Class IterableUtils
Iterable instances.
 Note: This utility class has been designed with fail-fast argument checking.
- All decorator methods are not null-safe for the provided Iterable argument; for example, they will throw a NullPointerExceptionif a null Iterable is passed as argument.
- All other utility methods are null-safe for the provided Iterable argument; for example, they will treat a null Iterable the same way as an empty one.
 For other arguments which are null, a Predicatewill result in aNullPointerException. Exception: passing a nullComparatoris equivalent to a Comparator with natural ordering.
- Since:
- 4.1
- 
Constructor SummaryConstructors
- 
Method SummaryModifier and TypeMethodDescriptionstatic <E> Iterable<E> boundedIterable(Iterable<E> iterable, long maxSize) Returns a view of the given iterable that contains at most the given number of elements.static <E> Iterable<E> chainedIterable(Iterable<? extends E>... iterables) Combines the provided iterables into a single iterable.static <E> Iterable<E> chainedIterable(Iterable<? extends E> a, Iterable<? extends E> b) Combines two iterables into a single iterable.static <E> Iterable<E> chainedIterable(Iterable<? extends E> a, Iterable<? extends E> b, Iterable<? extends E> c) Combines three iterables into a single iterable.static <E> Iterable<E> chainedIterable(Iterable<? extends E> a, Iterable<? extends E> b, Iterable<? extends E> c, Iterable<? extends E> d) Combines four iterables into a single iterable.static <E> Iterable<E> collatedIterable(Iterable<? extends E> a, Iterable<? extends E> b) Combines the two provided iterables into an ordered iterable using natural ordering.static <E> Iterable<E> collatedIterable(Comparator<? super E> comparator, Iterable<? extends E> a, Iterable<? extends E> b) Combines the two provided iterables into an ordered iterable using the provided comparator.static <E> booleanChecks if the object is contained in the given iterable.static <E> booleanChecks if the object is contained in the given iterable.static <E> longcountMatches(Iterable<E> input, Predicate<? super E> predicate) Counts the number of elements in the input iterable that match the predicate.static <E> List<E> duplicateList(Iterable<E> iterable) Finds and returns the List of duplicate elements in the given collection.static <E> Set<E> duplicateSequencedSet(Iterable<E> iterable) Finds and returns the sequenced Set of duplicate elements in the given collection.static <E> Set<E> duplicateSet(Iterable<E> iterable) Finds and returns the set of duplicate elements in the given collection.static <E> Iterable<E> emptyIfNull(Iterable<E> iterable) Returns an immutable empty iterable if the argument is null, or the argument itself otherwise.static <E> Iterable<E> Gets an empty iterable.static <E> Iterable<E> filteredIterable(Iterable<E> iterable, Predicate<? super E> predicate) Returns a view of the given iterable that only contains elements matching the provided predicate.static <E> EFinds the first element in the given iterable which matches the given predicate.static <T> TShortcut forget(iterator, 0).static <E> voidApplies the closure to each element of the provided iterable.static <E> EforEachButLast(Iterable<E> iterable, Closure<? super E> closure) Executes the given closure on each but the last element in the iterable.static <E,T extends E> 
 intReturns the number of occurrences of the provided object in the iterable.static <T> TGets theindex-th value in theiterable'sIterator, throwingIndexOutOfBoundsExceptionif there is no such element.static <E> intReturns the index of the first element in the specified iterable that matches the given predicate.static booleanAnswers true if the provided iterable is empty.static <E> Iterable<E> loopingIterable(Iterable<E> iterable) Returns a view of the given iterable which will cycle infinitely over its elements.static <E> booleanmatchesAll(Iterable<E> iterable, Predicate<? super E> predicate) Answers true if a predicate is true for every element of an iterable.static <E> booleanmatchesAny(Iterable<E> iterable, Predicate<? super E> predicate) Answers true if a predicate is true for any element of the iterable.static <O,R extends Collection<O>> 
 List<R> partition(Iterable<? extends O> iterable, Factory<R> partitionFactory, Predicate<? super O>... predicates) Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicates.Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicate.Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicates.static <E> Iterable<E> reversedIterable(Iterable<E> iterable) Returns a reversed view of the given iterable.static intReturns the number of elements contained in the given iterator.static <E> Iterable<E> skippingIterable(Iterable<E> iterable, long elementsToSkip) Returns a view of the given iterable that skips the first N elements.static <E> List<E> Gets a new list with the contents of the provided iterable.static <E> StringReturns a string representation of the elements of the specified iterable.static <E> StringtoString(Iterable<E> iterable, Transformer<? super E, String> transformer) Returns a string representation of the elements of the specified iterable.static <E> StringtoString(Iterable<E> iterable, Transformer<? super E, String> transformer, String delimiter, String prefix, String suffix) Returns a string representation of the elements of the specified iterable.static <I,O> Iterable <O> transformedIterable(Iterable<I> iterable, Transformer<? super I, ? extends O> transformer) Returns a transformed view of the given iterable where all of its elements have been transformed by the provided transformer.static <E> Iterable<E> uniqueIterable(Iterable<E> iterable) Returns a unique view of the given iterable.static <E> Iterable<E> unmodifiableIterable(Iterable<E> iterable) Returns an unmodifiable view of the given iterable.static <E> Iterable<E> zippingIterable(Iterable<? extends E> a, Iterable<? extends E> b) Interleaves two iterables into a single iterable.static <E> Iterable<E> zippingIterable(Iterable<? extends E> first, Iterable<? extends E>... others) Interleaves two iterables into a single iterable.
- 
Constructor Details- 
IterableUtils
 
- 
- 
Method Details- 
boundedIterableReturns a view of the given iterable that contains at most the given number of elements.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to limit, may not be null
- maxSize- the maximum number of elements, must not be negative
- Returns:
- a bounded view on the specified iterable
- Throws:
- IllegalArgumentException- if maxSize is negative
- NullPointerException- if iterable is null
 
- 
chainedIterableCombines the provided iterables into a single iterable.The returned iterable has an iterator that traverses the elements in the order of the arguments, i.e. iterables[0], iterables[1], .... The source iterators are not polled until necessary. The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- iterables- the iterables to combine, may not be null
- Returns:
- a new iterable, combining the provided iterables
- Throws:
- NullPointerException- if either of the provided iterables is null
 
- 
chainedIterableCombines two iterables into a single iterable.The returned iterable has an iterator that traverses the elements in a, followed by the elements inb. The source iterators are not polled until necessary.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- a- the first iterable, may not be null
- b- the second iterable, may not be null
- Returns:
- a new iterable, combining the provided iterables
- Throws:
- NullPointerException- if either a or b is null
 
- 
chainedIterablepublic static <E> Iterable<E> chainedIterable(Iterable<? extends E> a, Iterable<? extends E> b, Iterable<? extends E> c) Combines three iterables into a single iterable.The returned iterable has an iterator that traverses the elements in a, followed by the elements inbandc. The source iterators are not polled until necessary.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- a- the first iterable, may not be null
- b- the second iterable, may not be null
- c- the third iterable, may not be null
- Returns:
- a new iterable, combining the provided iterables
- Throws:
- NullPointerException- if either of the provided iterables is null
 
- 
chainedIterablepublic static <E> Iterable<E> chainedIterable(Iterable<? extends E> a, Iterable<? extends E> b, Iterable<? extends E> c, Iterable<? extends E> d) Combines four iterables into a single iterable.The returned iterable has an iterator that traverses the elements in a, followed by the elements inb,candd. The source iterators are not polled until necessary.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- a- the first iterable, may not be null
- b- the second iterable, may not be null
- c- the third iterable, may not be null
- d- the fourth iterable, may not be null
- Returns:
- a new iterable, combining the provided iterables
- Throws:
- NullPointerException- if either of the provided iterables is null
 
- 
collatedIterablepublic static <E> Iterable<E> collatedIterable(Comparator<? super E> comparator, Iterable<? extends E> a, Iterable<? extends E> b) Combines the two provided iterables into an ordered iterable using the provided comparator. If the comparator is null, natural ordering will be used.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- comparator- the comparator defining an ordering over the elements, may be null, in which case natural ordering will be used
- a- the first iterable, may not be null
- b- the second iterable, may not be null
- Returns:
- a filtered view on the specified iterable
- Throws:
- NullPointerException- if either of the provided iterables is null
 
- 
collatedIterableCombines the two provided iterables into an ordered iterable using natural ordering.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- a- the first iterable, must not be null
- b- the second iterable, must not be null
- Returns:
- a filtered view on the specified iterable
- Throws:
- NullPointerException- if either of the provided iterables is null
 
- 
containspublic static <E> boolean contains(Iterable<? extends E> iterable, E object, Equator<? super E> equator) Checks if the object is contained in the given iterable. Object equality is tested with anequatorunlikecontains(Iterable, Object)which usesObject.equals(Object).A nullor empty iterable returns false. Anullobject will not be passed to the equator, instead aNullPredicatewill be used.- Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- iterable- the iterable to check, may be null
- object- the object to check
- equator- the equator to use to check, may not be null
- Returns:
- true if the object is contained in the iterable, false otherwise
- Throws:
- NullPointerException- if equator is null
 
- 
containsChecks if the object is contained in the given iterable.A nullor empty iterable returns false.- Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- iterable- the iterable to check, may be null
- object- the object to check
- Returns:
- true if the object is contained in the iterable, false otherwise
 
- 
countMatchesCounts the number of elements in the input iterable that match the predicate.A nulliterable matches no elements.- Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- input- the- Iterableto get the input from, may be null
- predicate- the predicate to use, may not be null
- Returns:
- the number of matches for the predicate in the collection
- Throws:
- NullPointerException- if predicate is null
 
- 
duplicateListFinds and returns the List of duplicate elements in the given collection.- Type Parameters:
- E- the type of elements in the collection.
- Parameters:
- iterable- the list to test, must not be null.
- Returns:
- the set of duplicate elements, may be empty.
- Since:
- 4.5.0-M3
 
- 
duplicateSequencedSetFinds and returns the sequenced Set of duplicate elements in the given collection.Once we are on Java 21 and a new major version, the return type should be SequencedSet. - Type Parameters:
- E- the type of elements in the collection.
- Parameters:
- iterable- the list to test, must not be null.
- Returns:
- the set of duplicate elements, may be empty.
- Since:
- 4.5.0-M3
 
- 
duplicateSetFinds and returns the set of duplicate elements in the given collection.- Type Parameters:
- E- the type of elements in the collection.
- Parameters:
- iterable- the list to test, must not be null.
- Returns:
- the set of duplicate elements, may be empty.
- Since:
- 4.5.0-M3
 
- 
emptyIfNullReturns an immutable empty iterable if the argument is null, or the argument itself otherwise.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable, may be null
- Returns:
- an empty iterable if the argument is null
 
- 
emptyIterableGets an empty iterable.This iterable does not contain any elements. - Type Parameters:
- E- the element type
- Returns:
- an empty iterable
 
- 
filteredIterablepublic static <E> Iterable<E> filteredIterable(Iterable<E> iterable, Predicate<? super E> predicate) Returns a view of the given iterable that only contains elements matching the provided predicate.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to filter, may not be null
- predicate- the predicate used to filter elements, may not be null
- Returns:
- a filtered view on the specified iterable
- Throws:
- NullPointerException- if either iterable or predicate is null
 
- 
findFinds the first element in the given iterable which matches the given predicate.A nullor empty iterator returns null.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to search, may be null
- predicate- the predicate to use, must not be null
- Returns:
- the first element of the iterable which matches the predicate or null if none could be found
- Throws:
- NullPointerException- if predicate is null
 
- 
firstShortcut forget(iterator, 0).Returns the firstvalue in theiterable'sIterator, throwingIndexOutOfBoundsExceptionif there is no such element.If the Iterableis aList, then it will useList.get(int).- Type Parameters:
- T- the type of object in the- Iterable.
- Parameters:
- iterable- the- Iterableto get a value from, may be null
- Returns:
- the first object
- Throws:
- IndexOutOfBoundsException- if the request is invalid
- Since:
- 4.2
 
- 
forEachApplies the closure to each element of the provided iterable.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterator to use, may be null
- closure- the closure to apply to each element, may not be null
- Throws:
- NullPointerException- if closure is null
 
- 
forEachButLastExecutes the given closure on each but the last element in the iterable.If the input iterable is null no change is made. - Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- iterable- the iterable to get the input from, may be null
- closure- the closure to perform, may not be null
- Returns:
- the last element in the iterable, or null if iterable is null or empty
 
- 
frequencyReturns the number of occurrences of the provided object in the iterable.
- 
getGets theindex-th value in theiterable'sIterator, throwingIndexOutOfBoundsExceptionif there is no such element.If the Iterableis aList, then it will useList.get(int).- Type Parameters:
- T- the type of object in the- Iterable.
- Parameters:
- iterable- the- Iterableto get a value from, may be null
- index- the index to get
- Returns:
- the object at the specified index
- Throws:
- IndexOutOfBoundsException- if the index is invalid
 
- 
indexOfReturns the index of the first element in the specified iterable that matches the given predicate.A nullor empty iterable returns -1.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to search, may be null
- predicate- the predicate to use, must not be null
- Returns:
- the index of the first element which matches the predicate or -1 if none matches
- Throws:
- NullPointerException- if predicate is null
 
- 
isEmpty
- 
loopingIterableReturns a view of the given iterable which will cycle infinitely over its elements.The returned iterable's iterator supports remove()ifiterable.iterator()does. Afterremove()is called, subsequent cycles omit the removed element, which is no longer initerable. The iterator'shasNext()method returnstrueuntiliterableis empty.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to loop, may not be null
- Returns:
- a view of the iterable, providing an infinite loop over its elements
- Throws:
- NullPointerException- if iterable is null
 
- 
matchesAllAnswers true if a predicate is true for every element of an iterable.A nullor empty iterable returns true.- Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- iterable- the- Iterableto use, may be null
- predicate- the predicate to use, may not be null
- Returns:
- true if every element of the collection matches the predicate or if the collection is empty, false otherwise
- Throws:
- NullPointerException- if predicate is null
 
- 
matchesAnyAnswers true if a predicate is true for any element of the iterable.A nullor empty iterable returns false.- Type Parameters:
- E- the type of object the- Iterablecontains
- Parameters:
- iterable- the- Iterableto use, may be null
- predicate- the predicate to use, may not be null
- Returns:
- true if any element of the collection matches the predicate, false otherwise
- Throws:
- NullPointerException- if predicate is null
 
- 
partitionpublic static <O,R extends Collection<O>> List<R> partition(Iterable<? extends O> iterable, Factory<R> partitionFactory, Predicate<? super O>... predicates) Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicates.For each predicate, the returned list will contain a collection holding all elements of the input iterable matching the predicate. The last collection contained in the list will hold all elements which didn't match any predicate: [C1, C2, R] = partition(I, P1, P2) with I = input P1 = first predicate P2 = second predicate C1 = collection of elements matching P1 C2 = collection of elements matching P2 R = collection of elements rejected by all predicates Note: elements are only added to the output collection of the first matching predicate, determined by the order of arguments. If the input iterable is null, the same is returned as for an empty iterable. If no predicates have been provided, all elements of the input collection will be added to the rejected collection.Example: for an input list [1, 2, 3, 4, 5] calling partition with predicates [x < 3] and [x < 5] will result in the following output: [[1, 2], [3, 4], [5]]. - Type Parameters:
- O- the type of object the- Iterablecontains
- R- the type of the output- Collection
- Parameters:
- iterable- the collection to get the input from, may be null
- partitionFactory- the factory used to create the output collections
- predicates- the predicates to use, may not be null
- Returns:
- a list containing the output collections
- Throws:
- NullPointerException- if any predicate is null
 
- 
partitionpublic static <O> List<List<O>> partition(Iterable<? extends O> iterable, Predicate<? super O> predicate) Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicate.For each predicate, the result will contain a list holding all elements of the input iterable matching the predicate. The last list will hold all elements which didn't match any predicate: [C1, R] = partition(I, P1) with I = input P1 = first predicate C1 = collection of elements matching P1 R = collection of elements rejected by all predicates If the input iterable is null, the same is returned as for an empty iterable.Example: for an input list [1, 2, 3, 4, 5] calling partition with a predicate [x < 3] will result in the following output: [[1, 2], [3, 4, 5]]. - Type Parameters:
- O- the type of object the- Iterablecontains
- Parameters:
- iterable- the iterable to partition, may be null
- predicate- the predicate to use, may not be null
- Returns:
- a list containing the output collections
- Throws:
- NullPointerException- if predicate is null
 
- 
partitionpublic static <O> List<List<O>> partition(Iterable<? extends O> iterable, Predicate<? super O>... predicates) Partitions all elements from iterable into separate output collections, based on the evaluation of the given predicates.For each predicate, the result will contain a list holding all elements of the input iterable matching the predicate. The last list will hold all elements which didn't match any predicate: [C1, C2, R] = partition(I, P1, P2) with I = input P1 = first predicate P2 = second predicate C1 = collection of elements matching P1 C2 = collection of elements matching P2 R = collection of elements rejected by all predicates Note: elements are only added to the output collection of the first matching predicate, determined by the order of arguments. If the input iterable is null, the same is returned as for an empty iterable.Example: for an input list [1, 2, 3, 4, 5] calling partition with predicates [x < 3] and [x < 5] will result in the following output: [[1, 2], [3, 4], [5]]. - Type Parameters:
- O- the type of object the- Iterablecontains
- Parameters:
- iterable- the collection to get the input from, may be null
- predicates- the predicates to use, may not be null
- Returns:
- a list containing the output collections
- Throws:
- NullPointerException- if any predicate is null
 
- 
reversedIterableReturns a reversed view of the given iterable.In case the provided iterable is a Listinstance, aReverseListIteratorwill be used to reverse the traversal order, otherwise an intermediateListneeds to be created.The returned iterable's iterator supports remove()if the provided iterable is aListinstance.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to use, may not be null
- Returns:
- a reversed view of the specified iterable
- Throws:
- NullPointerException- if iterable is null
- See Also:
 
- 
size
- 
skippingIterableReturns a view of the given iterable that skips the first N elements.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to use, may not be null
- elementsToSkip- the number of elements to skip from the start, must not be negative
- Returns:
- a view of the specified iterable, skipping the first N elements
- Throws:
- IllegalArgumentException- if elementsToSkip is negative
- NullPointerException- if iterable is null
 
- 
toList
- 
toStringReturns a string representation of the elements of the specified iterable.The string representation consists of a list of the iterable's elements, enclosed in square brackets ( "[]"). Adjacent elements are separated by the characters", "(a comma followed by a space). Elements are converted to strings as byString.valueOf(Object).- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to convert to a string, may be null
- Returns:
- a string representation of iterable
 
- 
toStringReturns a string representation of the elements of the specified iterable.The string representation consists of a list of the iterable's elements, enclosed in square brackets ( "[]"). Adjacent elements are separated by the characters", "(a comma followed by a space). Elements are converted to strings as by using the providedtransformer.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to convert to a string, may be null
- transformer- the transformer used to get a string representation of an element
- Returns:
- a string representation of iterable
- Throws:
- NullPointerException- if- transformeris null
 
- 
toStringpublic static <E> String toString(Iterable<E> iterable, Transformer<? super E, String> transformer, String delimiter, String prefix, String suffix) Returns a string representation of the elements of the specified iterable.The string representation consists of a list of the iterable's elements, enclosed by the provided prefixandsuffix. Adjacent elements are separated by the provideddelimiter. Elements are converted to strings as by using the providedtransformer.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to convert to a string, may be null
- transformer- the transformer used to get a string representation of an element
- delimiter- the string to delimit elements
- prefix- the prefix, prepended to the string representation
- suffix- the suffix, appended to the string representation
- Returns:
- a string representation of iterable
- Throws:
- NullPointerException- if either transformer, delimiter, prefix or suffix is null
 
- 
transformedIterablepublic static <I,O> Iterable<O> transformedIterable(Iterable<I> iterable, Transformer<? super I, ? extends O> transformer) Returns a transformed view of the given iterable where all of its elements have been transformed by the provided transformer.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- I- the input element type
- O- the output element type
- Parameters:
- iterable- the iterable to transform, may not be null
- transformer- the transformer, must not be null
- Returns:
- a transformed view of the specified iterable
- Throws:
- NullPointerException- if either iterable or transformer is null
 
- 
uniqueIterableReturns a unique view of the given iterable.The returned iterable's iterator supports remove()when the corresponding input iterator supports it. Callingremove()will only remove a single element from the underlying iterator.- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to use, may not be null
- Returns:
- a unique view of the specified iterable
- Throws:
- NullPointerException- if iterable is null
 
- 
unmodifiableIterableReturns an unmodifiable view of the given iterable.The returned iterable's iterator does not support remove().- Type Parameters:
- E- the element type
- Parameters:
- iterable- the iterable to use, may not be null
- Returns:
- an unmodifiable view of the specified iterable
- Throws:
- NullPointerException- if iterable is null
 
- 
zippingIterableInterleaves two iterables into a single iterable.The returned iterable has an iterator that traverses the elements in aandbin alternating order. The source iterators are not polled until necessary.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- a- the first iterable, may not be null
- b- the second iterable, may not be null
- Returns:
- a new iterable, interleaving the provided iterables
- Throws:
- NullPointerException- if either a or b is null
 
- 
zippingIterablepublic static <E> Iterable<E> zippingIterable(Iterable<? extends E> first, Iterable<? extends E>... others) Interleaves two iterables into a single iterable.The returned iterable has an iterator that traverses the elements in aandbin alternating order. The source iterators are not polled until necessary.The returned iterable's iterator supports remove()when the corresponding input iterator supports it.- Type Parameters:
- E- the element type
- Parameters:
- first- the first iterable, may not be null
- others- the array of iterables to interleave, may not be null
- Returns:
- a new iterable, interleaving the provided iterables
- Throws:
- NullPointerException- if either of the provided iterables is null
 
 
-