Summary: Ctors | Methods | Inherited Methods | [Expand All]

public class

ConcurrentSkipListSet

extends AbstractSet<E>
implements Serializable Cloneable NavigableSet<E>

java.lang.Object
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractSet<E>
		↳	java.util.concurrent.ConcurrentSkipListSet<E>

Class Overview

A scalable concurrent NavigableSet implementation based on a ConcurrentSkipListMap. The elements of the set are kept sorted according to their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used.

This implementation provides expected average log(n) time cost for the contains, add, and remove operations and their variants. Insertion, removal, and access operations safely execute concurrently by multiple threads. Iterators are weakly consistent, returning elements reflecting the state of the set at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations. Ascending ordered views and their iterators are faster than descending ones.

Beware that, unlike in most collections, the size method is not a constant-time operation. Because of the asynchronous nature of these sets, determining the current number of elements requires a traversal of the elements. Additionally, the bulk operations addAll, removeAll, retainAll, and containsAll are not guaranteed to be performed atomically. For example, an iterator operating concurrently with an addAll operation might view only some of the added elements.

This class and its iterators implement all of the optional methods of the Set and Iterator interfaces. Like most other concurrent collection implementations, this class does not permit the use of null elements, because null arguments and return values cannot be reliably distinguished from the absence of elements.

This class is a member of the Java Collections Framework.

Summary

Public Constructors
	ConcurrentSkipListSet() Constructs a new, empty set that orders its elements according to their `natural ordering`.
	ConcurrentSkipListSet(Comparator<? super E> comparator) Constructs a new, empty set that orders its elements according to the specified comparator.
	ConcurrentSkipListSet(Collection<? extends E> c) Constructs a new set containing the elements in the specified collection, that orders its elements according to their `natural ordering`.
	ConcurrentSkipListSet(SortedSet<E> s) Constructs a new set containing the same elements and using the same ordering as the specified sorted set.

Public Methods
boolean	add(E e) Adds the specified element to this set if it is not already present.
E	ceiling(E e) Returns the smallest element bigger than or equal to the specified one, or null if no such element.
void	clear() Removes all of the elements from this set.
ConcurrentSkipListSet<E>	clone() Returns a shallow copy of this `ConcurrentSkipListSet` instance.
Comparator<? super E>	comparator() Returns the comparator used to compare elements in this `SortedSet`.
boolean	contains(Object o) Returns `true` if this set contains the specified element.
Iterator<E>	descendingIterator() Returns an iterator over the elements in this set in descending order.
NavigableSet<E>	descendingSet() Returns a reverse order view of the elements contained in this set.
boolean	equals(Object o) Compares the specified object with this set for equality.
E	first() Returns the first element in this `SortedSet`.
E	floor(E e) Returns the biggest element less than or equal to the specified one, or null if no such element.
NavigableSet<E>	headSet(E toElement) Returns a `SortedSet` of the specified portion of this `SortedSet` which contains elements less than the end element.
NavigableSet<E>	headSet(E toElement, boolean inclusive) Returns a NavigableSet of the specified portion of this set which contains elements less than (or equal to, depends on endInclusive) the end element.
E	higher(E e) Returns the smallest element bigger than the specified one, or null if no such element.
boolean	isEmpty() Returns `true` if this set contains no elements.
Iterator<E>	iterator() Returns an iterator over the elements in this set in ascending order.
E	last() Returns the last element in this `SortedSet`.
E	lower(E e) Returns the biggest element less than the specified one, or null if no such element.
E	pollFirst() Deletes and returns the smallest element, or null if the set is empty.
E	pollLast() Deletes and returns the biggest element, or null if the set is empty.
boolean	remove(Object o) Removes the specified element from this set if it is present.
boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection.
int	size() Returns the number of elements in this set.
NavigableSet<E>	subSet(E fromElement, E toElement) Returns a `SortedSet` of the specified portion of this `SortedSet` which contains elements greater or equal to the start element but less than the end element.
NavigableSet<E>	subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element but less than (or equal to, depends on endInclusive) the end element.
NavigableSet<E>	tailSet(E fromElement, boolean inclusive) Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element.
NavigableSet<E>	tailSet(E fromElement) Returns a `SortedSet` of the specified portion of this `SortedSet` which contains elements greater or equal to the start element.

[Expand]

Inherited Methods

From class java.util.AbstractSet

From class java.util.AbstractCollection

boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `collection` to the contents of this `Collection` (optional).
void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this `Collection`.
Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.
String	toString() Returns the string representation of this `Collection`.

From class java.lang.Object

Object	clone() Creates and returns a copy of this `Object`.
boolean	equals(Object o) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Called before the object's memory is reclaimed by the VM.
final Class<? extends Object>	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() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object.
final void	wait(long millis, 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 millis) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.

From interface java.lang.Iterable

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `Collection` to the contents of this `Collection` (optional).
abstract void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
abstract boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
abstract boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `Collection`.
abstract Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.

From interface java.util.NavigableSet

abstract E	ceiling(E e) Returns the smallest element bigger than or equal to the specified one, or null if no such element.
abstract Iterator<E>	descendingIterator() Returns a descending iterator of this set.
abstract NavigableSet<E>	descendingSet() Returns a reverse order view of this set.
abstract E	floor(E e) Returns the biggest element less than or equal to the specified one, or null if no such element.
abstract NavigableSet<E>	headSet(E end, boolean endInclusive) Returns a NavigableSet of the specified portion of this set which contains elements less than (or equal to, depends on endInclusive) the end element.
abstract E	higher(E e) Returns the smallest element bigger than the specified one, or null if no such element.
abstract E	lower(E e) Returns the biggest element less than the specified one, or null if no such element.
abstract E	pollFirst() Deletes and returns the smallest element, or null if the set is empty.
abstract E	pollLast() Deletes and returns the biggest element, or null if the set is empty.
abstract NavigableSet<E>	subSet(E start, boolean startInclusive, E end, boolean endInclusive) Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element but less than (or equal to, depends on endInclusive) the end element.
abstract NavigableSet<E>	tailSet(E start, boolean startInclusive) Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element.

From interface java.util.Set

abstract boolean	add(E object) Adds the specified object to this set.
abstract boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified collection which do not exist yet in this set.
abstract void	clear() Removes all elements from this set, leaving it empty.
abstract boolean	contains(Object object) Searches this set for the specified object.
abstract boolean	containsAll(Collection<?> collection) Searches this set for all objects in the specified collection.
abstract boolean	equals(Object object) Compares the specified object to this set, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns the hash code for this set.
abstract boolean	isEmpty() Returns true if this set has no elements.
abstract Iterator<E>	iterator() Returns an iterator on the elements of this set.
abstract boolean	remove(Object object) Removes the specified object from this set.
abstract boolean	removeAll(Collection<?> collection) Removes all objects in the specified collection from this set.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this set that are not contained in the specified collection.
abstract int	size() Returns the number of elements in this set.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this set.
abstract Object[]	toArray() Returns an array containing all elements contained in this set.

From interface java.util.SortedSet

Public Constructors

public ConcurrentSkipListSet ()

Since: API Level 9

Constructs a new, empty set that orders its elements according to their natural ordering.

public ConcurrentSkipListSet (Comparator<? super E> comparator)

Since: API Level 9

Constructs a new, empty set that orders its elements according to the specified comparator.

Parameters

comparator	the comparator that will be used to order this set. If `null`, the `natural ordering` of the elements will be used.

public ConcurrentSkipListSet (Collection<? extends E> c)

Since: API Level 9

Constructs a new set containing the elements in the specified collection, that orders its elements according to their natural ordering.

Parameters

c	The elements that will comprise the new set

Throws

ClassCastException	if the elements in `c` are not `Comparable`, or are not mutually comparable
NullPointerException	if the specified collection or any of its elements are null

public ConcurrentSkipListSet (SortedSet<E> s)

Since: API Level 9

Constructs a new set containing the same elements and using the same ordering as the specified sorted set.

Parameters

s	sorted set whose elements will comprise the new set

Throws

NullPointerException	if the specified sorted set or any of its elements are null

Public Methods

public boolean add (E e)

Since: API Level 9

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if the set contains no element e2 such that e.equals(e2). If this set already contains the element, the call leaves the set unchanged and returns false.

Parameters

e	element to be added to this set

Returns

true if this set did not already contain the specified element

Throws

ClassCastException	if `e` cannot be compared with the elements currently in this set
NullPointerException	if the specified element is null

public E ceiling (E e)

Since: API Level 9

Returns the smallest element bigger than or equal to the specified one, or null if no such element.

Parameters

e	the specified element

Returns

the smallest element bigger than or equal to the specified one, or null if no such element

Throws

ClassCastException
NullPointerException	if the specified element is null

public void clear ()

Since: API Level 9

Removes all of the elements from this set.

public ConcurrentSkipListSet<E> clone ()

Since: API Level 9

Returns a shallow copy of this ConcurrentSkipListSet instance. (The elements themselves are not cloned.)

Returns

a shallow copy of this set

public Comparator<? super E> comparator ()

Since: API Level 9

Returns the comparator used to compare elements in this SortedSet.

Returns

a comparator or null if the natural ordering is used.

public boolean contains (Object o)

Since: API Level 9

Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that o.equals(e).

Parameters

o	object to be checked for containment in this set

Returns

true if this set contains the specified element

Throws

ClassCastException	if the specified element cannot be compared with the elements currently in this set
NullPointerException	if the specified element is null

public Iterator<E> descendingIterator ()

Since: API Level 9

Returns an iterator over the elements in this set in descending order.

Returns

an iterator over the elements in this set in descending order

public NavigableSet<E> descendingSet ()

Since: API Level 9

Returns a reverse order view of the elements contained in this set. The descending set is backed by this set, so changes to the set are reflected in the descending set, and vice-versa.

The returned set has an ordering equivalent to Collections.reverseOrder(comparator()). The expression s.descendingSet().descendingSet() returns a view of s essentially equivalent to s.

Returns

a reverse order view of this set

public boolean equals (Object o)

Since: API Level 9

Compares the specified object with this set for equality. Returns true if the specified object is also a set, the two sets have the same size, and every member of the specified set is contained in this set (or equivalently, every member of this set is contained in the specified set). This definition ensures that the equals method works properly across different implementations of the set interface.

Parameters

o	the object to be compared for equality with this set

Returns

true if the specified object is equal to this set

public E first ()

Since: API Level 9

Returns the first element in this SortedSet. The first element is the lowest element.

Returns

the first element.

Throws

NoSuchElementException

public E floor (E e)

Since: API Level 9

Returns the biggest element less than or equal to the specified one, or null if no such element.

Parameters

e	the specified element

Returns

the biggest element less than or equal to the specified one, or null if no such element

Throws

ClassCastException
NullPointerException	if the specified element is null

public NavigableSet<E> headSet (E toElement)

Since: API Level 9

Returns a SortedSet of the specified portion of this SortedSet which contains elements less than the end element. The returned SortedSet is backed by this SortedSet so changes to one set are reflected by the other.

Parameters

toElement	the end element.

Returns

a subset where the elements are less than end.

Throws

ClassCastException
NullPointerException	if `toElement` is null
IllegalArgumentException

public NavigableSet<E> headSet (E toElement, boolean inclusive)

Since: API Level 9

Returns a NavigableSet of the specified portion of this set which contains elements less than (or equal to, depends on endInclusive) the end element. The returned NavigableSet is backed by this set so changes to one are reflected by the other.

Parameters

toElement	the end element
inclusive	true if the end element is in the returned set

Returns

the subset

Throws

ClassCastException
NullPointerException	if `toElement` is null
IllegalArgumentException

public E higher (E e)

Since: API Level 9

Returns the smallest element bigger than the specified one, or null if no such element.

Parameters

e	the specified element

Returns

the smallest element bigger than the specified one, or null if no such element

Throws

ClassCastException
NullPointerException	if the specified element is null

public boolean isEmpty ()

Since: API Level 9

Returns true if this set contains no elements.

Returns

true if this set contains no elements

public Iterator<E> iterator ()

Since: API Level 9

Returns an iterator over the elements in this set in ascending order.

Returns

an iterator over the elements in this set in ascending order

public E last ()

Since: API Level 9

Returns the last element in this SortedSet. The last element is the highest element.

Returns

the last element.

Throws

NoSuchElementException

public E lower (E e)

Since: API Level 9

Returns the biggest element less than the specified one, or null if no such element.

Parameters

e	the specified element

Returns

the biggest element less than the specified one, or null if no such element

Throws

ClassCastException
NullPointerException	if the specified element is null

public E pollFirst ()

Since: API Level 9

Deletes and returns the smallest element, or null if the set is empty.

Returns

the smallest element, or null if the set is empty

public E pollLast ()

Since: API Level 9

Deletes and returns the biggest element, or null if the set is empty.

Returns

the biggest element, or null if the set is empty

public boolean remove (Object o)

Since: API Level 9

Removes the specified element from this set if it is present. More formally, removes an element e such that o.equals(e), if this set contains such an element. Returns true if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.)

Parameters

o	object to be removed from this set, if present

Returns

true if this set contained the specified element

Throws

ClassCastException	if `o` cannot be compared with the elements currently in this set
NullPointerException	if the specified element is null

public boolean removeAll (Collection<?> c)

Since: API Level 9

Removes from this set all of its elements that are contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.

Parameters

c	collection containing elements to be removed from this set

Returns

true if this set changed as a result of the call

Throws

ClassCastException	if the types of one or more elements in this set are incompatible with the specified collection
NullPointerException	if the specified collection or any of its elements are null

public int size ()

Since: API Level 9

Returns the number of elements in this set. If this set contains more than Integer.MAX_VALUE elements, it returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these sets, determining the current number of elements requires traversing them all to count them. Additionally, it is possible for the size to change during execution of this method, in which case the returned result will be inaccurate. Thus, this method is typically not very useful in concurrent applications.

Returns

the number of elements in this set

public NavigableSet<E> subSet (E fromElement, E toElement)

Since: API Level 9

Returns a SortedSet of the specified portion of this SortedSet which contains elements greater or equal to the start element but less than the end element. The returned SortedSet is backed by this SortedMap so changes to one set are reflected by the other.

Parameters

fromElement	the start element.
toElement	the end element.

Returns

a subset where the elements are greater or equal to start and less than end.

Throws

ClassCastException
NullPointerException	if `fromElement` or `toElement` is null
IllegalArgumentException

public NavigableSet<E> subSet (E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)

Since: API Level 9

Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element but less than (or equal to, depends on endInclusive) the end element. The returned NavigableSet is backed by this set so changes to one are reflected by the other.

Parameters

fromElement	the start element
fromInclusive	true if the start element is in the returned set
toElement	the end element
toInclusive	true if the end element is in the returned set

Returns

the subset

Throws

ClassCastException
NullPointerException	if `fromElement` or `toElement` is null
IllegalArgumentException

public NavigableSet<E> tailSet (E fromElement, boolean inclusive)

Since: API Level 9

Returns a NavigableSet of the specified portion of this set which contains elements greater (or equal to, depends on startInclusive) the start element. The returned NavigableSet is backed by this set so changes to one are reflected by the other.

Parameters

fromElement	the start element
inclusive	true if the start element is in the returned set

Returns

the subset

Throws

ClassCastException
NullPointerException	if `fromElement` is null
IllegalArgumentException

public NavigableSet<E> tailSet (E fromElement)

Since: API Level 9

Returns a SortedSet of the specified portion of this SortedSet which contains elements greater or equal to the start element. The returned SortedSet is backed by this SortedSet so changes to one set are reflected by the other.

Parameters

fromElement	the start element.

Returns

a subset where the elements are greater or equal to start .

Throws

ClassCastException
NullPointerException	if `fromElement` is null
IllegalArgumentException

Interfaces

Classes

Enums

Exceptions

ConcurrentSkipListSet

Class Overview

Summary

Public Constructors

public ConcurrentSkipListSet ()

public ConcurrentSkipListSet (Comparator<? super E> comparator)

Parameters

public ConcurrentSkipListSet (Collection<? extends E> c)

Parameters

Throws

public ConcurrentSkipListSet (SortedSet<E> s)

Parameters

Throws

Public Methods

public boolean add (E e)

Parameters

Returns

Throws

public E ceiling (E e)

Parameters

Returns

Throws

public void clear ()

public ConcurrentSkipListSet<E> clone ()

Returns

public Comparator<? super E> comparator ()

Returns

public boolean contains (Object o)

Parameters

Returns

Throws

public Iterator<E> descendingIterator ()

Returns

public NavigableSet<E> descendingSet ()

Returns

public boolean equals (Object o)

Parameters

Returns

public E first ()

Returns

Throws

public E floor (E e)

Parameters

Returns

Throws

public NavigableSet<E> headSet (E toElement)

Parameters

Returns

Throws

public NavigableSet<E> headSet (E toElement, boolean inclusive)

Parameters

Returns

Throws

public E higher (E e)

Parameters

Returns

Throws

public boolean isEmpty ()

Returns

public Iterator<E> iterator ()

Returns

public E last ()

Returns

Throws

public E lower (E e)

Parameters

Returns

Throws

public E pollFirst ()

Returns

public E pollLast ()

Returns

public boolean remove (Object o)

Parameters

Returns

Throws