CHEATSHEET.md

StreamEx Cheatsheet

Contents

• Glossary
• Stream sources
• New intermediate operations
  • filtering
  • mapping
  • flat-mapping
  • distinct
  • sorting
  • partial reduction
  • concatenate
  • peek
  • misc
• New terminal operations
  • Collector shortcuts
  • Search
  • Folding
  • Primitive operations
  • forEach-like operations
  • misc
• Collectors
  • Basic collectors
  • Adaptor collectors

Glossary

• any: either of StreamEx, IntStreamEx, LongStreamEx, DoubleStreamEx, EntryStream, sometimes without EntryStream.
• element: any object or primitive value which appears in the stream pipeline.
• entry: a pair of objects usually (but not always) having the Map.Entry semantics. The first object in the pair is key, the second one is value.

Stream sources

What I want	How to get it
Empty Stream	any.empty()
Stream of array, varargs, Collection, Spliterator, Iterator, Stream	any.of()
Stream of Enumeration	StreamEx.of()
Stream of array or List elements in reverse order	StreamEx.ofReversed()
Stream of boxed Collection<Integer>, etc. with unboxing	IntStreamEx/LongStreamEx/DoubleStreamEx.of()
Stream of boxed array Integer[], etc. with unboxing	IntStreamEx/LongStreamEx/DoubleStreamEx.of()
Stream of byte[], char[], short[] array	IntStreamEx.of()
Stream of float[] array	DoubleStreamEx.of()
Infinite Stream from Supplier	any.generate()
Infinite Stream using iterative function	any.iterate()
Convert three-argument for loop to Stream	any.iterate()
Fixed length Stream of constant elements	any.constant()
Stream from mutable object which is left in the known state after full Stream consumption	any.produce()
Custom stream source which maintains mutable state	Emitter/IntEmitter/LongEmitter/DoubleEmitter
Stream of array or List with indices	EntryStream.of()
Stream of single value or empty if null supplied	StreamEx.ofNullable()
Stream of Map keys (with optional values filter)	StreamEx.ofKeys()
Stream of Map values (with optional keys filter)	StreamEx.ofValues()
Stream of Map entries or explicit key-value pairs	EntryStream.of()
Zip two arrays or lists	any.zip()
Split CharSequence with regexp	StreamEx.split()
Stream of List subLists of fixed length	StreamEx.ofSubLists()
Stream of all elements of tree-like structure	StreamEx.ofTree()
Stream of all elements of tree-like structure tracking the elements depth	EntryStream.ofTree()
Stream of all possible pairs of array or List elements	StreamEx/EntryStream.ofPairs()
Stream of all possible tuples of given length of Collection elements	StreamEx.cartesianPower()
Stream of all possible tuples of given Collection of collections	StreamEx.cartesianProduct()
Stream of permutations	StreamEx.ofPermutations()
Stream of combinations	StreamEx.ofCombinations()
Stream of array or List indices (with optional element filter)	IntStreamEx.ofIndices()
Stream of range of integral values (with optional step parameter)	IntStreamEx/LongStreamEx.range()/rangeClosed()
Stream of increasing int or long values	IntStreamEx.ints()/LongStreamEx.longs()
Stream of random numbers	IntStreamEx/LongStreamEx/DoubleStreamEx.of(Random, ...)
Stream of CharSequence symbols	IntStreamEx.ofChars()/ofCodePoints()
Stream of BitSet true bits	IntStreamEx.of(BitSet)
Stream of lines from file or Reader	StreamEx.ofLines()
Stream of bytes from the InputStream	IntStreamEx.of(InputStream)
Stream of ints from the IntBuffer	IntStreamEx.of(IntBuffer)
Stream of longs from the LongBuffer	LongStreamEx.of(LongBuffer)
Stream of doubles from the DoubleBuffer	DoubleStreamEx.of(DoubleBuffer)

New intermediate operations

filtering

What I want	How to get it
Remove nulls	StreamEx/EntryStream.nonNull()
Remove entries whose keys or values are null	EntryStream.nonNullKeys()/nonNullValues()
Remove entries whose keys are equal to any of the supplied keys	EntryStream.withoutKeys()
Remove entries whose values are equal to any of the supplied values	EntryStream.withoutValues()
Remove elements by predicate	any.remove()
Remove given elements	StreamEx/IntStreamEx/LongStreamEx.without()
Remove by value extracted by supplied mapper function	StreamEx.removeBy()
Leave only elements greater/less/at least/at most given value	IntStreamEx/LongStreamEx/DoubleStreamEx.greater()/atLeast()/less()/atMost()
Filter by value extracted by supplied mapper function	StreamEx.filterBy()
Filter entries which keys or values satisfy the predicate	EntryStream.filterKeys()/filterValues()
Filter entries applying the BiPredicate to key and value	EntryStream.filterKeyValue()
Remove entries which keys or values satisfy the predicate	EntryStream.removeKeys()/removeValues()
Remove entries applying the BiPredicate to key and value	EntryStream.removeKeyValue()
Select elements which are instances of given class	StreamEx.select()
Select entries which keys or values are instances of given class	EntryStream.selectKeys()/selectValues()
Take stream elements while the condition is true	any.takeWhile()
Take stream elements while the condition is true including first violating element	any.takeWhileInclusive()
Skip stream elements while the condition is true	any.dropWhile()

mapping

What I want	How to get it
Map array or List indices to the corresponding elements	IntStreamEx.elements()
Map element to the entry	any.mapToEntry()
Map entry keys leaving values unchanged	EntryStream.mapKeys()/mapToKey()
Map entry values leaving keys unchanged	EntryStream.mapValues()/mapToValue()
Map entry key and value using BiFunction	EntryStream.mapKeyValue()
Swap entry key and value (so entry value becomes key and vice versa)	EntryStream.invert()
Drop entry values leaving only keys	EntryStream.keys()
Drop entry keys leaving only values	EntryStream.values()
Convert every entry to String	EntryStream.join()
Map pair of adjacent elements to the single element	any.pairMap()
Map only first or last element, leaving others as is	any.mapFirst()/mapLast()
Map stream element providing special mapper function for the first or last element	any.mapFirstOrElse()/mapLastOrElse()
Attach the first stream element to every stream element	StreamEx.withFirst()
Map only part of input elements using partial function which returns Optional	StreamEx.mapPartial(); EntryStream.mapToKeyPartial()/mapToValuePartial()/mapKeyValuePartial()

flat-mapping

What I want	How to get it
Flat-map primitive stream to the stream of other type	IntStreamEx/LongStreamEx/DoubleStreamEx. flatMapToInt()/flatMapToLong()/flatMapToDouble()/flatMapToObj()
Flat-map stream in a push-like manner	StreamEx/EntryStream. mapMulti()/mapMultiToInt()/mapMultiToLong()/mapMultiToDouble()
Flatten multiple collections to the stream of their elements	StreamEx/EntryStream.flatCollection()
Flatten multiple arrays to the stream of their elements	StreamEx/EntryStream.flatArray()
Flatten multiple maps to the stream of their entries	StreamEx.flatMapToEntry()
Perform cross product of current stream with given array, Collection or Stream source creating entries	StreamEx.cross()
Flat-map entry keys leaving values unchanged	EntryStream.flatMapKeys()/flatMapToKey()
Flat-map entry values leaving keys unchanged	EntryStream.flatMapValues()/flatMapToValue()
Flat-map entry key and value using BiFunction	EntryStream.flatMapKeyValue()

distinct

What I want	How to get it
Leave only distinct elements which appear at least given number of times	StreamEx.distinct(atLeast)
Leave distinct elements using custom key extractor	StreamEx/EntryStream.distinct(keyExtractor)
Leave only entries having distinct keys	EntryStream.distinctKeys()
Leave only entries having distinct values	EntryStream.distinctValues()

sorting

What I want	How to get it
Sort in reverse order	any.reverseSorted()
Sort using given key	any.sortedBy()/sortedByInt()/sortedByLong()/sortedByDouble()

partial reduction

Partial reduction is a procedure of combining several adjacent stream elements. Usually BiPredicate is used to determine which elements should be combined. BiPredicate is applied to the pair of adjacent elements and returns true if they should be combined.

What I want	How to get it
Group some adjacent stream elements into List	StreamEx.groupRuns()
Reduce some adjacent stream elements using Collector or BinaryOperator	StreamEx.collapse()
Collapse some adjacent stream elements into interval	StreamEx.intervalMap()
Remove adjacent duplicate elements counting them	StreamEx.runLengths()
Group adjacent entries with equal keys	EntryStream.collapseKeys()

concatenate

What I want	How to get it
Add new elements/Collection/Stream to the end of existing stream	any.append()
Add new elements/Collection/Stream to the beginning of existing stream	any.prepend()

peek

What I want	How to get it
Peek only entry keys	EntryStream.peekKeys()
Peek only entry values	EntryStream.peekValues()
Peek entry keys and values using BiConsumer	EntryStream.peekKeyValue()
Peek only first or last stream element	any.peekFirst()/peekLast()

misc intermediate operations

What I want	How to get it
Extract first stream element and use it to alternate the rest of the stream	StreamEx.headTail()
Define almost any custom intermediate operation recursively	StreamEx.headTail()
Execute custom-defined operation in fluent manner	any.chain()
Perform parallel stream computation using the custom ForkJoinPool	any.parallel(pool)
Zip two streams together	StreamEx.zipWith()
Get the stream of cumulative prefixes	any.prefix()/EntryStream.prefixKeys()/EntryStream.prefixValues()
Intersperse the stream with given delimiters	any.intersperse()
Replace the stream contents if the stream is empty	StreamEx.ifEmpty()/EntryStream.ifEmpty()

New terminal operations

Collector shortcuts

What I want	How to get it
Collect elements to List, Set or custom Collection	StreamEx/EntryStream.toList()/toSet()/toCollection()
Collect elements to Collection adding custom final step	StreamEx/EntryStream.toListAndThen()/toSetAndThen()/toCollectionAndThen()
Collect elements to immutable List or Set	StreamEx/EntryStream.toImmutableList()/toImmutableSet()
Collect elements to mutable List or Set	StreamEx/EntryStream.toMutableList()/toMutableSet()
Collect elements or entries to Map	StreamEx/EntryStream.toMap()/toSortedMap()/toNavigableMap()
Collect stream of values to Map	StreamEx.valuesToMap()/valuesToSortedMap()/valuesToNavigableMap()
Collect entries to immutable Map	EntryStream.toImmutableMap()
Collect entries to Map adding custom final step	EntryStream.toMapAndThen()
Collect entries to custom Map	EntryStream.toCustomMap()
Partition elements using the Predicate	StreamEx.partitioningBy()/partitioningTo()
Grouping elements	StreamEx.groupingBy()/groupingTo()
Grouping entries	EntryStream.grouping()/groupingTo()
Joining elements to String	any.joining()
Flatten collections and collect them to single final collection	StreamEx.toFlatList()/toFlatCollection()
Getting maximal element using custom key extractor	any.maxBy()/maxByInt()/maxByLong()/maxByDouble()
Getting minimal element using custom key extractor	any.minBy()/minByInt()/minByLong()/minByDouble()

Search

What I want	How to get it
Check whether stream has given element	StreamEx/EntryStream/IntStreamEx/LongStreamEx.has()
Find element satisfying the predicate	any.findFirst(Predicate)/findAny(Predicate)
Find the index of element satisfying the predicate or equal to given value	any.indexOf()

Folding

What I want	How to get it
Fold elements left-to-right	any.foldLeft()
Fold elements right-to-left	StreamEx/EntryStream.foldRight()
Get List of cumulative prefixes or suffixes	StreamEx/EntryStream.scanLeft()/scanRight()
Get primitive array of cumulative prefixes	IntStreamEx/LongStreamEx/DoubleStreamEx.scanLeft()
Reduce elements possibly short-circuiting the reduction	StreamEx/EntryStream.reducingWithZero()

Primitive operations

What I want	How to get it
Collect IntStreamEx to byte[], char[] or short[]	IntStreamEx.toByteArray()/toCharArray()/toShortArray()
Collect IntStreamEx to BitSet	IntStreamEx.toBitSet()
Collect DoubleStreamEx to float[]	DoubleStreamEx.toFloatArray()
Collect stream of chars or codepoints to String	IntStreamEx.charsToString()/codePointsToString()

forEach-like operations

What I want	How to get it
Perform operation on every adjacent pair of elements	StreamEx.forPairs()
Perform operation on entry key and value using BiConsumer	EntryStream.forKeyValue()

misc terminal operations

What I want	How to get it
Convert IntStreamEx to InputStream	IntStreamEx.asByteInputStream()
Drain stream content into the existing Collection	StreamEx.into()
Drain stream content into the existing Map	EntryStream.into()

Collectors

Basic collectors

What I want	How to get it
Collect to array	MoreCollectors.toArray()
Collect to boolean array using the Predicate applied to each element	MoreCollectors.toBooleanArray()
Collect to EnumSet	MoreCollectors.toEnumSet()
Collect Map.Entry entries to map	MoreCollectors.entriesToMap()
Collect Map.Entry entries to custom Map implementation	MoreCollectors.entriesToCustomMap()
Count number of distinct elements using custom key extractor	MoreCollectors.distinctCount()
Get the List of distinct elements using custom key extractor	MoreCollectors.distinctBy()
Simply counting, but get the result as Integer	MoreCollectors.countingInt()
Get the first or last element only	MoreCollectors.first()/last()
Get the element only if there's exactly one element	MoreCollectors.onlyOne()
Get the given number of first or last elements in the List	MoreCollectors.head()/tail()
Get the given number of greatest/least elements according to the given Comparator or natural order	MoreCollectors.greatest()/least()
Get all the maximal or minimal elements according to the given Comparator or natural order	MoreCollectors.maxAll()/minAll()
Get the index of maximal or minimal element according to the given Comparator or natural order	MoreCollectors.minIndex()/maxIndex()
Get both maximal and minimal stream element according to the given Comparator	MoreCollectors.minMax()
Get the intersection of input collections	MoreCollectors.intersecting()
Get the result bitwise-and operation	MoreCollectors.andingInt()/andingLong()
Join the elements into string with possible limit to the string length (adding ellipsis if necessary)	Joining.with()
Perform a group-by with the specified keys domain, so every key is initialized even if absent in the input	MoreCollectors.groupingBy()/groupingByEnum()
Partition input according to the Predicate	MoreCollectors.partitioningBy()
Get the common prefix or common suffix String of input elements	MoreCollectors.commonPrefix()/commonSuffix()
Get the list of input elements removing the elements which follow their dominator element	MoreCollectors.dominators()
Reduce elements possibly short-circuiting the reduction	MoreCollectors.reducingWithZero()

Adaptor collectors

What I want	How to get it
Collect using two independent collectors	MoreCollectors.pairing()
Filter the input before passing to the collector	MoreCollectors.filtering()
Map the input before passing to the collector	MoreCollectors.mapping()
Flat-map the input before passing to the collector	MoreCollectors.flatMapping()
Perform a custom final operation after the collection finishes	MoreCollectors.collectingAndThen()
Perform a downstream collection if all elements satisfy the predicate	MoreCollectors.ifAllMatch()