EnumSet

public abstract class EnumSet extends AbstractSet<E extends Enum<E>>
implements Cloneable Serializable

A specialized Set implementation for use with enum types. All of the elements in an enum set must come from a single enum type that is specified, explicitly or implicitly, when the set is created. Enum sets are represented internally as bit vectors. This representation is extremely compact and efficient. The space and time performance of this class should be good enough to allow its use as a high-quality, typesafe alternative to traditional int-based "bit flags." Even bulk operations (such as containsAll and retainAll) should run very quickly if their argument is also an enum set.

The iterator returned by the iterator method traverses the elements in their natural order (the order in which the enum constants are declared). The returned iterator is weakly consistent: it will never throw ConcurrentModificationException and it may or may not show the effects of any modifications to the set that occur while the iteration is in progress.

Null elements are not permitted. Attempts to insert a null element will throw NullPointerException. Attempts to test for the presence of a null element or to remove one will, however, function properly.

Like most collection implementations, EnumSet is not synchronized. If multiple threads access an enum set concurrently, and at least one of the threads modifies the set, it should be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the enum set. If no such object exists, the set should be "wrapped" using the Collections.synchronizedSet(Set) method. This is best done at creation time, to prevent accidental unsynchronized access:

 Set<MyEnum> s = Collections.synchronizedSet(EnumSet.noneOf(MyEnum.class));
 

Implementation note: All basic operations execute in constant time. They are likely (though not guaranteed) to be much faster than their HashSet counterparts. Even bulk operations execute in constant time if their argument is also an enum set.

This class is a member of the Java Collections Framework.

See Also

• EnumMap

Public Method Summary

static <E extends Enum<E>> EnumSet<E>	allOf(Class<E> elementType) Creates an enum set containing all of the elements in the specified element type.
EnumSet<E>	clone() Returns a copy of this set.
static <E extends Enum<E>> EnumSet<E>	complementOf(EnumSet<E> s) Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.
static <E extends Enum<E>> EnumSet<E>	copyOf(EnumSet<E> s) Creates an enum set with the same element type as the specified enum set, initially containing the same elements (if any).
static <E extends Enum<E>> EnumSet<E>	copyOf(Collection<E> c) Creates an enum set initialized from the specified collection.
static <E extends Enum<E>> EnumSet<E>	noneOf(Class<E> elementType) Creates an empty enum set with the specified element type.
static <E extends Enum<E>> EnumSet<E>	of(E first, E... rest) Creates an enum set initially containing the specified elements.
static <E extends Enum<E>> EnumSet<E>	of(E e1, E e2, E e3) Creates an enum set initially containing the specified elements.
static <E extends Enum<E>> EnumSet<E>	of(E e1, E e2) Creates an enum set initially containing the specified elements.
static <E extends Enum<E>> EnumSet<E>	of(E e1, E e2, E e3, E e4, E e5) Creates an enum set initially containing the specified elements.
static <E extends Enum<E>> EnumSet<E>	of(E e1, E e2, E e3, E e4) Creates an enum set initially containing the specified elements.
static <E extends Enum<E>> EnumSet<E>	of(E e) Creates an enum set initially containing the specified element.
static <E extends Enum<E>> EnumSet<E>	range(E from, E to) Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints.

Inherited Method Summary

From class java.util.AbstractSet

boolean	equals(Object o) Compares the specified object with this set for equality.
int	hashCode() Returns the hash code value for this set.
boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).

From class java.util.AbstractCollection

boolean	add(E e) Ensures that this collection contains the specified element (optional operation). This implementation always throws an UnsupportedOperationException.
boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation). This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn.
void	clear() Removes all of the elements from this collection (optional operation). This implementation iterates over this collection, removing each element using the Iterator.remove operation.
boolean	contains(Object o) Returns true if this collection contains the specified element. This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection. This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection.
boolean	isEmpty() Returns true if this collection contains no elements. This implementation returns size() == 0.
abstract Iterator<E>	iterator() Returns an iterator over the elements contained in this collection.
boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation). This implementation iterates over the collection looking for the specified element.
boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
abstract int	size() Returns the number of elements in this collection.
<T> T[]	toArray(T[] contents) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index 0.
Object[]	toArray() Returns an array containing all of the elements in this collection. This implementation returns an array containing all the elements returned by this collection's iterator, in the same order, stored in consecutive elements of the array, starting with index 0.
String	toString() Returns a string representation of this collection.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.util.Set

abstract boolean	add(E e) Adds the specified element to this set if it is not already present (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this set if they're not already present (optional operation).
abstract void	clear() Removes all of the elements from this set (optional operation).
abstract boolean	contains(Object o) Returns true if this set contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this set contains all of the elements of the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this set for equality.
abstract int	hashCode() Returns the hash code value for this set.
abstract boolean	isEmpty() Returns true if this set contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this set.
abstract boolean	remove(Object o) Removes the specified element from this set if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this set that are contained in the specified collection (optional operation).
abstract int	size() Returns the number of elements in this set (its cardinality).
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this set.
abstract <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.
abstract Object[]	toArray() Returns an array containing all of the elements in this set.

From interface java.util.Collection

abstract boolean	add(E e) Ensures that this collection contains the specified element (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation).
abstract void	clear() Removes all of the elements from this collection (optional operation).
abstract boolean	contains(Object o) Returns true if this collection contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this collection for equality.
abstract int	hashCode() Returns the hash code value for this collection.
abstract boolean	isEmpty() Returns true if this collection contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this collection.
Stream<E>	parallelStream() Returns a possibly parallel Stream with this collection as its source.
abstract boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	removeIf(Predicate<? super E> filter) Removes all of the elements of this collection that satisfy the given predicate.
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
abstract int	size() Returns the number of elements in this collection.
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this collection.
Stream<E>	stream() Returns a sequential Stream with this collection as its source.
abstract <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
abstract Object[]	toArray() Returns an array containing all of the elements in this collection.

From interface java.lang.Iterable

void	forEach(Consumer<? super T> action) Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
abstract Iterator<E extends Enum<E>>	iterator() Returns an iterator over elements of type T.
Spliterator<E extends Enum<E>>	spliterator() Creates a Spliterator over the elements described by this Iterable.

Public Methods

public static EnumSet<E> allOf (Class<E> elementType)

Creates an enum set containing all of the elements in the specified element type.

Parameters

elementType	the class object of the element type for this enum set

Returns

• An enum set containing all the elements in the specified type.

Throws

NullPointerException	if elementType is null

public EnumSet<E> clone ()

Returns a copy of this set.

Returns

• a copy of this set

public static EnumSet<E> complementOf (EnumSet<E> s)

Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.

Parameters

s	the enum set from whose complement to initialize this enum set

Returns

• The complement of the specified set in this set

Throws

NullPointerException	if s is null

public static EnumSet<E> copyOf (EnumSet<E> s)

Creates an enum set with the same element type as the specified enum set, initially containing the same elements (if any).

Parameters

s	the enum set from which to initialize this enum set

Returns

• A copy of the specified enum set.

Throws

NullPointerException	if s is null

public static EnumSet<E> copyOf (Collection<E> c)

Creates an enum set initialized from the specified collection. If the specified collection is an EnumSet instance, this static factory method behaves identically to copyOf(EnumSet). Otherwise, the specified collection must contain at least one element (in order to determine the new enum set's element type).

Parameters

c	the collection from which to initialize this enum set

Returns

• An enum set initialized from the given collection.

Throws

IllegalArgumentException	if c is not an EnumSet instance and contains no elements
NullPointerException	if c is null

public static EnumSet<E> noneOf (Class<E> elementType)

Creates an empty enum set with the specified element type.

Parameters

elementType	the class object of the element type for this enum set

Returns

• An empty enum set of the specified type.

Throws

NullPointerException	if elementType is null

public static EnumSet<E> of (E first, E... rest)

Creates an enum set initially containing the specified elements. This factory, whose parameter list uses the varargs feature, may be used to create an enum set initially containing an arbitrary number of elements, but it is likely to run slower than the overloadings that do not use varargs.

Parameters

first	an element that the set is to contain initially
rest	the remaining elements the set is to contain initially

Returns

• an enum set initially containing the specified elements

Throws

NullPointerException	if any of the specified elements are null, or if rest is null

public static EnumSet<E> of (E e1, E e2, E e3)

Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.

Parameters

e1	an element that this set is to contain initially
e2	another element that this set is to contain initially
e3	another element that this set is to contain initially

Returns

• an enum set initially containing the specified elements

Throws

NullPointerException	if any parameters are null

public static EnumSet<E> of (E e1, E e2)

Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.

Parameters

e1	an element that this set is to contain initially
e2	another element that this set is to contain initially

Returns

• an enum set initially containing the specified elements

Throws

NullPointerException	if any parameters are null

public static EnumSet<E> of (E e1, E e2, E e3, E e4, E e5)

Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.

Parameters

e1	an element that this set is to contain initially
e2	another element that this set is to contain initially
e3	another element that this set is to contain initially
e4	another element that this set is to contain initially
e5	another element that this set is to contain initially

Returns

• an enum set initially containing the specified elements

Throws

NullPointerException	if any parameters are null

public static EnumSet<E> of (E e1, E e2, E e3, E e4)

Creates an enum set initially containing the specified elements. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.

Parameters

e1	an element that this set is to contain initially
e2	another element that this set is to contain initially
e3	another element that this set is to contain initially
e4	another element that this set is to contain initially

Returns

• an enum set initially containing the specified elements

Throws

NullPointerException	if any parameters are null

public static EnumSet<E> of (E e)

Creates an enum set initially containing the specified element. Overloadings of this method exist to initialize an enum set with one through five elements. A sixth overloading is provided that uses the varargs feature. This overloading may be used to create an enum set initially containing an arbitrary number of elements, but is likely to run slower than the overloadings that do not use varargs.

Parameters

e	the element that this set is to contain initially

Returns

• an enum set initially containing the specified element

Throws

NullPointerException	if e is null

public static EnumSet<E> range (E from, E to)

Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints. The returned set will contain the endpoints themselves, which may be identical but must not be out of order.

Parameters

from	the first element in the range
to	the last element in the range

Returns

• an enum set initially containing all of the elements in the range defined by the two specified endpoints

Throws

NullPointerException	if from or to are null
IllegalArgumentException	if from.compareTo(to) > 0