FluentIterable (Guava: Google Core Libraries for Java 19.0 API)

java.lang.Object
- com.google.common.collect.FluentIterable<E>

All Implemented Interfaces:

Iterable<E>
```
@GwtCompatible(emulated=true)
public abstract class FluentIterable<E>
extends Object
implements Iterable<E>
```
An expanded Iterable API, providing functionality similar to Java 8's powerful streams library in a slightly different way.
The following types of methods are provided:
- chaining methods which return a new FluentIterable based in some way on the contents of the current one (for example transform(com.google.common.base.Function<? super E, T>))
- element extraction methods which facilitate the retrieval of certain elements (for example last())
- query methods which answer questions about the FluentIterable's contents (for example anyMatch(com.google.common.base.Predicate<? super E>))
- conversion methods which copy the FluentIterable's contents into a new collection or array (for example toList())
Several lesser-used features are currently available only as static methods on the Iterables class.
Comparison to streams

Starting with Java 8, the core Java class libraries provide a new "Streams" library (in java.util.stream), which is similar to FluentIterable but generally more powerful. Key differences include:
- A stream is single-use; it becomes invalid as soon as any "terminal operation" such as findFirst() or iterator() is invoked. (Even though Stream contains all the right method signatures to implement Iterable, it does not actually do so, to avoid implying repeat-iterability.) FluentIterable, on the other hand, is multiple-use, and does implement Iterable.
- Streams offer many features not found here, including min/max, distinct, reduce, sorted, the very powerful collect, and built-in support for parallelizing stream operations.
- FluentIterable contains several features not available on Stream, which are noted in the method descriptions below.
- Streams include primitive-specialized variants such as IntStream, the use of which is strongly recommended.
- Streams are standard Java, not requiring a third-party dependency (but do render your code incompatible with Java 7 and earlier).
Example

Here is an example that accepts a list from a database call, filters it based on a predicate, transforms it by invoking toString() on each element, and returns the first 10 elements as a List:
```
   List<String> results =
       FluentIterable.from(database.getClientList())
           .filter(activeInLastMonthPredicate)
           .transform(Functions.toStringFunction())
           .limit(10)
           .toList();
```
The approximate stream equivalent is:
```
   List<String> results =
       database.getClientList()
           .stream()
           .filter(activeInLastMonthPredicate)
           .map(Functions.toStringFunction())
           .limit(10)
           .collect(Collectors.toList());
```
Since:

12.0

Author:

Marcin Mikosik

Constructor Summary

Constructors
Modifier Constructor and Description

protected FluentIterable()
Constructor for use by subclasses.

Constructors
Modifier	Constructor and Description
`protected`	`FluentIterable()` Constructor for use by subclasses.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`allMatch(Predicate<? super E> predicate)` Returns `true` if every element in this fluent iterable satisfies the predicate.
`boolean`	`anyMatch(Predicate<? super E> predicate)` Returns `true` if any element in this fluent iterable satisfies the predicate.
`FluentIterable<E>`	`append(E... elements)` Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, followed by `elements`.
`FluentIterable<E>`	`append(Iterable<? extends E> other)` Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, followed by those of `other`.
`boolean`	`contains(Object target)` Returns `true` if this fluent iterable contains any object for which `equals(target)` is true.
`<C extends Collection<? super E>> C`	`copyInto(C collection)` Copies all the elements from this fluent iterable to `collection`.
`FluentIterable<E>`	`cycle()` Returns a fluent iterable whose `Iterator` cycles indefinitely over the elements of this fluent iterable.
`<T> FluentIterable<T>`	`filter(Class<T> type)` Returns the elements from this fluent iterable that are instances of class `type`.
`FluentIterable<E>`	`filter(Predicate<? super E> predicate)` Returns the elements from this fluent iterable that satisfy a predicate.
`Optional<E>`	`first()` Returns an `Optional` containing the first element in this fluent iterable.
`Optional<E>`	`firstMatch(Predicate<? super E> predicate)` Returns an `Optional` containing the first element in this fluent iterable that satisfies the given predicate, if such an element exists.
`static <E> FluentIterable<E>`	`from(FluentIterable<E> iterable)` Deprecated. instances of `FluentIterable` don't need to be converted to `FluentIterable`
`static <E> FluentIterable<E>`	`from(Iterable<E> iterable)` Returns a fluent iterable that wraps `iterable`, or `iterable` itself if it is already a `FluentIterable`.
`E`	`get(int position)` Returns the element at the specified position in this fluent iterable.
`<K> ImmutableListMultimap<K,E>`	`index(Function<? super E,K> keyFunction)` Creates an index `ImmutableListMultimap` that contains the results of applying a specified function to each item in this `FluentIterable` of values.
`boolean`	`isEmpty()` Determines whether this fluent iterable is empty.
`String`	`join(Joiner joiner)` Returns a `String` containing all of the elements of this fluent iterable joined with `joiner`.
`Optional<E>`	`last()` Returns an `Optional` containing the last element in this fluent iterable.
`FluentIterable<E>`	`limit(int maxSize)` Creates a fluent iterable with the first `size` elements of this fluent iterable.
`static <E> FluentIterable<E>`	`of(E[] elements)` Returns a fluent iterable containing `elements` in the specified order.
`int`	`size()` Returns the number of elements in this fluent iterable.
`FluentIterable<E>`	`skip(int numberToSkip)` Returns a view of this fluent iterable that skips its first `numberToSkip` elements.
`E[]`	`toArray(Class<E> type)` Returns an array containing all of the elements from this fluent iterable in iteration order.
`ImmutableList<E>`	`toList()` Returns an `ImmutableList` containing all of the elements from this fluent iterable in proper sequence.
`<V> ImmutableMap<E,V>`	`toMap(Function<? super E,V> valueFunction)` Returns an immutable map whose keys are the distinct elements of this `FluentIterable` and whose value for each key was computed by `valueFunction`.
`ImmutableMultiset<E>`	`toMultiset()` Returns an `ImmutableMultiset` containing all of the elements from this fluent iterable.
`ImmutableSet<E>`	`toSet()` Returns an `ImmutableSet` containing all of the elements from this fluent iterable with duplicates removed.
`ImmutableList<E>`	`toSortedList(Comparator<? super E> comparator)` Returns an `ImmutableList` containing all of the elements from this `FluentIterable` in the order specified by `comparator`.
`ImmutableSortedSet<E>`	`toSortedSet(Comparator<? super E> comparator)` Returns an `ImmutableSortedSet` containing all of the elements from this `FluentIterable` in the order specified by `comparator`, with duplicates (determined by `comparator.compare(x, y) == 0`) removed.
`String`	`toString()` Returns a string representation of this fluent iterable, with the format `[e1, e2, ..., en]`.
`<T> FluentIterable<T>`	`transform(Function<? super E,T> function)` Returns a fluent iterable that applies `function` to each element of this fluent iterable.
`<T> FluentIterable<T>`	`transformAndConcat(Function<? super E,? extends Iterable<? extends T>> function)` Applies `function` to each element of this fluent iterable and returns a fluent iterable with the concatenated combination of results.
`<K> ImmutableMap<K,E>`	`uniqueIndex(Function<? super E,K> keyFunction)` Returns a map with the contents of this `FluentIterable` as its `values`, indexed by keys derived from those values.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.lang.Iterable
iterator

- Constructor Detail
  - FluentIterable
```
protected FluentIterable()
```
    Constructor for use by subclasses.
- Method Detail
  - from
```
@CheckReturnValue
public static <E> FluentIterable<E> from(Iterable<E> iterable)
```
    Returns a fluent iterable that wraps iterable, or iterable itself if it is already a FluentIterable.
    Stream equivalent: iterable.stream() if iterable is a Collection; StreamSupport.stream(iterable.spliterator(), false) otherwise.
  - from
```
@Deprecated
@CheckReturnValue
public static <E> FluentIterable<E> from(FluentIterable<E> iterable)
```
    Deprecated. instances of FluentIterable don't need to be converted to FluentIterable
    
    Construct a fluent iterable from another fluent iterable. This is obviously never necessary, but is intended to help call out cases where one migration from Iterable to FluentIterable has obviated the need to explicitly convert to a FluentIterable.
  - of
```
@Beta
@CheckReturnValue
public static <E> FluentIterable<E> of(E[] elements)
```
    Returns a fluent iterable containing elements in the specified order.
    Stream equivalent: Stream.of(elements) or Arrays.stream(elements).
    
    Since:
    
    18.0
  - toString
```
@CheckReturnValue
public String toString()
```
    Returns a string representation of this fluent iterable, with the format [e1, e2, ..., en].
    Stream equivalent: stream.collect(Collectors.joining(", ", "[", "]")) or (less efficiently) collect(Collectors.toList()).toString().
    
    Overrides:
    
    toString in class Object
  - size
```
@CheckReturnValue
public final int size()
```
    Returns the number of elements in this fluent iterable.
    Stream equivalent: stream.count().
  - contains
```
@CheckReturnValue
public final boolean contains(@Nullable
                                Object target)
```
    Returns true if this fluent iterable contains any object for which equals(target) is true.
    Stream equivalent: stream.anyMatch(Predicate.isEqual(target)).
  - cycle
```
@CheckReturnValue
public final FluentIterable<E> cycle()
```
    Returns a fluent iterable whose Iterator cycles indefinitely over the elements of this fluent iterable.
    That iterator supports remove() if iterable.iterator() does. After remove() is called, subsequent cycles omit the removed element, which is no longer in this fluent iterable. The iterator's hasNext() method returns true until this fluent iterable is empty.
    Warning: Typical uses of the resulting iterator may produce an infinite loop. You should use an explicit break or be certain that you will eventually remove all the elements.
    Stream equivalent: if the source iterable has only a single element element, use Stream.generate(() -> element). Otherwise, if the source iterable has a stream method (for example, if it is a Collection), use Stream.generate(iterable::stream).flatMap(s -> s).
  - append
```
@Beta
@CheckReturnValue
public final FluentIterable<E> append(Iterable<? extends E> other)
```
    Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, followed by those of other. The iterators are not polled until necessary.
    The returned iterable's Iterator supports remove() when the corresponding Iterator supports it.
    Stream equivalent: Stream.concat(thisStream, otherStream).
    
    Since:
    
    18.0
  - append
```
@Beta
@CheckReturnValue
public final FluentIterable<E> append(E... elements)
```
    Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable, followed by elements.
    Stream equivalent: Stream.concat(thisStream, Stream.of(elements)).
    
    Since:
    
    18.0
  - filter
```
@CheckReturnValue
public final FluentIterable<E> filter(Predicate<? super E> predicate)
```
    Returns the elements from this fluent iterable that satisfy a predicate. The resulting fluent iterable's iterator does not support remove().
    Stream equivalent: stream.filter(predicate) (same).
  - filter
```
@GwtIncompatible(value="Class.isInstance")
@CheckReturnValue
public final <T> FluentIterable<T> filter(Class<T> type)
```
    Returns the elements from this fluent iterable that are instances of class type.
    Parameters:
    type - the type of elements desired
    Stream equivalent:
    {@code
  - anyMatch
```
@CheckReturnValue
public final boolean anyMatch(Predicate<? super E> predicate)
```
    Returns true if any element in this fluent iterable satisfies the predicate.
    Stream equivalent: stream.anyMatch(predicate) (same).
  - allMatch
```
@CheckReturnValue
public final boolean allMatch(Predicate<? super E> predicate)
```
    Returns true if every element in this fluent iterable satisfies the predicate. If this fluent iterable is empty, true is returned.
    Stream equivalent: stream.allMatch(predicate) (same).
  - firstMatch
```
@CheckReturnValue
public final Optional<E> firstMatch(Predicate<? super E> predicate)
```
    Returns an Optional containing the first element in this fluent iterable that satisfies the given predicate, if such an element exists.
    Warning: avoid using a predicate that matches null. If null is matched in this fluent iterable, a NullPointerException will be thrown.
    Stream equivalent: stream.filter(predicate).findFirst().
  - transform
```
@CheckReturnValue
public final <T> FluentIterable<T> transform(Function<? super E,T> function)
```
    Returns a fluent iterable that applies function to each element of this fluent iterable.
    The returned fluent iterable's iterator supports remove() if this iterable's iterator does. After a successful remove() call, this fluent iterable no longer contains the corresponding element.
    Stream equivalent: stream.map(function).
  - transformAndConcat
```
@CheckReturnValue
public <T> FluentIterable<T> transformAndConcat(Function<? super E,? extends Iterable<? extends T>> function)
```
    Applies function to each element of this fluent iterable and returns a fluent iterable with the concatenated combination of results. function returns an Iterable of results.
    The returned fluent iterable's iterator supports remove() if this function-returned iterables' iterator does. After a successful remove() call, the returned fluent iterable no longer contains the corresponding element.
    Stream equivalent: stream.flatMap(function) (using a function that produces streams, not iterables).
    
    Since:
    
    13.0 (required Function<E, Iterable<T>> until 14.0)
  - first
```
@CheckReturnValue
public final Optional<E> first()
```
    Returns an Optional containing the first element in this fluent iterable. If the iterable is empty, Optional.absent() is returned.
    Stream equivalent: if the goal is to obtain any element, stream.findAny(); if it must specifically be the first element, stream.findFirst().
    
    Throws:
    
    NullPointerException - if the first element is null; if this is a possibility, use iterator().next() or Iterables.getFirst(java.lang.Iterable<? extends T>, T) instead.
  - last
```
@CheckReturnValue
public final Optional<E> last()
```
    Returns an Optional containing the last element in this fluent iterable. If the iterable is empty, Optional.absent() is returned.
    Stream equivalent: stream.reduce((a, b) -> b).
    
    Throws:
    
    NullPointerException - if the last element is null; if this is a possibility, use Iterables.getLast(java.lang.Iterable<T>) instead.
  - skip
```
@CheckReturnValue
public final FluentIterable<E> skip(int numberToSkip)
```
    Returns a view of this fluent iterable that skips its first numberToSkip elements. If this fluent iterable contains fewer than numberToSkip elements, the returned fluent iterable skips all of its elements.
    Modifications to this fluent iterable before a call to iterator() are reflected in the returned fluent iterable. That is, the its iterator skips the first numberToSkip elements that exist when the iterator is created, not when skip() is called.
    The returned fluent iterable's iterator supports remove() if the Iterator of this fluent iterable supports it. Note that it is not possible to delete the last skipped element by immediately calling remove() on the returned fluent iterable's iterator, as the Iterator contract states that a call to * remove() before a call to next() will throw an IllegalStateException.
    Stream equivalent: stream.skip(numberToSkip) (same).
  - limit
```
@CheckReturnValue
public final FluentIterable<E> limit(int maxSize)
```
    Creates a fluent iterable with the first size elements of this fluent iterable. If this fluent iterable does not contain that many elements, the returned fluent iterable will have the same behavior as this fluent iterable. The returned fluent iterable's iterator supports remove() if this fluent iterable's iterator does.
    Stream equivalent: stream.limit(maxSize) (same).
    
    Parameters:
    maxSize - the maximum number of elements in the returned fluent iterable
    
    Throws:
    
    IllegalArgumentException - if size is negative
  - isEmpty
```
@CheckReturnValue
public final boolean isEmpty()
```
    Determines whether this fluent iterable is empty.
    Stream equivalent: !stream.findAny().isPresent().
  - toList
```
@CheckReturnValue
public final ImmutableList<E> toList()
```
    Returns an ImmutableList containing all of the elements from this fluent iterable in proper sequence.
    Stream equivalent: ImmutableList.copyOf(stream.iterator()).
    
    Since:
    
    14.0 (since 12.0 as toImmutableList()).
  - toSortedList
```
@CheckReturnValue
public final ImmutableList<E> toSortedList(Comparator<? super E> comparator)
```
    Returns an ImmutableList containing all of the elements from this FluentIterable in the order specified by comparator. To produce an ImmutableList sorted by its natural ordering, use toSortedList(Ordering.natural()).
    Stream equivalent: ImmutableList.copyOf(stream.sorted(comparator).iterator()).
    
    Parameters:
    comparator - the function by which to sort list elements
    
    Throws:
    
    NullPointerException - if any element is null
    Since:
    
    14.0 (since 13.0 as toSortedImmutableList()).
  - toSet
```
@CheckReturnValue
public final ImmutableSet<E> toSet()
```
    Returns an ImmutableSet containing all of the elements from this fluent iterable with duplicates removed.
    Stream equivalent: ImmutableSet.copyOf(stream.iterator()).
    
    Since:
    
    14.0 (since 12.0 as toImmutableSet()).
  - toSortedSet
```
@CheckReturnValue
public final ImmutableSortedSet<E> toSortedSet(Comparator<? super E> comparator)
```
    Returns an ImmutableSortedSet containing all of the elements from this FluentIterable in the order specified by comparator, with duplicates (determined by comparator.compare(x, y) == 0) removed. To produce an ImmutableSortedSet sorted by its natural ordering, use toSortedSet(Ordering.natural()).
    Stream equivalent: ImmutableSortedSet.copyOf(comparator, stream.iterator()).
    
    Parameters:
    comparator - the function by which to sort set elements
    
    Throws:
    
    NullPointerException - if any element is null
    Since:
    
    14.0 (since 12.0 as toImmutableSortedSet()).
  - toMultiset
```
@CheckReturnValue
public final ImmutableMultiset<E> toMultiset()
```
    Returns an ImmutableMultiset containing all of the elements from this fluent iterable.
    Stream equivalent: ImmutableMultiset.copyOf(stream.iterator()).
    
    Since:
    
    19.0
  - toMap
```
@CheckReturnValue
public final <V> ImmutableMap<E,V> toMap(Function<? super E,V> valueFunction)
```
    Returns an immutable map whose keys are the distinct elements of this FluentIterable and whose value for each key was computed by valueFunction. The map's iteration order is the order of the first appearance of each key in this iterable.
    When there are multiple instances of a key in this iterable, it is unspecified whether valueFunction will be applied to more than one instance of that key and, if it is, which result will be mapped to that key in the returned map.
    Stream equivalent: ImmutableMap.copyOf(stream.collect(Collectors.toMap(k -> k, valueFunction))) (but note that this may not preserve the order of entries).
    
    Throws:
    
    NullPointerException - if any element of this iterable is null, or if valueFunction produces null for any key
    Since:
    
    14.0
  - index
```
@CheckReturnValue
public final <K> ImmutableListMultimap<K,E> index(Function<? super E,K> keyFunction)
```
    Creates an index ImmutableListMultimap that contains the results of applying a specified function to each item in this FluentIterable of values. Each element of this iterable will be stored as a value in the resulting multimap, yielding a multimap with the same size as this iterable. The key used to store that value in the multimap will be the result of calling the function on that value. The resulting multimap is created as an immutable snapshot. In the returned multimap, keys appear in the order they are first encountered, and the values corresponding to each key appear in the same order as they are encountered.
    Parameters:
    keyFunction - the function used to produce the key for each value
    
    Throws:
    NullPointerException - if any of the following cases is true:
    
    keyFunction is null
    An element in this fluent iterable is null
    keyFunction returns null for any element of this iterable
    
    Stream equivalent: stream.collect(Collectors.groupingBy(keyFunction)) behaves similarly, but returns a mutable Map<K, List<E>> instead, and may not preserve the order of entries).
    Since:
    
    14.0
  - uniqueIndex
```
@CheckReturnValue
public final <K> ImmutableMap<K,E> uniqueIndex(Function<? super E,K> keyFunction)
```
    Returns a map with the contents of this FluentIterable as its values, indexed by keys derived from those values. In other words, each input value produces an entry in the map whose key is the result of applying keyFunction to that value. These entries appear in the same order as they appeared in this fluent iterable. Example usage:
```
   Color red = new Color("red", 255, 0, 0);
   ...
   FluentIterable<Color> allColors = FluentIterable.from(ImmutableSet.of(red, green, blue));

   Map<String, Color> colorForName = allColors.uniqueIndex(toStringFunction());
   assertThat(colorForName).containsEntry("red", red);
```
    If your index may associate multiple values with each key, use index.
    Stream equivalent: ImmutableMap.copyOf(stream.collect(Collectors.toMap(keyFunction, v -> v))) (but note that this may not preserve the order of entries).
    Parameters:
    keyFunction - the function used to produce the key for each value
    
    Returns:
    a map mapping the result of evaluating the function keyFunction on each value in this fluent iterable to that value
    
    Throws:
    
    IllegalArgumentException - if keyFunction produces the same key for more than one value in this fluent iterable
    
    NullPointerException - if any elements of this fluent iterable is null, or if keyFunction produces null for any value
    Since:
    
    14.0
  - toArray
```
@GwtIncompatible(value="Array.newArray(Class, int)")
@CheckReturnValue
public final E[] toArray(Class<E> type)
```
    Returns an array containing all of the elements from this fluent iterable in iteration order.
    Stream equivalent: if an object array is acceptable, use stream.toArray(); if type is a class literal such as MyType.class, use stream.toArray(MyType[]::new). Otherwise use stream.toArray( len -> (E[]) Array.newInstance(type, len)).
    
    Parameters:
    type - the type of the elements
    
    Returns:
    a newly-allocated array into which all the elements of this fluent iterable have been copied
  - copyInto
```
public final <C extends Collection<? super E>> C copyInto(C collection)
```
    Copies all the elements from this fluent iterable to collection. This is equivalent to calling Iterables.addAll(collection, this).
    Stream equivalent: stream.forEachOrdered(collection::add) or stream.forEach(collection::add).
    
    Parameters:
    collection - the collection to copy elements to
    
    Returns:
    collection, for convenience
    Since:
    
    14.0
  - join
```
@Beta
@CheckReturnValue
public final String join(Joiner joiner)
```
    Returns a String containing all of the elements of this fluent iterable joined with joiner.
    Stream equivalent: joiner.join(stream.iterator()), or, if you are not using any optional Joiner features, stream.collect(Collectors.joining(delimiter).
    
    Since:
    
    18.0
  - get
```
@CheckReturnValue
public final E get(int position)
```
    Returns the element at the specified position in this fluent iterable.
    Stream equivalent: stream.skip(position).findFirst().get() (but note that this throws different exception types, and throws an exception if null would be returned).
    
    Parameters:
    position - position of the element to return
    
    Returns:
    the element at the specified position in this fluent iterable
    
    Throws:
    
    IndexOutOfBoundsException - if position is negative or greater than or equal to the size of this fluent iterable

Class FluentIterable<E>

Comparison to streams

Example

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.lang.Iterable

Constructor Detail

FluentIterable

Method Detail

from

from

of

toString

size

contains

cycle

append

append

filter

filter

anyMatch

allMatch

firstMatch

transform

transformAndConcat

first

last

skip

limit

isEmpty

toList

toSortedList

toSet

toSortedSet

toMultiset

toMap

index

uniqueIndex

toArray

copyInto

join

get