com.google.common.collect
Class FluentIterable<E>

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

All Implemented Interfaces:

Iterable<E>

@Beta
@GwtCompatible(emulated=true)
public abstract class FluentIterable<E>
extends Object
implements Iterable<E>

FluentIterable provides a rich interface for manipulating Iterables in a chained fashion. A FluentIterable can be created from an Iterable, or from a set of elements. The following types of methods are provided on FluentIterable:

• chained 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))
• conversion methods which copy the FluentIterable's contents into a new collection or array (for example toImmutableList())
• 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))

Here is an example that merges the lists returned by two separate database calls, transforms it by invoking toString() on each element, and returns the first 10 elements as an ImmutableList:

   FluentIterable
       .from(database.getClientList())
       .filter(activeInLastMonth())
       .transform(Functions.toStringFunction())
       .limit(10)
       .toImmutableList();

Anything which can be done using FluentIterable could be done in a different fashion (often with Iterables), however the use of FluentIterable makes many sets of operations significantly more concise.

Since:

12.0

Author:

Marcin Mikosik

Constructor Summary

protected

FluentIterable() Constructor for use by subclasses.

Method Summary

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.
boolean	contains(Object element) Returns true if this fluent iterable contains any object for which equals(element) is true.
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.
boolean	isEmpty() Determines whether this fluent iterable is empty.
Optional<E>	last() Returns an Optional containing the last element in this fluent iterable.
FluentIterable<E>	limit(int size) Creates a fluent iterable with the first size elements of this fluent iterable.
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>	toImmutableList() Returns an ImmutableList containing all of the elements from this fluent iterable in proper sequence.
ImmutableSet<E>	toImmutableSet() Returns an ImmutableSet containing all of the elements from this fluent iterable with duplicates removed.
ImmutableSortedSet<E>	toImmutableSortedSet(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 comaprator.compare(x, y) == 0) removed.
ImmutableList<E>	toSortedImmutableList(Comparator<? super E> comparator) Returns an ImmutableList containing all of the elements from this FluentIterable in the order specified by comparator.
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<T>> function) Applies function to each element of this fluent iterable and returns a fluent iterable with the concatenated combination of results.

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

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.

from

@Deprecated
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.

toString

public String toString()

Returns a string representation of this fluent iterable, with the format [e1, e2, ..., en].

Overrides:

toString in class Object

size

public final int size()

Returns the number of elements in this fluent iterable.

contains

public final boolean contains(@Nullable
                              Object element)

Returns true if this fluent iterable contains any object for which equals(element) is true.

cycle

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.

filter

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().

filter

@GwtIncompatible(value="Class.isInstance")
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

anyMatch

public final boolean anyMatch(Predicate<? super E> predicate)

Returns true if any element in this fluent iterable satisfies the predicate.

allMatch

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.

firstMatch

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.

transform

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.

transformAndConcat

public <T> FluentIterable<T> transformAndConcat(Function<? super E,? extends Iterable<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.

Since:

13.0

first

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.

Throws:

NullPointerException - if the first element is null; if this is a possibility, use iterator().next() or Iterables.getFirst(java.lang.Iterable, T) instead.

last

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.

Throws:

NullPointerException - if the last element is null; if this is a possibility, use Iterables.getLast(java.lang.Iterable) instead.

skip

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.

limit

public final FluentIterable<E> limit(int size)

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.

Parameters:

size - the maximum number of elements in the returned fluent iterable

Throws:

IllegalArgumentException - if size is negative

isEmpty

public final boolean isEmpty()

Determines whether this fluent iterable is empty.

toImmutableList

public final ImmutableList<E> toImmutableList()

Returns an ImmutableList containing all of the elements from this fluent iterable in proper sequence.

toSortedImmutableList

public final ImmutableList<E> toSortedImmutableList(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 toSortedImmutableList(Ordering.natural()).

Parameters:

comparator - the function by which to sort list elements

Throws:

NullPointerException - if any element is null

Since:

13.0

toImmutableSet

public final ImmutableSet<E> toImmutableSet()

Returns an ImmutableSet containing all of the elements from this fluent iterable with duplicates removed.

toImmutableSortedSet

public final ImmutableSortedSet<E> toImmutableSortedSet(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 comaprator.compare(x, y) == 0) removed. To produce an ImmutableSortedSet sorted by its natural ordering, use toImmutableSortedSet(Ordering.natural()).

Parameters:

comparator - the function by which to sort set elements

Throws:

NullPointerException - if any element is null

toArray

@GwtIncompatible(value="Array.newArray(Class, int)")
public final E[] toArray(Class<E> type)

Returns an array containing all of the elements from this fluent iterable in iteration order.

Parameters:

type - the type of the elements

Returns:

a newly-allocated array into which all the elements of this fluent iterable have been copied

get

public final E get(int position)

Returns the element at the specified position in this fluent iterable.

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