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java.lang.Objectcom.google.common.collect.Collections2
@GwtCompatible public final class Collections2
Provides static methods for working with Collection instances.
| Method Summary | ||
|---|---|---|
static
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filter(Collection<E> unfiltered,
Predicate<? super E> predicate)
Returns the elements of unfiltered that satisfy a predicate. |
|
static
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transform(Collection<F> fromCollection,
Function<? super F,T> function)
Returns a collection that applies function to each element of
fromCollection. |
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| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Method Detail |
|---|
public static <E> Collection<E> filter(Collection<E> unfiltered,
Predicate<? super E> predicate)
unfiltered that satisfy a predicate. The
returned collection is a live view of unfiltered; changes to one
affect the other.
The resulting collection's iterator does not support remove(),
but all other collection methods are supported. When given an element that
doesn't satisfy the predicate, the collection's add() and addAll() methods throw an IllegalArgumentException. When methods
such as removeAll() and clear() are called on the filtered
collection, only elements that satisfy the filter will be removed from the
underlying collection.
The returned collection isn't threadsafe or serializable, even if
unfiltered is.
Many of the filtered collection's methods, such as size(),
iterate across every element in the underlying collection and determine
which elements satisfy the filter. When a live view is not needed,
it may be faster to copy Iterables.filter(unfiltered, predicate)
and use the copy.
Warning: predicate must be consistent with equals,
as documented at Predicate.apply(T). Do not provide a predicate such
as Predicates.instanceOf(ArrayList.class), which is inconsistent
with equals. (See Iterables.filter(Iterable, Class) for related
functionality.)
public static <F,T> Collection<T> transform(Collection<F> fromCollection,
Function<? super F,T> function)
function to each element of
fromCollection. The returned collection is a live view of fromCollection; changes to one affect the other.
The returned collection's add() and addAll() methods
throw an UnsupportedOperationException. All other collection
methods are supported, as long as fromCollection supports them.
The returned collection isn't threadsafe or serializable, even if
fromCollection is.
When a live view is not needed, it may be faster to copy the transformed collection and use the copy.
If the input Collection is known to be a List, consider
Lists.transform(java.util.List. If only an Iterable is available, use
Iterables.transform(java.lang.Iterable.
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