Package org.apache.commons.collections4

Class IterableUtils

java.lang.Object

org.apache.commons.collections4.IterableUtils

public class IterableUtils
extends Object

Provides utility methods and decorators for 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 NullPointerException if 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 Predicate will result in a NullPointerException. Exception: passing a null Comparator is equivalent to a Comparator with natural ordering.

Since:

4.1

Constructor Summary

Constructors

Constructor	Description
IterableUtils()	Deprecated. TODO Make private in 5.0.

Method Summary

Modifier and Type	Method	Description
static <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> boolean	contains(Iterable<? extends E> iterable, E object, Equator<? super E> equator)	Checks if the object is contained in the given iterable.
static <E> boolean	contains(Iterable<E> iterable, Object object)	Checks if the object is contained in the given iterable.
static <E> long	countMatches(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>	emptyIterable()	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> E	find(Iterable<E> iterable, Predicate<? super E> predicate)	Finds the first element in the given iterable which matches the given predicate.
static <T> T	first(Iterable<T> iterable)	Shortcut for get(iterator, 0).
static <E> void	forEach(Iterable<E> iterable, Closure<? super E> closure)	Applies the closure to each element of the provided iterable.
static <E> E	forEachButLast(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> int	frequency(Iterable<E> iterable, T obj)	Returns the number of occurrences of the provided object in the iterable.
static <T> T	get(Iterable<T> iterable, int index)	Gets the index-th value in the iterable's Iterator, throwing IndexOutOfBoundsException if there is no such element.
static <E> int	indexOf(Iterable<E> iterable, Predicate<? super E> predicate)	Returns the index of the first element in the specified iterable that matches the given predicate.
static boolean	isEmpty(Iterable<?> iterable)	Answers 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> boolean	matchesAll(Iterable<E> iterable, Predicate<? super E> predicate)	Answers true if a predicate is true for every element of an iterable.
static <E> boolean	matchesAny(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.
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.
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.
static <E> Iterable<E>	reversedIterable(Iterable<E> iterable)	Returns a reversed view of the given iterable.
static int	size(Iterable<?> iterable)	Returns 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> int	sumSizesToInt(Iterable<? extends Collection<E>> iterable)	Returns the sum of the sizes of the collections in the given iterable.
static <E> List<E>	toList(Iterable<E> iterable)	Gets a new list with the contents of the provided iterable.
static <E> String	toString(Iterable<E> iterable)	Returns a string representation of the elements of the specified iterable.
static <E> String	toString(Iterable<E> iterable, Transformer<? super E,String> transformer)	Returns a string representation of the elements of the specified iterable.
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.
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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

IterableUtils

@Deprecated
public IterableUtils()

Deprecated.

TODO Make private in 5.0.

Make private in 5.0.

Method Details

boundedIterable

public static <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.

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.

chainedIterable

public static <E> Iterable<E> chainedIterable(Iterable<? extends E>... iterables)

Combines 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.

chainedIterable

public static <E> Iterable<E> chainedIterable(Iterable<? extends E> a,
 Iterable<? extends E> b)

Combines two iterables into a single iterable.

The returned iterable has an iterator that traverses the elements in a, followed by the elements in b. 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.

chainedIterable

public 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 in b and c. 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.

chainedIterable

public 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 in b, c and d. 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.

collatedIterable

public 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.

collatedIterable

public 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.

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.

contains

public 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 an equator unlike contains(Iterable, Object) which uses Object.equals(Object).

A null or empty iterable returns false. A null object will not be passed to the equator, instead a NullPredicate will be used.

Type Parameters:

E - The type of object the Iterable contains.

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.

contains

public static <E> boolean contains(Iterable<E> iterable,
 Object object)

Checks if the object is contained in the given iterable.

A null or empty iterable returns false.

Type Parameters:

E - The type of object the Iterable contains.

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.

countMatches

public static <E> long countMatches(Iterable<E> input,
 Predicate<? super E> predicate)

Counts the number of elements in the input iterable that match the predicate.

A null iterable matches no elements.

Type Parameters:

E - The type of object the Iterable contains.

Parameters:

input - The Iterable to 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.

duplicateList

public static <E> List<E> duplicateList(Iterable<E> iterable)

Finds 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.

Throws:

NullPointerException - if iterable is null.

Since:

4.5.0-M3

duplicateSequencedSet

public static <E> Set<E> duplicateSequencedSet(Iterable<E> iterable)

Finds 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.

Throws:

NullPointerException - if iterable is null.

Since:

4.5.0-M3

duplicateSet

public static <E> Set<E> duplicateSet(Iterable<E> iterable)

Finds 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.

Throws:

NullPointerException - if iterable is null.

Since:

4.5.0-M3

emptyIfNull

public static <E> Iterable<E> emptyIfNull(Iterable<E> iterable)

Returns 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.

emptyIterable

public static <E> Iterable<E> emptyIterable()

Gets an empty iterable.

This iterable does not contain any elements.

Type Parameters:

E - The element type.

Returns:

An empty iterable.

filteredIterable

public 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.

find

public static <E> E find(Iterable<E> iterable,
 Predicate<? super E> predicate)

Finds the first element in the given iterable which matches the given predicate.

A null or 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.

first

public static <T> T first(Iterable<T> iterable)

Shortcut for get(iterator, 0).

Returns the first value in the iterable's Iterator, throwing IndexOutOfBoundsException if there is no such element.

If the Iterable is a List, then it will use List.get(int).

Type Parameters:

T - The type of object in the Iterable.

Parameters:

iterable - The Iterable to get a value from, may be null.

Returns:

The first object.

Throws:

IndexOutOfBoundsException - if the request is invalid.

Since:

4.2

forEach

public static <E> void forEach(Iterable<E> iterable,
 Closure<? super E> closure)

Applies 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.

forEachButLast

public static <E> E forEachButLast(Iterable<E> iterable,
 Closure<? super E> closure)

Executes 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 Iterable contains.

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.

frequency

public static <E,
T extends E> int frequency(Iterable<E> iterable,
 T obj)

Returns the number of occurrences of the provided object in the iterable.

Type Parameters:

E - The element type that the Iterable may contain.

T - The element type of the object to find.

Parameters:

iterable - The Iterable to search.

obj - The object to find the cardinality of.

Returns:

The number of occurrences of obj in iterable.

get

public static <T> T get(Iterable<T> iterable,
 int index)

Gets the index-th value in the iterable's Iterator, throwing IndexOutOfBoundsException if there is no such element.

If the Iterable is a List, then it will use List.get(int).

Type Parameters:

T - The type of object in the Iterable.

Parameters:

iterable - The Iterable to 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.

indexOf

public static <E> int indexOf(Iterable<E> iterable,
 Predicate<? super E> predicate)

Returns the index of the first element in the specified iterable that matches the given predicate.

A null or 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

public static boolean isEmpty(Iterable<?> iterable)

Answers true if the provided iterable is empty.

A null iterable returns true.

Parameters:

iterable - The to use, may be null.

Returns:

true if the iterable is null or empty, false otherwise.

loopingIterable

public static <E> Iterable<E> loopingIterable(Iterable<E> iterable)

Returns a view of the given iterable which will cycle infinitely over its elements.

The returned iterable's iterator supports remove() if iterable.iterator() does. After remove() is called, subsequent cycles omit the removed element, which is no longer in iterable. The iterator's hasNext() method returns true until iterable is 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.

matchesAll

public static <E> boolean matchesAll(Iterable<E> iterable,
 Predicate<? super E> predicate)

Answers true if a predicate is true for every element of an iterable.

A null or empty iterable returns true.

Type Parameters:

E - The type of object the Iterable contains.

Parameters:

iterable - The Iterable to 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.

matchesAny

public static <E> boolean matchesAny(Iterable<E> iterable,
 Predicate<? super E> predicate)

Answers true if a predicate is true for any element of the iterable.

A null or empty iterable returns false.

Type Parameters:

E - The type of object the Iterable contains.

Parameters:

iterable - The Iterable to 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.

partition

public 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 Iterable contains.

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.

partition

public 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 Iterable contains.

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.

partition

public 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 Iterable contains.

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.

reversedIterable

public static <E> Iterable<E> reversedIterable(Iterable<E> iterable)

Returns a reversed view of the given iterable.

In case the provided iterable is a List instance, a ReverseListIterator will be used to reverse the traversal order, otherwise an intermediate List needs to be created.

The returned iterable's iterator supports remove() if the provided iterable is a List instance.

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:

• ReverseListIterator

size

public static int size(Iterable<?> iterable)

Returns the number of elements contained in the given iterator.

A null or empty iterator returns 0.

Parameters:

iterable - The iterable to check, may be null

Returns:

The number of elements contained in the iterable

skippingIterable

public static <E> Iterable<E> skippingIterable(Iterable<E> iterable,
 long elementsToSkip)

Returns 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.

sumSizesToInt

public static <E> int sumSizesToInt(Iterable<? extends Collection<E>> iterable)

Returns the sum of the sizes of the collections in the given iterable.

Integer overflow is capped at Integer.MAX_VALUE.

Type Parameters:

E - The element type of the collections in the iterable.

Parameters:

iterable - The iterable of collections to sum the sizes of, must not be null.

Returns:

The sum of the sizes of the collections in the iterable, capped at Integer.MAX_VALUE.

Throws:

NullPointerException - if iterable is null.

Since:

4.6.0

toList

public static <E> List<E> toList(Iterable<E> iterable)

Gets a new list with the contents of the provided iterable.

Type Parameters:

E - The element type.

Parameters:

iterable - The iterable to use, may be null.

Returns:

A list of the iterator contents.

toString

public static <E> String toString(Iterable<E> iterable)

Returns 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 String.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.

toString

public static <E> String toString(Iterable<E> iterable,
 Transformer<? super E,String> transformer)

Returns 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 provided transformer.

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 transformer is null

toString

public 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 prefix and suffix. Adjacent elements are separated by the provided delimiter. Elements are converted to strings as by using the provided transformer.

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.

transformedIterable

public 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.

uniqueIterable

public static <E> Iterable<E> uniqueIterable(Iterable<E> iterable)

Returns a unique view of the given iterable.

The returned iterable's iterator supports remove() when the corresponding input iterator supports it. Calling remove() 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.

unmodifiableIterable

public static <E> Iterable<E> unmodifiableIterable(Iterable<E> iterable)

Returns 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.

zippingIterable

public static <E> Iterable<E> zippingIterable(Iterable<? extends E> a,
 Iterable<? extends E> b)

Interleaves two iterables into a single iterable.

The returned iterable has an iterator that traverses the elements in a and b in 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.

zippingIterable

public 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 a and b in 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.