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Added in API level 9

ConcurrentSkipListSet

public class ConcurrentSkipListSet
extends AbstractSet<E> implements NavigableSet<E>, Cloneable, Serializable

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


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, and so may report inaccurate results if this collection is modified during traversal. Additionally, the bulk operations addAll, removeAll, retainAll, containsAll, equals, and toArray 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.

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 least element in this set greater than or equal to the given element, or null if there is 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 greatest element in this set less than or equal to the given element, or null if there is 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.

Equivalent to headSet(toElement, false).

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

Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.

E higher(E e)

Returns the least element in this set strictly greater than the given element, or null if there is 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 greatest element in this set strictly less than the given element, or null if there is no such element.

E pollFirst()

Retrieves and removes the first (lowest) element, or returns null if this set is empty.

E pollLast()

Retrieves and removes the last (highest) element, or returns null if this 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.

Equivalent to subSet(fromElement, true, toElement, false).

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

Returns a view of the portion of this set whose elements range from fromElement to toElement.

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

Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

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.

Equivalent to tailSet(fromElement, true).

Inherited methods

From class java.util.AbstractSet
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.Set
From interface java.util.Collection
From interface java.util.NavigableSet
From interface java.lang.Iterable
From interface java.util.SortedSet

Public constructors

ConcurrentSkipListSet

Added in API level 9
ConcurrentSkipListSet ()

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

ConcurrentSkipListSet

Added in API level 9
ConcurrentSkipListSet (Comparator<? super E> comparator)

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

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

ConcurrentSkipListSet

Added in API level 9
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.

Parameters
c Collection: 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

ConcurrentSkipListSet

Added in API level 9
ConcurrentSkipListSet (SortedSet<E> s)

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

Parameters
s SortedSet: 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

add

Added in API level 9
boolean add (E e)

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 E: element to be added to this set
Returns
boolean 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

ceiling

Added in API level 9
E ceiling (E e)

Returns the least element in this set greater than or equal to the given element, or null if there is no such element.

Parameters
e E: the value to match
Returns
E the least element greater than or equal to e, or null if there is no such element
Throws
ClassCastException
NullPointerException if the specified element is null

clear

Added in API level 9
void clear ()

Removes all of the elements from this set.

clone

Added in API level 9
ConcurrentSkipListSet<E> clone ()

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

Returns
ConcurrentSkipListSet<E> a shallow copy of this set

comparator

Added in API level 9
Comparator<? super E> comparator ()

Returns the comparator used to compare elements in this SortedSet.

Returns
Comparator<? super E> a comparator or null if the natural ordering is used.

contains

Added in API level 9
boolean contains (Object o)

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: object to be checked for containment in this set
Returns
boolean 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

descendingIterator

Added in API level 9
Iterator<E> descendingIterator ()

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

Returns
Iterator<E> an iterator over the elements in this set in descending order

descendingSet

Added in API level 9
NavigableSet<E> descendingSet ()

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
NavigableSet<E> a reverse order view of this set

equals

Added in API level 9
boolean equals (Object o)

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 Object: the object to be compared for equality with this set
Returns
boolean true if the specified object is equal to this set

first

Added in API level 9
E first ()

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

Returns
E the first element.
Throws
NoSuchElementException

floor

Added in API level 9
E floor (E e)

Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.

Parameters
e E: the value to match
Returns
E the greatest element less than or equal to e, or null if there is no such element
Throws
ClassCastException
NullPointerException if the specified element is null

headSet

Added in API level 9
NavigableSet<E> headSet (E toElement)

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.

Equivalent to headSet(toElement, false).

Parameters
toElement E: the end element.
Returns
NavigableSet<E> a subset where the elements are less than end.
Throws
ClassCastException
NullPointerException if toElement is null
IllegalArgumentException

headSet

Added in API level 9
NavigableSet<E> headSet (E toElement, 
                boolean inclusive)

Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement. The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
toElement E: high endpoint of the returned set
inclusive boolean: true if the high endpoint is to be included in the returned view
Returns
NavigableSet<E> a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement
Throws
ClassCastException
NullPointerException if toElement is null
IllegalArgumentException

higher

Added in API level 9
E higher (E e)

Returns the least element in this set strictly greater than the given element, or null if there is no such element.

Parameters
e E: the value to match
Returns
E the least element greater than e, or null if there is no such element
Throws
ClassCastException
NullPointerException if the specified element is null

isEmpty

Added in API level 9
boolean isEmpty ()

Returns true if this set contains no elements.

Returns
boolean true if this set contains no elements

iterator

Added in API level 9
Iterator<E> iterator ()

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

Returns
Iterator<E> an iterator over the elements in this set in ascending order

last

Added in API level 9
E last ()

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

Returns
E the last element.
Throws
NoSuchElementException

lower

Added in API level 9
E lower (E e)

Returns the greatest element in this set strictly less than the given element, or null if there is no such element.

Parameters
e E: the value to match
Returns
E the greatest element less than e, or null if there is no such element
Throws
ClassCastException
NullPointerException if the specified element is null

pollFirst

Added in API level 9
E pollFirst ()

Retrieves and removes the first (lowest) element, or returns null if this set is empty.

Returns
E the first element, or null if this set is empty

pollLast

Added in API level 9
E pollLast ()

Retrieves and removes the last (highest) element, or returns null if this set is empty.

Returns
E the last element, or null if this set is empty

remove

Added in API level 9
boolean remove (Object o)

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: object to be removed from this set, if present
Returns
boolean 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

removeAll

Added in API level 9
boolean removeAll (Collection<?> c)

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: collection containing elements to be removed from this set
Returns
boolean 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

size

Added in API level 9
int size ()

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
int the number of elements in this set

subSet

Added in API level 9
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. The returned SortedSet is backed by this SortedMap so changes to one set are reflected by the other.

Equivalent to subSet(fromElement, true, toElement, false).

Parameters
fromElement E: the start element.
toElement E: the end element.
Returns
NavigableSet<E> 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

subSet

Added in API level 9
NavigableSet<E> subSet (E fromElement, 
                boolean fromInclusive, 
                E toElement, 
                boolean toInclusive)

Returns a view of the portion of this set whose elements range from fromElement to toElement. If fromElement and toElement are equal, the returned set is empty unless fromExclusive and toExclusive are both true. The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
fromElement E: low endpoint of the returned set
fromInclusive boolean: true if the low endpoint is to be included in the returned view
toElement E: high endpoint of the returned set
toInclusive boolean: true if the high endpoint is to be included in the returned view
Returns
NavigableSet<E> a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive
Throws
ClassCastException
NullPointerException if fromElement or toElement is null
IllegalArgumentException

tailSet

Added in API level 9
NavigableSet<E> tailSet (E fromElement, 
                boolean inclusive)

Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement. The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
fromElement E: low endpoint of the returned set
inclusive boolean: true if the low endpoint is to be included in the returned view
Returns
NavigableSet<E> a view of the portion of this set whose elements are greater than or equal to fromElement
Throws
ClassCastException
NullPointerException if fromElement is null
IllegalArgumentException

tailSet

Added in API level 9
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. The returned SortedSet is backed by this SortedSet so changes to one set are reflected by the other.

Equivalent to tailSet(fromElement, true).

Parameters
fromElement E: the start element.
Returns
NavigableSet<E> a subset where the elements are greater or equal to start .
Throws
ClassCastException
NullPointerException if fromElement is null
IllegalArgumentException
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