Modifier and Type  Class and Description 

static class 
Sets.SetView<E>
An unmodifiable view of a set which may be backed by other sets; this view will change as the
backing sets do.

Modifier and Type  Method and Description 

static <B> Set<List<B>> 
cartesianProduct(List<? extends Set<? extends B>> sets)
Returns every possible list that can be formed by choosing one element from each of the given
sets in order; the "nary Cartesian
product" of the sets.

static <B> Set<List<B>> 
cartesianProduct(Set<? extends B>... sets)
Returns every possible list that can be formed by choosing one element from each of the given
sets in order; the "nary Cartesian
product" of the sets.

static <E> Set<Set<E>> 
combinations(Set<E> set,
int size)
Returns the set of all subsets of
set of size size . 
static <E extends Enum<E>> 
complementOf(Collection<E> collection)
Creates an
EnumSet consisting of all enum values that are not in the specified
collection. 
static <E extends Enum<E>> 
complementOf(Collection<E> collection,
Class<E> type)
Creates an
EnumSet consisting of all enum values that are not in the specified
collection. 
static <E> Sets.SetView<E> 
difference(Set<E> set1,
Set<?> set2)
Returns an unmodifiable view of the difference of two sets.

static <E> NavigableSet<E> 
filter(NavigableSet<E> unfiltered,
Predicate<? super E> predicate)
Returns the elements of a
NavigableSet , unfiltered , that satisfy a predicate. 
static <E> Set<E> 
filter(Set<E> unfiltered,
Predicate<? super E> predicate)
Returns the elements of
unfiltered that satisfy a predicate. 
static <E> SortedSet<E> 
filter(SortedSet<E> unfiltered,
Predicate<? super E> predicate)
Returns the elements of a
SortedSet , unfiltered , that satisfy a predicate. 
static <E extends Enum<E>> 
immutableEnumSet(E anElement,
E... otherElements)
Returns an immutable set instance containing the given enum elements.

static <E extends Enum<E>> 
immutableEnumSet(Iterable<E> elements)
Returns an immutable set instance containing the given enum elements.

static <E> Sets.SetView<E> 
intersection(Set<E> set1,
Set<?> set2)
Returns an unmodifiable view of the intersection of two sets.

static <E> Set<E> 
newConcurrentHashSet()
Creates a threadsafe set backed by a hash map.

static <E> Set<E> 
newConcurrentHashSet(Iterable<? extends E> elements)
Creates a threadsafe set backed by a hash map and containing the given elements.

static <E> CopyOnWriteArraySet<E> 
newCopyOnWriteArraySet()
Creates an empty
CopyOnWriteArraySet instance. 
static <E> CopyOnWriteArraySet<E> 
newCopyOnWriteArraySet(Iterable<? extends E> elements)
Creates a
CopyOnWriteArraySet instance containing the given elements. 
static <E extends Enum<E>> 
newEnumSet(Iterable<E> iterable,
Class<E> elementType)
Returns a new, mutable
EnumSet instance containing the given elements in their
natural order. 
static <E> HashSet<E> 
newHashSet()
Creates a mutable, initially empty
HashSet instance. 
static <E> HashSet<E> 
newHashSet(E... elements)
Creates a mutable
HashSet instance initially containing the given elements. 
static <E> HashSet<E> 
newHashSet(Iterable<? extends E> elements)
Creates a mutable
HashSet instance containing the given elements. 
static <E> HashSet<E> 
newHashSet(Iterator<? extends E> elements)
Creates a mutable
HashSet instance containing the given elements. 
static <E> HashSet<E> 
newHashSetWithExpectedSize(int expectedSize)
Returns a new hash set using the smallest initial table size that can hold
expectedSize
elements without resizing. 
static <E> Set<E> 
newIdentityHashSet()
Creates an empty
Set that uses identity to determine equality. 
static <E> LinkedHashSet<E> 
newLinkedHashSet()
Creates a mutable, empty
LinkedHashSet instance. 
static <E> LinkedHashSet<E> 
newLinkedHashSet(Iterable<? extends E> elements)
Creates a mutable
LinkedHashSet instance containing the given elements in order. 
static <E> LinkedHashSet<E> 
newLinkedHashSetWithExpectedSize(int expectedSize)
Creates a
LinkedHashSet instance, with a high enough "initial capacity" that it
should hold expectedSize elements without growth. 
static <E> Set<E> 
newSetFromMap(Map<E,Boolean> map)
Deprecated.

static <E extends Comparable> 
newTreeSet()
Creates a mutable, empty
TreeSet instance sorted by the natural sort ordering of
its elements. 
static <E> TreeSet<E> 
newTreeSet(Comparator<? super E> comparator)
Creates a mutable, empty
TreeSet instance with the given comparator. 
static <E extends Comparable> 
newTreeSet(Iterable<? extends E> elements)
Creates a mutable
TreeSet instance containing the given elements sorted by their
natural ordering. 
static <E> Set<Set<E>> 
powerSet(Set<E> set)
Returns the set of all possible subsets of
set . 
static <K extends Comparable<? super K>> 
subSet(NavigableSet<K> set,
Range<K> range)
Returns a view of the portion of
set whose elements are contained by range . 
static <E> Sets.SetView<E> 
symmetricDifference(Set<? extends E> set1,
Set<? extends E> set2)
Returns an unmodifiable view of the symmetric difference of two sets.

static <E> NavigableSet<E> 
synchronizedNavigableSet(NavigableSet<E> navigableSet)
Returns a synchronized (threadsafe) navigable set backed by the specified navigable set.

static <E> Sets.SetView<E> 
union(Set<? extends E> set1,
Set<? extends E> set2)
Returns an unmodifiable view of the union of two sets.

static <E> NavigableSet<E> 
unmodifiableNavigableSet(NavigableSet<E> set)
Returns an unmodifiable view of the specified navigable set.

@GwtCompatible(serializable=true) public static <E extends Enum<E>> ImmutableSet<E> immutableEnumSet(E anElement, E... otherElements)
EnumSet
.
The iteration order of the returned set follows the enum's iteration order, not the order in which the elements are provided to the method.
anElement
 one of the elements the set should containotherElements
 the rest of the elements the set should contain@GwtCompatible(serializable=true) public static <E extends Enum<E>> ImmutableSet<E> immutableEnumSet(Iterable<E> elements)
EnumSet
.
The iteration order of the returned set follows the enum's iteration order, not the order in which the elements appear in the given collection.
elements
 the elements, all of the same enum
type, that the set should containpublic static <E extends Enum<E>> EnumSet<E> newEnumSet(Iterable<E> iterable, Class<E> elementType)
EnumSet
instance containing the given elements in their
natural order. This method behaves identically to EnumSet.copyOf(Collection)
, but also
accepts nonCollection
iterables and empty iterables.public static <E> HashSet<E> newHashSet()
HashSet
instance.
Note: if mutability is not required, use ImmutableSet.of()
instead. If E
is an Enum
type, use EnumSet.noneOf(java.lang.Class<E>)
instead. Otherwise, strongly consider
using a LinkedHashSet
instead, at the cost of increased memory footprint, to get
deterministic iteration behavior.
Note for Java 7 and later: this method is now unnecessary and should be treated as
deprecated. Instead, use the HashSet
constructor directly, taking advantage of the new
"diamond" syntax.
public static <E> HashSet<E> newHashSet(E... elements)
HashSet
instance initially containing the given elements.
Note: if elements are nonnull and won't be added or removed after this point, use
ImmutableSet.of()
or ImmutableSet.copyOf(Object[])
instead. If E
is an
Enum
type, use EnumSet.of(Enum, Enum[])
instead. Otherwise, strongly consider
using a LinkedHashSet
instead, at the cost of increased memory footprint, to get
deterministic iteration behavior.
This method is just a small convenience, either for newHashSet(
asList
(...))
, or for creating an empty set then calling Collections.addAll(java.util.Collection<? super T>, T...)
.
This method is not actually very useful and will likely be deprecated in the future.
public static <E> HashSet<E> newHashSet(Iterable<? extends E> elements)
HashSet
instance containing the given elements. A very thin
convenience for creating an empty set then calling Collection.addAll(java.util.Collection<? extends E>)
or Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)
.
Note: if mutability is not required and the elements are nonnull, use ImmutableSet.copyOf(Iterable)
instead. (Or, change elements
to be a FluentIterable
and call elements.toSet()
.)
Note: if E
is an Enum
type, use newEnumSet(Iterable, Class)
instead.
Note for Java 7 and later: if elements
is a Collection
, you don't
need this method. Instead, use the HashSet
constructor directly, taking advantage of
the new "diamond" syntax.
Overall, this method is not very useful and will likely be deprecated in the future.
public static <E> HashSet<E> newHashSet(Iterator<? extends E> elements)
HashSet
instance containing the given elements. A very thin
convenience for creating an empty set and then calling Iterators.addAll(java.util.Collection<T>, java.util.Iterator<? extends T>)
.
Note: if mutability is not required and the elements are nonnull, use ImmutableSet.copyOf(Iterator)
instead.
Note: if E
is an Enum
type, you should create an EnumSet
instead.
Overall, this method is not very useful and will likely be deprecated in the future.
public static <E> HashSet<E> newHashSetWithExpectedSize(int expectedSize)
expectedSize
elements without resizing. Note that this is not what HashSet.HashSet(int)
does, but it
is what most users want and expect it to do.
This behavior can't be broadly guaranteed, but has been tested with OpenJDK 1.7 and 1.8.
expectedSize
 the number of elements you expect to add to the returned setexpectedSize
elements
without resizingIllegalArgumentException
 if expectedSize
is negativepublic static <E> Set<E> newConcurrentHashSet()
ConcurrentHashMap
instance, and thus carries the same concurrency guarantees.
Unlike HashSet
, this class does NOT allow null
to be used as an element. The
set is serializable.
Set
public static <E> Set<E> newConcurrentHashSet(Iterable<? extends E> elements)
ConcurrentHashMap
instance, and thus carries the same concurrency
guarantees.
Unlike HashSet
, this class does NOT allow null
to be used as an element. The
set is serializable.
elements
 the elements that the set should containNullPointerException
 if elements
or any of its contents is nullpublic static <E> LinkedHashSet<E> newLinkedHashSet()
LinkedHashSet
instance.
Note: if mutability is not required, use ImmutableSet.of()
instead.
Note for Java 7 and later: this method is now unnecessary and should be treated as
deprecated. Instead, use the LinkedHashSet
constructor directly, taking advantage of
the new "diamond" syntax.
LinkedHashSet
public static <E> LinkedHashSet<E> newLinkedHashSet(Iterable<? extends E> elements)
LinkedHashSet
instance containing the given elements in order.
Note: if mutability is not required and the elements are nonnull, use ImmutableSet.copyOf(Iterable)
instead.
Note for Java 7 and later: if elements
is a Collection
, you don't
need this method. Instead, use the LinkedHashSet
constructor directly, taking advantage
of the new "diamond" syntax.
Overall, this method is not very useful and will likely be deprecated in the future.
elements
 the elements that the set should contain, in orderLinkedHashSet
containing those elements (minus duplicates)public static <E> LinkedHashSet<E> newLinkedHashSetWithExpectedSize(int expectedSize)
LinkedHashSet
instance, with a high enough "initial capacity" that it
should hold expectedSize
elements without growth. This behavior cannot be
broadly guaranteed, but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed
that the method isn't inadvertently oversizing the returned set.expectedSize
 the number of elements you expect to add to the returned setLinkedHashSet
with enough capacity to hold expectedSize
elements without resizingIllegalArgumentException
 if expectedSize
is negativepublic static <E extends Comparable> TreeSet<E> newTreeSet()
TreeSet
instance sorted by the natural sort ordering of
its elements.
Note: if mutability is not required, use ImmutableSortedSet.of()
instead.
Note for Java 7 and later: this method is now unnecessary and should be treated as
deprecated. Instead, use the TreeSet
constructor directly, taking advantage of the new
"diamond" syntax.
TreeSet
public static <E extends Comparable> TreeSet<E> newTreeSet(Iterable<? extends E> elements)
TreeSet
instance containing the given elements sorted by their
natural ordering.
Note: if mutability is not required, use ImmutableSortedSet.copyOf(Iterable)
instead.
Note: If elements
is a SortedSet
with an explicit comparator, this
method has different behavior than TreeSet.TreeSet(SortedSet)
, which returns a TreeSet
with that comparator.
Note for Java 7 and later: this method is now unnecessary and should be treated as
deprecated. Instead, use the TreeSet
constructor directly, taking advantage of the new
"diamond" syntax.
This method is just a small convenience for creating an empty set and then calling Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)
. This method is not very useful and will likely be deprecated in the future.
elements
 the elements that the set should containTreeSet
containing those elements (minus duplicates)public static <E> TreeSet<E> newTreeSet(Comparator<? super E> comparator)
TreeSet
instance with the given comparator.
Note: if mutability is not required, use ImmutableSortedSet.orderedBy(comparator).build()
instead.
Note for Java 7 and later: this method is now unnecessary and should be treated as
deprecated. Instead, use the TreeSet
constructor directly, taking advantage of the new
"diamond" syntax. One caveat to this is that the TreeSet
constructor uses a null Comparator
to mean "natural ordering," whereas this
factory rejects null. Clean your code accordingly.
comparator
 the comparator to use to sort the setTreeSet
NullPointerException
 if comparator
is nullpublic static <E> Set<E> newIdentityHashSet()
Set
that uses identity to determine equality. It compares object
references, instead of calling equals
, to determine whether a provided object matches
an element in the set. For example, contains
returns false
when passed an
object that equals a set member, but isn't the same instance. This behavior is similar to the
way IdentityHashMap
handles key lookups.@GwtIncompatible public static <E> CopyOnWriteArraySet<E> newCopyOnWriteArraySet()
CopyOnWriteArraySet
instance.
Note: if you need an immutable empty Set
, use Collections.emptySet()
instead.
CopyOnWriteArraySet
@GwtIncompatible public static <E> CopyOnWriteArraySet<E> newCopyOnWriteArraySet(Iterable<? extends E> elements)
CopyOnWriteArraySet
instance containing the given elements.elements
 the elements that the set should contain, in orderCopyOnWriteArraySet
containing those elementspublic static <E extends Enum<E>> EnumSet<E> complementOf(Collection<E> collection)
EnumSet
consisting of all enum values that are not in the specified
collection. If the collection is an EnumSet
, this method has the same behavior as
EnumSet.complementOf(java.util.EnumSet<E>)
. Otherwise, the specified collection must contain at least one
element, in order to determine the element type. If the collection could be empty, use complementOf(Collection, Class)
instead of this method.collection
 the collection whose complement should be stored in the enum setEnumSet
containing all values of the enum that aren't present
in the given collectionIllegalArgumentException
 if collection
is not an EnumSet
instance and
contains no elementspublic static <E extends Enum<E>> EnumSet<E> complementOf(Collection<E> collection, Class<E> type)
EnumSet
consisting of all enum values that are not in the specified
collection. This is equivalent to EnumSet.complementOf(java.util.EnumSet<E>)
, but can act on any input
collection, as long as the elements are of enum type.collection
 the collection whose complement should be stored in the EnumSet
type
 the type of the elements in the setEnumSet
initially containing all the values of the enum not
present in the given collection@Deprecated public static <E> Set<E> newSetFromMap(Map<E,Boolean> map)
Collections.newSetFromMap(java.util.Map<E, java.lang.Boolean>)
instead.Set
implementation corresponding to any Map
implementation.
There is no need to use this method on a Map
implementation that already has a
corresponding Set
implementation (such as HashMap
or TreeMap
).
Each method invocation on the set returned by this method results in exactly one method
invocation on the backing map or its keySet
view, with one exception. The addAll
method is implemented as a sequence of put
invocations on the backing map.
The specified map must be empty at the time this method is invoked, and should not be accessed directly after this method returns. These conditions are ensured if the map is created empty, passed directly to this method, and no reference to the map is retained, as illustrated in the following code fragment:
Set<Object> identityHashSet = Sets.newSetFromMap(
new IdentityHashMap<Object, Boolean>());
The returned set is serializable if the backing map is.
map
 the backing mapIllegalArgumentException
 if map
is not emptypublic static <E> Sets.SetView<E> union(Set<? extends E> set1, Set<? extends E> set2)
set1
, then over each element of set2
, in order,
that is not contained in set1
.
Results are undefined if set1
and set2
are sets based on different
equivalence relations (as HashSet
, TreeSet
, and the Map.keySet()
of an
IdentityHashMap
all are).
public static <E> Sets.SetView<E> intersection(Set<E> set1, Set<?> set2)
set1
.
Results are undefined if set1
and set2
are sets based on different
equivalence relations (as HashSet
, TreeSet
, and the keySet of an IdentityHashMap
all are).
Note: The returned view performs slightly better when set1
is the smaller of
the two sets. If you have reason to believe one of your sets will generally be smaller than the
other, pass it first. Unfortunately, since this method sets the generic type of the returned
set based on the type of the first set passed, this could in rare cases force you to make a
cast, for example:
Set<Object> aFewBadObjects = ...
Set<String> manyBadStrings = ...
// impossible for a nonString to be in the intersection
SuppressWarnings("unchecked")
Set<String> badStrings = (Set) Sets.intersection(
aFewBadObjects, manyBadStrings);
This is unfortunate, but should come up only very rarely.
public static <E> Sets.SetView<E> difference(Set<E> set1, Set<?> set2)
set1
and not contained by set2
. set2
may also contain elements not present in set1
; these are simply ignored. The iteration
order of the returned set matches that of set1
.
Results are undefined if set1
and set2
are sets based on different
equivalence relations (as HashSet
, TreeSet
, and the keySet of an IdentityHashMap
all are).
public static <E> Sets.SetView<E> symmetricDifference(Set<? extends E> set1, Set<? extends E> set2)
set1
or set2
but not in
both. The iteration order of the returned set is undefined.
Results are undefined if set1
and set2
are sets based on different
equivalence relations (as HashSet
, TreeSet
, and the keySet of an IdentityHashMap
all are).
public static <E> Set<E> filter(Set<E> unfiltered, Predicate<? super E> predicate)
unfiltered
that satisfy a predicate. The returned set is a live
view of unfiltered
; changes to one affect the other.
The resulting set's iterator does not support remove()
, but all other set methods
are supported. When given an element that doesn't satisfy the predicate, the set's add()
and addAll()
methods throw an IllegalArgumentException
. When methods
such as removeAll()
and clear()
are called on the filtered set, only elements
that satisfy the filter will be removed from the underlying set.
The returned set isn't threadsafe or serializable, even if unfiltered
is.
Many of the filtered set's methods, such as size()
, iterate across every element in
the underlying set 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.)
Java 8 users: many use cases for this method are better addressed by Stream.filter(java.util.function.Predicate<? super T>)
. This method is not being deprecated, but we gently encourage
you to migrate to streams.
public static <E> SortedSet<E> filter(SortedSet<E> unfiltered, Predicate<? super E> predicate)
SortedSet
, unfiltered
, that satisfy a predicate. The
returned set is a live view of unfiltered
; changes to one affect the other.
The resulting set's iterator does not support remove()
, but all other set methods
are supported. When given an element that doesn't satisfy the predicate, the set's add()
and addAll()
methods throw an IllegalArgumentException
. When methods
such as removeAll()
and clear()
are called on the filtered set, only elements
that satisfy the filter will be removed from the underlying set.
The returned set isn't threadsafe or serializable, even if unfiltered
is.
Many of the filtered set's methods, such as size()
, iterate across every element in
the underlying set 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.)
@GwtIncompatible public static <E> NavigableSet<E> filter(NavigableSet<E> unfiltered, Predicate<? super E> predicate)
NavigableSet
, unfiltered
, that satisfy a predicate.
The returned set is a live view of unfiltered
; changes to one affect the other.
The resulting set's iterator does not support remove()
, but all other set methods
are supported. When given an element that doesn't satisfy the predicate, the set's add()
and addAll()
methods throw an IllegalArgumentException
. When methods
such as removeAll()
and clear()
are called on the filtered set, only elements
that satisfy the filter will be removed from the underlying set.
The returned set isn't threadsafe or serializable, even if unfiltered
is.
Many of the filtered set's methods, such as size()
, iterate across every element in
the underlying set 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 <B> Set<List<B>> cartesianProduct(List<? extends Set<? extends B>> sets)
Sets.cartesianProduct(ImmutableList.of(
ImmutableSet.of(1, 2),
ImmutableSet.of("A", "B", "C")))
returns a set containing six lists:
ImmutableList.of(1, "A")
ImmutableList.of(1, "B")
ImmutableList.of(1, "C")
ImmutableList.of(2, "A")
ImmutableList.of(2, "B")
ImmutableList.of(2, "C")
The result is guaranteed to be in the "traditional", lexicographical order for Cartesian products that you would get from nesting for loops:
for (B b0 : sets.get(0)) {
for (B b1 : sets.get(1)) {
...
ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
// operate on tuple
}
}
Note that if any input set is empty, the Cartesian product will also be empty. If no sets at all are provided (an empty list), the resulting Cartesian product has one element, an empty list (counterintuitive, but mathematically consistent).
Performance notes: while the cartesian product of sets of size m, n, p
is a
set of size m x n x p
, its actual memory consumption is much smaller. When the
cartesian set is constructed, the input sets are merely copied. Only as the resulting set is
iterated are the individual lists created, and these are not retained after iteration.
B
 any common base class shared by all axes (often just Object
)sets
 the sets to choose elements from, in the order that the elements chosen from those
sets should appear in the resulting listsNullPointerException
 if sets
, any one of the sets
, or any element of a
provided set is nullIllegalArgumentException
 if the cartesian product size exceeds the int
range@SafeVarargs public static <B> Set<List<B>> cartesianProduct(Set<? extends B>... sets)
Sets.cartesianProduct(
ImmutableSet.of(1, 2),
ImmutableSet.of("A", "B", "C"))
returns a set containing six lists:
ImmutableList.of(1, "A")
ImmutableList.of(1, "B")
ImmutableList.of(1, "C")
ImmutableList.of(2, "A")
ImmutableList.of(2, "B")
ImmutableList.of(2, "C")
The result is guaranteed to be in the "traditional", lexicographical order for Cartesian products that you would get from nesting for loops:
for (B b0 : sets.get(0)) {
for (B b1 : sets.get(1)) {
...
ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
// operate on tuple
}
}
Note that if any input set is empty, the Cartesian product will also be empty. If no sets at all are provided (an empty list), the resulting Cartesian product has one element, an empty list (counterintuitive, but mathematically consistent).
Performance notes: while the cartesian product of sets of size m, n, p
is a
set of size m x n x p
, its actual memory consumption is much smaller. When the
cartesian set is constructed, the input sets are merely copied. Only as the resulting set is
iterated are the individual lists created, and these are not retained after iteration.
B
 any common base class shared by all axes (often just Object
)sets
 the sets to choose elements from, in the order that the elements chosen from those
sets should appear in the resulting listsNullPointerException
 if sets
, any one of the sets
, or any element of a
provided set is nullIllegalArgumentException
 if the cartesian product size exceeds the int
range@GwtCompatible(serializable=false) public static <E> Set<Set<E>> powerSet(Set<E> set)
set
. For example, powerSet(ImmutableSet.of(1, 2))
returns the set {{}, {1}, {2}, {1, 2}}
.
Elements appear in these subsets in the same iteration order as they appeared in the input set. The order in which these subsets appear in the outer set is undefined. Note that the power set of the empty set is not the empty set, but a oneelement set containing the empty set.
The returned set and its constituent sets use equals
to decide whether two elements
are identical, even if the input set uses a different concept of equivalence.
Performance notes: while the power set of a set with size n
is of size 2^n
, its memory usage is only O(n)
. When the power set is constructed, the input set
is merely copied. Only as the power set is iterated are the individual subsets created, and
these subsets themselves occupy only a small constant amount of memory.
set
 the set of elements to construct a power set fromIllegalArgumentException
 if set
has more than 30 unique elements (causing the
power set size to exceed the int
range)NullPointerException
 if set
is or contains null
@Beta public static <E> Set<Set<E>> combinations(Set<E> set, int size)
set
of size size
. For example, combinations(ImmutableSet.of(1, 2, 3), 2)
returns the set {{1, 2}, {1, 3}, {2, 3}}
.
Elements appear in these subsets in the same iteration order as they appeared in the input set. The order in which these subsets appear in the outer set is undefined.
The returned set and its constituent sets use equals
to decide whether two elements
are identical, even if the input set uses a different concept of equivalence.
Performance notes: the memory usage of the returned set is only O(n)
. When
the result set is constructed, the input set is merely copied. Only as the result set is
iterated are the individual subsets created. Each of these subsets occupies an additional O(n)
memory but only for as long as the user retains a reference to it. That is, the set returned by
combinations
does not retain the individual subsets.
set
 the set of elements to take combinations ofsize
 the number of elements per combinationsize
elements from set
IllegalArgumentException
 if size
is not between 0 and set.size()
inclusiveNullPointerException
 if set
is or contains null
public static <E> NavigableSet<E> unmodifiableNavigableSet(NavigableSet<E> set)
UnsupportedOperationException
.
The returned navigable set will be serializable if the specified navigable set is serializable.
set
 the navigable set for which an unmodifiable view is to be returned@GwtIncompatible public static <E> NavigableSet<E> synchronizedNavigableSet(NavigableSet<E> navigableSet)
It is imperative that the user manually synchronize on the returned sorted set when
iterating over it or any of its descendingSet
, subSet
, headSet
, or
tailSet
views.
NavigableSet<E> set = synchronizedNavigableSet(new TreeSet<E>());
...
synchronized (set) {
// Must be in the synchronized block
Iterator<E> it = set.iterator();
while (it.hasNext()) {
foo(it.next());
}
}
or:
NavigableSet<E> set = synchronizedNavigableSet(new TreeSet<E>());
NavigableSet<E> set2 = set.descendingSet().headSet(foo);
...
synchronized (set) { // Note: set, not set2!!!
// Must be in the synchronized block
Iterator<E> it = set2.descendingIterator();
while (it.hasNext())
foo(it.next());
}
}
Failure to follow this advice may result in nondeterministic behavior.
The returned navigable set will be serializable if the specified navigable set is serializable.
navigableSet
 the navigable set to be "wrapped" in a synchronized navigable set.@Beta @GwtIncompatible public static <K extends Comparable<? super K>> NavigableSet<K> subSet(NavigableSet<K> set, Range<K> range)
set
whose elements are contained by range
.
This method delegates to the appropriate methods of NavigableSet
(namely subSet()
, tailSet()
, and headSet()
) to actually construct the view. Consult these methods for a full
description of the returned view's behavior.
Warning: Range
s always represent a range of values using the values' natural
ordering. NavigableSet
on the other hand can specify a custom ordering via a Comparator
, which can violate the natural ordering. Using this method (or in general using
Range
) with unnaturallyordered sets can lead to unexpected and undefined behavior.
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