java.util.concurrent
class ConcurrentSkipListSet

java.lang.Object java.util.AbstractCollection java.util.AbstractSet java.util.concurrent.ConcurrentSkipListSet

All Implemented Interfaces:

Serializable, Cloneable, Collection, NavigableSet, Set

Most common way to construct:

ConcurrentSkipListSet q = new ConcurrentSkipListSet();

Based on 47 examples

public class ConcurrentSkipListSet
extends AbstractSet
implements NavigableSet, Cloneable, Serializable

A scalable concurrent {@link NavigableSet} implementation based on a {@link ConcurrentSkipListMap}. The elements of the set are kept sorted according to their {@linkplain Comparable natural ordering}, or by a {@link 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 {@link 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 {@link Set} and {@link 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.

ConcurrentSkipListSet

public ConcurrentSkipListSet()

Constructs a new, empty set that orders its elements according to their {@linkplain Comparable natural ordering}.

ConcurrentSkipListSet

public ConcurrentSkipListSet(Collection c)

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

Parameters:

c - The elements that will comprise the new set

ConcurrentSkipListSet

public ConcurrentSkipListSet(Comparator comparator)

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 {@linkplain Comparable natural ordering} of the elements will be used.

ConcurrentSkipListSet

public ConcurrentSkipListSet(SortedSet s)

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

add

public boolean add(Object 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.

Overrides:

add in class AbstractCollection

Parameters:

e - element to be added to this set

Returns:

true if this set did not already contain the specified element

ceiling

public Object ceiling(Object e)

Parameters:

e

clear

public void clear()

Removes all of the elements from this set.

Overrides:

clear in class AbstractCollection

clone

public ConcurrentSkipListSet clone()

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

Overrides:

clone in class Object

Returns:

a shallow copy of this set

comparator

public Comparator comparator()

contains

public 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).

Overrides:

contains in class AbstractCollection

Parameters:

o - object to be checked for containment in this set

Returns:

true if this set contains the specified element

descendingIterator

public Iterator descendingIterator()

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

Returns:

an iterator over the elements in this set in descending order

descendingSet

public NavigableSet 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 {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator()). The expression {@code s.descendingSet().descendingSet()} returns a view of {@code s} essentially equivalent to {@code s}.

Returns:

a reverse order view of this set

equals

public 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.

Overrides:

equals in class AbstractSet

Parameters:

o - the object to be compared for equality with this set

Returns:

true if the specified object is equal to this set

first

public Object first()

floor

public Object floor(Object e)

Parameters:

e

headSet

public NavigableSet headSet(Object toElement)

Parameters:

toElement

headSet

public NavigableSet headSet(Object toElement,
                            boolean inclusive)

Parameters:

toElement

inclusive

higher

public Object higher(Object e)

Parameters:

e

isEmpty

public boolean isEmpty()

Returns true if this set contains no elements.

Overrides:

isEmpty in class AbstractCollection

Returns:

true if this set contains no elements

iterator

public Iterator iterator()

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

Overrides:

iterator in class AbstractCollection

Returns:

an iterator over the elements in this set in ascending order

last

public Object last()

lower

public Object lower(Object e)

Parameters:

e

pollFirst

public Object pollFirst()

pollLast

public Object pollLast()

remove

public 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.)

Overrides:

remove in class AbstractCollection

Parameters:

o - object to be removed from this set, if present

Returns:

true if this set contained the specified element

removeAll

public 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.

Overrides:

removeAll in class AbstractSet

Parameters:

c - collection containing elements to be removed from this set

Returns:

true if this set changed as a result of the call

size

public 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.

Overrides:

size in class AbstractCollection

Returns:

the number of elements in this set

subSet

public NavigableSet subSet(Object fromElement,
                           boolean fromInclusive,
                           Object toElement,
                           boolean toInclusive)

Parameters:

fromElement

fromInclusive

toElement

toInclusive

subSet

public NavigableSet subSet(Object fromElement,
                           Object toElement)

Parameters:

fromElement

toElement

tailSet

public NavigableSet tailSet(Object fromElement)

Parameters:

fromElement

tailSet

public NavigableSet tailSet(Object fromElement,
                            boolean inclusive)

Parameters:

fromElement

inclusive