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java.lang.Objectcom.google.common.collect.Iterables
@GwtCompatible(emulated=true) public final class Iterables
This class contains static utility methods that operate on or return objects
of type Iterable. Except as noted, each method has a corresponding
Iterator-based method in the Iterators class.
Performance notes: Unless otherwise noted, all of the iterables produced in this class are lazy, which means that their iterators only advance the backing iteration when absolutely necessary.
| Method Summary | ||
|---|---|---|
static
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addAll(Collection<T> addTo,
Iterable<? extends T> elementsToAdd)
Adds all elements in iterable to collection. |
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static
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all(Iterable<T> iterable,
Predicate<? super T> predicate)
Returns true if every element in iterable satisfies the
predicate. |
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static
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any(Iterable<T> iterable,
Predicate<? super T> predicate)
Returns true if one or more elements in iterable satisfy
the predicate. |
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static
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concat(Iterable<? extends Iterable<? extends T>> inputs)
Combines multiple iterables into a single iterable. |
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static
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concat(Iterable<? extends T>... inputs)
Combines multiple iterables into a single iterable. |
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static
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concat(Iterable<? extends T> a,
Iterable<? extends T> b)
Combines two iterables into a single iterable. |
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static
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concat(Iterable<? extends T> a,
Iterable<? extends T> b,
Iterable<? extends T> c)
Combines three iterables into a single iterable. |
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static
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concat(Iterable<? extends T> a,
Iterable<? extends T> b,
Iterable<? extends T> c,
Iterable<? extends T> d)
Combines four iterables into a single iterable. |
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static
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consumingIterable(Iterable<T> iterable)
Returns a view of the supplied iterable that wraps each generated Iterator through Iterators.consumingIterator(Iterator). |
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static boolean |
contains(Iterable<?> iterable,
Object element)
Returns true if iterable contains element; that is,
any object for which equals(element) is true. |
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static
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cycle(Iterable<T> iterable)
Returns an iterable whose iterators cycle indefinitely over the elements of iterable. |
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static
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cycle(T... elements)
Returns an iterable whose iterators cycle indefinitely over the provided elements. |
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static boolean |
elementsEqual(Iterable<?> iterable1,
Iterable<?> iterable2)
Determines whether two iterables contain equal elements in the same order. |
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static
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filter(Iterable<?> unfiltered,
Class<T> type)
Returns all instances of class type in unfiltered. |
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static
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filter(Iterable<T> unfiltered,
Predicate<? super T> predicate)
Returns the elements of unfiltered that satisfy a predicate. |
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static
|
find(Iterable<T> iterable,
Predicate<? super T> predicate)
Returns the first element in iterable that satisfies the given
predicate; use this method only when such an element is known to exist. |
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static
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find(Iterable<T> iterable,
Predicate<? super T> predicate,
T defaultValue)
Returns the first element in iterable that satisfies the given
predicate, or defaultValue if none found. |
|
static int |
frequency(Iterable<?> iterable,
Object element)
Returns the number of elements in the specified iterable that equal the specified object. |
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static
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get(Iterable<T> iterable,
int position)
Returns the element at the specified position in an iterable. |
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static
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get(Iterable<T> iterable,
int position,
T defaultValue)
Returns the element at the specified position in an iterable or a default value otherwise. |
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static
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getFirst(Iterable<T> iterable,
T defaultValue)
Returns the first element in iterable or defaultValue if
the iterable is empty. |
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static
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getLast(Iterable<T> iterable)
Returns the last element of iterable. |
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static
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getLast(Iterable<T> iterable,
T defaultValue)
Returns the last element of iterable or defaultValue if
the iterable is empty. |
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static
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getOnlyElement(Iterable<T> iterable)
Returns the single element contained in iterable. |
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static
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getOnlyElement(Iterable<T> iterable,
T defaultValue)
Returns the single element contained in iterable, or defaultValue if the iterable is empty. |
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static
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indexOf(Iterable<T> iterable,
Predicate<? super T> predicate)
Returns the index in iterable of the first element that satisfies
the provided predicate, or -1 if the Iterable has no such
elements. |
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static boolean |
isEmpty(Iterable<?> iterable)
Determines if the given iterable contains no elements. |
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static
|
limit(Iterable<T> iterable,
int limitSize)
Creates an iterable with the first limitSize elements of the given
iterable. |
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static
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mergeSorted(Iterable<? extends Iterable<? extends T>> iterables,
Comparator<? super T> comparator)
Returns an iterable over the merged contents of all given iterables. |
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static
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paddedPartition(Iterable<T> iterable,
int size)
Divides an iterable into unmodifiable sublists of the given size, padding the final iterable with null values if necessary. |
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static
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partition(Iterable<T> iterable,
int size)
Divides an iterable into unmodifiable sublists of the given size (the final iterable may be smaller). |
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static boolean |
removeAll(Iterable<?> removeFrom,
Collection<?> elementsToRemove)
Removes, from an iterable, every element that belongs to the provided collection. |
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static
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removeIf(Iterable<T> removeFrom,
Predicate<? super T> predicate)
Removes, from an iterable, every element that satisfies the provided predicate. |
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static boolean |
retainAll(Iterable<?> removeFrom,
Collection<?> elementsToRetain)
Removes, from an iterable, every element that does not belong to the provided collection. |
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static
|
reverse(List<T> list)
Deprecated. use Lists.reverse(List) or ImmutableList.reverse(). This method is scheduled for deletion in
July 2012. |
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static int |
size(Iterable<?> iterable)
Returns the number of elements in iterable. |
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static
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skip(Iterable<T> iterable,
int numberToSkip)
Returns a view of iterable that skips its first
numberToSkip elements. |
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static
|
toArray(Iterable<? extends T> iterable,
Class<T> type)
Copies an iterable's elements into an array. |
|
static String |
toString(Iterable<?> iterable)
Returns a string representation of iterable, with the format
[e1, e2, ..., en]. |
|
static
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transform(Iterable<F> fromIterable,
Function<? super F,? extends T> function)
Returns an iterable that applies function to each element of fromIterable. |
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static
|
tryFind(Iterable<T> iterable,
Predicate<? super T> predicate)
Returns an Optional containing the first element in iterable that satisfies the given predicate, if such an element exists. |
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static
|
unmodifiableIterable(ImmutableCollection<E> iterable)
Deprecated. no need to use this |
|
static
|
unmodifiableIterable(Iterable<T> iterable)
Returns an unmodifiable view of iterable. |
|
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Method Detail |
|---|
public static <T> Iterable<T> unmodifiableIterable(Iterable<T> iterable)
iterable.
@Deprecated public static <E> Iterable<E> unmodifiableIterable(ImmutableCollection<E> iterable)
public static int size(Iterable<?> iterable)
iterable.
public static boolean contains(Iterable<?> iterable,
@Nullable
Object element)
true if iterable contains element; that is,
any object for which equals(element) is true.
public static boolean removeAll(Iterable<?> removeFrom,
Collection<?> elementsToRemove)
This method calls Collection.removeAll(java.util.Collection>) if iterable is a
collection, and Iterators.removeAll(java.util.Iterator>, java.util.Collection>) otherwise.
removeFrom - the iterable to (potentially) remove elements fromelementsToRemove - the elements to remove
true if any element was removed from iterable
public static boolean retainAll(Iterable<?> removeFrom,
Collection<?> elementsToRetain)
This method calls Collection.retainAll(java.util.Collection>) if iterable is a
collection, and Iterators.retainAll(java.util.Iterator>, java.util.Collection>) otherwise.
removeFrom - the iterable to (potentially) remove elements fromelementsToRetain - the elements to retain
true if any element was removed from iterable
public static <T> boolean removeIf(Iterable<T> removeFrom,
Predicate<? super T> predicate)
removeFrom - the iterable to (potentially) remove elements frompredicate - a predicate that determines whether an element should
be removed
true if any elements were removed from the iterable
UnsupportedOperationException - if the iterable does not support
remove().
public static boolean elementsEqual(Iterable<?> iterable1,
Iterable<?> iterable2)
true if iterable1
and iterable2 contain the same number of elements and every element
of iterable1 is equal to the corresponding element of
iterable2.
public static String toString(Iterable<?> iterable)
iterable, with the format
[e1, e2, ..., en].
public static <T> T getOnlyElement(Iterable<T> iterable)
iterable.
NoSuchElementException - if the iterable is empty
IllegalArgumentException - if the iterable contains multiple
elements
public static <T> T getOnlyElement(Iterable<T> iterable,
@Nullable
T defaultValue)
iterable, or defaultValue if the iterable is empty.
IllegalArgumentException - if the iterator contains multiple
elements
@GwtIncompatible(value="Array.newInstance(Class, int)")
public static <T> T[] toArray(Iterable<? extends T> iterable,
Class<T> type)
iterable - the iterable to copytype - the type of the elements
public static <T> boolean addAll(Collection<T> addTo,
Iterable<? extends T> elementsToAdd)
iterable to collection.
true if collection was modified as a result of this
operation.
public static int frequency(Iterable<?> iterable,
@Nullable
Object element)
Multiset or Set.
Collections.frequency(java.util.Collection>, java.lang.Object)public static <T> Iterable<T> cycle(Iterable<T> iterable)
iterable.
That 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.
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.
To cycle over the iterable n times, use the following:
Iterables.concat(Collections.nCopies(n, iterable))
public static <T> Iterable<T> cycle(T... elements)
After remove is invoked on a generated iterator, the removed
element will no longer appear in either that iterator or any other iterator
created from the same source iterable. That is, this method behaves exactly
as Iterables.cycle(Lists.newArrayList(elements)). The iterator's
hasNext method returns true until all of the original
elements have been removed.
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.
To cycle over the elements n times, use the following:
Iterables.concat(Collections.nCopies(n, Arrays.asList(elements)))
public static <T> Iterable<T> concat(Iterable<? extends T> a,
Iterable<? extends T> b)
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.
public static <T> Iterable<T> concat(Iterable<? extends T> a,
Iterable<? extends T> b,
Iterable<? extends T> c)
a, followed by the
elements in b, followed by the elements in c. The source
iterators are not polled until necessary.
The returned iterable's iterator supports remove() when the
corresponding input iterator supports it.
public static <T> Iterable<T> concat(Iterable<? extends T> a,
Iterable<? extends T> b,
Iterable<? extends T> c,
Iterable<? extends T> d)
a, followed by the
elements in b, followed by the elements in c, followed by
the elements in d. The source iterators are not polled until
necessary.
The returned iterable's iterator supports remove() when the
corresponding input iterator supports it.
public static <T> Iterable<T> concat(Iterable<? extends T>... inputs)
inputs. The input iterators are not polled until necessary.
The returned iterable's iterator supports remove() when the
corresponding input iterator supports it.
NullPointerException - if any of the provided iterables is nullpublic static <T> Iterable<T> concat(Iterable<? extends Iterable<? extends T>> inputs)
inputs. The input iterators are not polled until necessary.
The returned iterable's iterator supports remove() when the
corresponding input iterator supports it. The methods of the returned
iterable may throw NullPointerException if any of the input
iterators is null.
public static <T> Iterable<List<T>> partition(Iterable<T> iterable,
int size)
[a, b, c, d, e] with a partition size of 3 yields [[a, b, c], [d, e]] -- an outer iterable containing two inner lists of
three and two elements, all in the original order.
Iterators returned by the returned iterable do not support the Iterator.remove() method. The returned lists implement RandomAccess, whether or not the input list does.
Note: if iterable is a List, use Lists.partition(List, int) instead.
iterable - the iterable to return a partitioned view ofsize - the desired size of each partition (the last may be smaller)
iterable divided into partitions
IllegalArgumentException - if size is nonpositive
public static <T> Iterable<List<T>> paddedPartition(Iterable<T> iterable,
int size)
[a, b, c, d, e] with a partition size of 3
yields [[a, b, c], [d, e, null]] -- an outer iterable containing
two inner lists of three elements each, all in the original order.
Iterators returned by the returned iterable do not support the Iterator.remove() method.
iterable - the iterable to return a partitioned view ofsize - the desired size of each partition
iterable divided into partitions (the final iterable may have
trailing null elements)
IllegalArgumentException - if size is nonpositive
public static <T> Iterable<T> filter(Iterable<T> unfiltered,
Predicate<? super T> predicate)
unfiltered that satisfy a predicate. The
resulting iterable's iterator does not support remove().
@GwtIncompatible(value="Class.isInstance")
public static <T> Iterable<T> filter(Iterable<?> unfiltered,
Class<T> type)
type in unfiltered. The
returned iterable has elements whose class is type or a subclass of
type. The returned iterable's iterator does not support
remove().
unfiltered - an iterable containing objects of any typetype - the type of elements desired
public static <T> boolean any(Iterable<T> iterable,
Predicate<? super T> predicate)
true if one or more elements in iterable satisfy
the predicate.
public static <T> boolean all(Iterable<T> iterable,
Predicate<? super T> predicate)
true if every element in iterable satisfies the
predicate. If iterable is empty, true is returned.
public static <T> T find(Iterable<T> iterable,
Predicate<? super T> predicate)
iterable that satisfies the given
predicate; use this method only when such an element is known to exist. If
it is possible that no element will match, use #tryFind) or #find(Iterable, Predicate, T) instead.
NoSuchElementException - if no element in iterable matches
the given predicate
public static <T> T find(Iterable<T> iterable,
Predicate<? super T> predicate,
@Nullable
T defaultValue)
iterable that satisfies the given
predicate, or defaultValue if none found. Note that this can
usually be handled more naturally using tryFind(iterable, predicate).or(defaultValue).
public static <T> Optional<T> tryFind(Iterable<T> iterable,
Predicate<? super T> predicate)
Optional containing the first element in iterable that satisfies the given predicate, if such an element exists.
Warning: avoid using a predicate that matches null. If null is matched in iterable, a
NullPointerException will be thrown.
public static <T> int indexOf(Iterable<T> iterable,
Predicate<? super T> predicate)
iterable of the first element that satisfies
the provided predicate, or -1 if the Iterable has no such
elements.
More formally, returns the lowest index i such that
predicate.apply(Iterables.get(iterable, i)) returns true,
or -1 if there is no such index.
public static <F,T> Iterable<T> transform(Iterable<F> fromIterable,
Function<? super F,? extends T> function)
function to each element of fromIterable.
The returned iterable's iterator supports remove() if the
provided iterator does. After a successful remove() call,
fromIterable no longer contains the corresponding element.
If the input Iterable is known to be a List or other
Collection, consider Lists.transform(java.util.List and Collections2.transform(java.util.Collection.
public static <T> T get(Iterable<T> iterable,
int position)
position - position of the element to return
iterable
IndexOutOfBoundsException - if position is negative or
greater than or equal to the size of iterable
public static <T> T get(Iterable<T> iterable,
int position,
@Nullable
T defaultValue)
position - position of the element to returndefaultValue - the default value to return if position is
greater than or equal to the size of the iterable
iterable or
defaultValue if iterable contains fewer than
position + 1 elements.
IndexOutOfBoundsException - if position is negative
public static <T> T getFirst(Iterable<T> iterable,
@Nullable
T defaultValue)
iterable or defaultValue if
the iterable is empty. The Iterators analog to this method is
Iterators.getNext(java.util.Iterator, T) .
defaultValue - the default value to return if the iterable is empty
iterable or the default valuepublic static <T> T getLast(Iterable<T> iterable)
iterable.
iterable
NoSuchElementException - if the iterable is empty
public static <T> T getLast(Iterable<T> iterable,
@Nullable
T defaultValue)
iterable or defaultValue if
the iterable is empty.
defaultValue - the value to return if iterable is empty
iterable or the default value
public static <T> Iterable<T> skip(Iterable<T> iterable,
int numberToSkip)
iterable that skips its first
numberToSkip elements. If iterable contains fewer than
numberToSkip elements, the returned iterable skips all of its
elements.
Modifications to the underlying Iterable before a call to
iterator() are reflected in the returned iterator. That is, the
iterator skips the first numberToSkip elements that exist when the
Iterator is created, not when skip() is called.
The returned iterable's iterator supports remove() if the
iterator of the underlying iterable supports it. Note that it is
not possible to delete the last skipped element by immediately
calling remove() on that iterator, as the Iterator
contract states that a call to remove() before a call to
next() will throw an IllegalStateException.
public static <T> Iterable<T> limit(Iterable<T> iterable,
int limitSize)
limitSize elements of the given
iterable. If the original iterable does not contain that many elements, the
returned iterator will have the same behavior as the original iterable. The
returned iterable's iterator supports remove() if the original
iterator does.
iterable - the iterable to limitlimitSize - the maximum number of elements in the returned iterator
IllegalArgumentException - if limitSize is negativepublic static <T> Iterable<T> consumingIterable(Iterable<T> iterable)
Iterator through Iterators.consumingIterator(Iterator).
Note: If iterable is a Queue, the returned iterable will
get entries from Queue.remove() since Queue's iteration
order is undefined. Calling Iterator.hasNext() on a generated
iterator from the returned iterable may cause an item to be immediately
dequeued for return on a subsequent call to Iterator.next().
iterable - the iterable to wrap
Iterators.consumingIterator(Iterator); for queues,
an iterable that generates iterators that return and consume the
queue's elements in queue orderIterators.consumingIterator(Iterator)@Deprecated public static <T> Iterable<T> reverse(List<T> list)
Lists.reverse(List) or ImmutableList.reverse(). This method is scheduled for deletion in
July 2012.
List<String> mylist = ...
for (String str : Iterables.reverse(mylist)) {
...
}
There is no corresponding method in Iterators, since Iterable.iterator() can simply be invoked on the result of calling this
method.
public static boolean isEmpty(Iterable<?> iterable)
There is no precise Iterator equivalent to this method, since
one can only ask an iterator whether it has any elements remaining
(which one does using Iterator.hasNext()).
true if the iterable contains no elements
@Beta
public static <T> Iterable<T> mergeSorted(Iterable<? extends Iterable<? extends T>> iterables,
Comparator<? super T> comparator)
iterables. Equivalent entries will not be de-duplicated.
Callers must ensure that the source iterables are in
non-descending order as this method does not sort its input.
For any equivalent elements across all iterables, it is
undefined which element is returned first.
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