termianl	Reduce	Optional<T>	BinaryOperator<T>	(T, T) -> T
count	terminal	Reduce	long

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Collector

interface Collector<T, A, R> {
  Supplier<A> supplier();
  BiConsumer<A, T> accumulator();
  BinaryOperator<A> combiner();
  Function<A, R> finisher();
  Set<Characteristics> characteristics();
}

Static Method	Collector Type (Return Type)	Collect Type (Reduce Type)	Parameter Types
toList	Collector<T, ?, List<T>>	List<T>
toSet	Collector<T, ?, Set<T>>	Set<T>
toCollection	Collector<T, ?, C>	C extends Collection<T>	Supplier<C>
joining	Collector<CharSequence, ?, String>	String	CharSequence delimiter (optional) CharSequence prefix (optional) CharSequence suffix (optional)
counting	Collector<T, ?, Long>	Long
summingInt summingLong summingDouble	Collector<T, ?, Integer> Collector<T, ?, Long> Collector<T, ?, Double>	Integer Long Double	ToIntFunction<? super T> ToLongFunction<? super T> ToDoubleFunction<? super T>
averagingInt averagingLong averagingDouble	Collector<T, ?, Double> Collector<T, ?, Double> Collector<T, ?, Double>	Double Double Double	ToIntFunction<? super T> ToLongFunction<? super T> ToDoubleFunction<? super T>
summarizingInt summarizingLong summarizingDouble	Collector<T, ?, IntSummaryStatistics> Collector<T, ?, LongSummaryStatistics> Collector<T, ?, DoubleSummaryStatistics>	IntSummaryStatistics LongSummaryStatistics DoubleSummaryStatistics	ToIntFunction<? super T> ToLongFunction<? super T> ToDoubleFunction<? super T>
maxBy	Collector<T, ?, Optional<T>>	Optional<T>	Comparator<? super T>
minBy	Collector<T, ?, Optional<T>>	Optional<T>	Comparator<? super T>
mapping	Collector<T, ?, R>	R	Function<? super T, ? extends U> mapper Collector<? super U, A, R> downstream
flatMapping	Collector<T, ?, R>	R	Function<? super T, ? extends Stream<? extends U>> mapper Collector<? super U, A, R> downstream
filtering	Collector<T, ?, R>	R	Predicate<? super T> predicate Collector<? super T, A, R> downstream
reducing	Collector<T, ?, T> Collector<T, ?, Optional<T>> Collector<T, ?, U>	T Optional<T> U	T identity, BinaryOperator<T> op BinaryOperator<T> op U identity, Function<? super T, ? extends U> mapper, BinaryOperator<U> op
collectingAndThen	Collector<T, A, RR>	RR	Collector<T, A, R> downstream, Function<R, RR> finisher
groupingBy	Collector<T, ?, Map<K, List<T>>> Collector<T, ?, Map<K, D>> Collector<T, ?, M>	Map<K, List<T>> Map<K, D> M extends Map<K, D>	Function<? super T, ? extends K> classfier Function<? super T, ? extends K> classfier, Collector<? super T, A, D> downstream Function<? super T, ? extends k> classfier, Supplier<M> mapFactory, Collector<? super T, A, D>
partitioningBy	Collector<T, ?, Map<Boolean, List<T>>> Collector<T, ?, Map<Boolean, D>	Map<Boolean, List<T>> Map<Boolean, D>	Predicate<? super T> predicate Predicate<? super T> predicate, Collector<? super T, A, D> downstream
teeing	Collector<T, ?, R>	R	Collector<? super T, ?, R1> downstream1, Collector<? super T, ?, R2> downstream2, BiFunction<? super R1, ? super R2, R> merger

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Parallel Stream

https://n1tjrgns.tistory.com/292

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Comparator

public interface Comparator<T> {
  int compare(T o1, T o2);
}

Static Method	Parameter Types	Return Type
comparing	Function<? super T, ? extends U> keyExtractor, Comparator<? super U> keyComparator (optional)	Comparator<T>
comparingInt comparingLong comparingDouble	ToIntFunction<? super T> keyExtractor ToLongFunction<? super T> keyExtractor ToDoubleFunction<? super T> keyExtractor	Comparator<T>
naturalOrder		Comparator<T>
reverseOrder		Comparator<T>
nullsFirst	Comparator<? super T> comparator	Comparator<T>
nullsLast	Comparator<? super T> comparator	Comparator<T>