Class ConcurrentSkipListSet<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.AbstractSet<E>
-
- java.util.concurrent.ConcurrentSkipListSet<E>
- Type Parameters:
-
E
- the type of elements maintained by this set
- All Implemented Interfaces:
-
Serializable
,Cloneable
,Iterable<E>
,Collection<E>
,NavigableSet<E>
,Set<E>
,SortedSet<E>
public class ConcurrentSkipListSet<E> extends AbstractSet<E> implements NavigableSet<E>, Cloneable, Serializable
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 and spliterators are weakly consistent.
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.
Bulk operations that add, remove, or examine multiple elements, such as AbstractCollection.addAll(java.util.Collection<? extends E>)
, Collection.removeIf(java.util.function.Predicate<? super E>)
or Iterable.forEach(java.util.function.Consumer<? super T>)
, are not guaranteed to be performed atomically. For example, a forEach
traversal concurrent with an
addAll
operation might observe 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.
- Since:
- 1.6
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
ConcurrentSkipListSet() | Constructs a new, empty set that orders its elements according to their natural ordering. |
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(Comparator<? super E> comparator) | Constructs a new, empty set that orders its elements according to the specified comparator. |
ConcurrentSkipListSet(SortedSet<E> s) | Constructs a new set containing the same elements and using the same ordering as the specified sorted set. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
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 |
void | clear() | Removes all of the elements from this set. |
ConcurrentSkipListSet<E> | clone() | Returns a shallow copy of this |
boolean | contains(Object o) | Returns |
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 (lowest) element currently in this set. |
E | floor(E e) | Returns the greatest element in this set less than or equal to the given element, or |
NavigableSet<E> | headSet(E toElement) | Returns a view of the portion of this set whose elements are strictly less than |
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 |
E | higher(E e) | Returns the least element in this set strictly greater than the given element, or |
boolean | isEmpty() | Returns |
Iterator<E> | iterator() | Returns an iterator over the elements in this set in ascending order. |
E | last() | Returns the last (highest) element currently in this set. |
E | lower(E e) | Returns the greatest element in this set strictly less than the given element, or |
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. |
Spliterator<E> | spliterator() | Returns a |
NavigableSet<E> | subSet(E fromElement,
boolean fromInclusive,
E toElement,
boolean toInclusive) | Returns a view of the portion of this set whose elements range from |
NavigableSet<E> | subSet(E fromElement,
E toElement) | Returns a view of the portion of this set whose elements range from |
NavigableSet<E> | tailSet(E fromElement) | Returns a view of the portion of this set whose elements are greater than or equal to |
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 |
Methods declared in class java.util.AbstractSet
hashCode
Methods declared in class java.util.AbstractCollection
addAll, containsAll, retainAll, toArray, toArray, toString
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
parallelStream, removeIf, stream, toArray
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.NavigableSet
pollFirst, pollLast
Methods declared in interface java.util.Set
addAll, containsAll, hashCode, retainAll, toArray, toArray
Methods declared in interface java.util.SortedSet
comparator
Constructor Detail
ConcurrentSkipListSet
public ConcurrentSkipListSet()
Constructs a new, empty set that orders its elements according to their natural ordering.
ConcurrentSkipListSet
public ConcurrentSkipListSet(Comparator<? super E> 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. Ifnull
, the natural ordering of the elements will be used.
ConcurrentSkipListSet
public 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
- The elements that will comprise the new set - Throws:
-
ClassCastException
- if the elements inc
are notComparable
, or are not mutually comparable -
NullPointerException
- if the specified collection or any of its elements are null
ConcurrentSkipListSet
public ConcurrentSkipListSet(SortedSet<E> 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 - Throws:
-
NullPointerException
- if the specified sorted set or any of its elements are null
Method Detail
clone
public ConcurrentSkipListSet<E> clone()
Returns a shallow copy of this ConcurrentSkipListSet
instance. (The elements themselves are not cloned.)
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.
- Specified by:
-
size
in interfaceCollection<E>
- Specified by:
-
size
in interfaceSet<E>
- Returns:
- the number of elements in this set
isEmpty
public boolean isEmpty()
Returns true
if this set contains no elements.
- Specified by:
-
isEmpty
in interfaceCollection<E>
- Specified by:
-
isEmpty
in interfaceSet<E>
- Overrides:
-
isEmpty
in classAbstractCollection<E>
- Returns:
-
true
if this set contains no elements
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)
.
- Specified by:
-
contains
in interfaceCollection<E>
- Specified by:
-
contains
in interfaceSet<E>
- Overrides:
-
contains
in classAbstractCollection<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
add
public 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
.
- Specified by:
-
add
in interfaceCollection<E>
- Specified by:
-
add
in interfaceSet<E>
- Overrides:
-
add
in classAbstractCollection<E>
- Parameters:
-
e
- element to be added to this set - Returns:
-
true
if this set did not already contain the specified element - Throws:
-
ClassCastException
- ife
cannot be compared with the elements currently in this set -
NullPointerException
- if the specified element is null
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.)
- Specified by:
-
remove
in interfaceCollection<E>
- Specified by:
-
remove
in interfaceSet<E>
- Overrides:
-
remove
in classAbstractCollection<E>
- Parameters:
-
o
- object to be removed from this set, if present - Returns:
-
true
if this set contained the specified element - Throws:
-
ClassCastException
- ifo
cannot be compared with the elements currently in this set -
NullPointerException
- if the specified element is null
clear
public void clear()
Removes all of the elements from this set.
- Specified by:
-
clear
in interfaceCollection<E>
- Specified by:
-
clear
in interfaceSet<E>
- Overrides:
-
clear
in classAbstractCollection<E>
iterator
public Iterator<E> iterator()
Returns an iterator over the elements in this set in ascending order.
- Specified by:
-
iterator
in interfaceCollection<E>
- Specified by:
-
iterator
in interfaceIterable<E>
- Specified by:
-
iterator
in interfaceNavigableSet<E>
- Specified by:
-
iterator
in interfaceSet<E>
- Specified by:
-
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this set in ascending order
descendingIterator
public Iterator<E> descendingIterator()
Returns an iterator over the elements in this set in descending order.
- Specified by:
-
descendingIterator
in interfaceNavigableSet<E>
- Returns:
- an iterator over the elements in this set in descending order
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.
- Specified by:
-
equals
in interfaceCollection<E>
- Specified by:
-
equals
in interfaceSet<E>
- Overrides:
-
equals
in classAbstractSet<E>
- Parameters:
-
o
- the object to be compared for equality with this set - Returns:
-
true
if the specified object is equal to this set - See Also:
-
Object.hashCode()
,HashMap
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.
- Specified by:
-
removeAll
in interfaceCollection<E>
- Specified by:
-
removeAll
in interfaceSet<E>
- Overrides:
-
removeAll
in classAbstractSet<E>
- 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 class of an element of this set is incompatible with the specified collection (optional) -
NullPointerException
- if the specified collection or any of its elements are null - See Also:
-
AbstractCollection.remove(Object)
,AbstractCollection.contains(Object)
lower
public E lower(E e)
Description copied from interface: NavigableSet
Returns the greatest element in this set strictly less than the given element, or null
if there is no such element.
- Specified by:
-
lower
in interfaceNavigableSet<E>
- Parameters:
-
e
- the value to match - Returns:
- the greatest element less than
e
, ornull
if there is no such element - Throws:
-
ClassCastException
- if the specified element cannot be compared with the elements currently in the set -
NullPointerException
- if the specified element is null
floor
public E floor(E e)
Description copied from interface: NavigableSet
Returns the greatest element in this set less than or equal to the given element, or null
if there is no such element.
- Specified by:
-
floor
in interfaceNavigableSet<E>
- Parameters:
-
e
- the value to match - Returns:
- the greatest element less than or equal to
e
, ornull
if there is no such element - Throws:
-
ClassCastException
- if the specified element cannot be compared with the elements currently in the set -
NullPointerException
- if the specified element is null
ceiling
public E ceiling(E e)
Description copied from interface: NavigableSet
Returns the least element in this set greater than or equal to the given element, or null
if there is no such element.
- Specified by:
-
ceiling
in interfaceNavigableSet<E>
- Parameters:
-
e
- the value to match - Returns:
- the least element greater than or equal to
e
, ornull
if there is no such element - Throws:
-
ClassCastException
- if the specified element cannot be compared with the elements currently in the set -
NullPointerException
- if the specified element is null
higher
public E higher(E e)
Description copied from interface: NavigableSet
Returns the least element in this set strictly greater than the given element, or null
if there is no such element.
- Specified by:
-
higher
in interfaceNavigableSet<E>
- Parameters:
-
e
- the value to match - Returns:
- the least element greater than
e
, ornull
if there is no such element - Throws:
-
ClassCastException
- if the specified element cannot be compared with the elements currently in the set -
NullPointerException
- if the specified element is null
first
public E first()
Description copied from interface: SortedSet
Returns the first (lowest) element currently in this set.
- Specified by:
-
first
in interfaceSortedSet<E>
- Returns:
- the first (lowest) element currently in this set
- Throws:
-
NoSuchElementException
- if this set is empty
last
public E last()
Description copied from interface: SortedSet
Returns the last (highest) element currently in this set.
- Specified by:
-
last
in interfaceSortedSet<E>
- Returns:
- the last (highest) element currently in this set
- Throws:
-
NoSuchElementException
- if this set is empty
subSet
public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)
Description copied from interface: NavigableSet
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
fromInclusive
and toInclusive
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.
- Specified by:
-
subSet
in interfaceNavigableSet<E>
- Parameters:
-
fromElement
- low endpoint of the returned set -
fromInclusive
-true
if the low endpoint is to be included in the returned view -
toElement
- high endpoint of the returned set -
toInclusive
-true
if the high endpoint is to be included in the returned view - Returns:
- a view of the portion of this set whose elements range from
fromElement
, inclusive, totoElement
, exclusive - Throws:
-
ClassCastException
- iffromElement
andtoElement
cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception iffromElement
ortoElement
cannot be compared to elements currently in the set. -
NullPointerException
- iffromElement
ortoElement
is null -
IllegalArgumentException
- iffromElement
is greater thantoElement
; or if this set itself has a restricted range, andfromElement
ortoElement
lies outside the bounds of the range.
headSet
public NavigableSet<E> headSet(E toElement, boolean inclusive)
Description copied from interface: NavigableSet
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.
- Specified by:
-
headSet
in interfaceNavigableSet<E>
- Parameters:
-
toElement
- high endpoint of the returned set -
inclusive
-true
if the high endpoint is to be included in the returned view - Returns:
- a view of the portion of this set whose elements are less than (or equal to, if
inclusive
is true)toElement
- Throws:
-
ClassCastException
- iftoElement
is not compatible with this set's comparator (or, if the set has no comparator, iftoElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iftoElement
cannot be compared to elements currently in the set. -
NullPointerException
- iftoElement
is null -
IllegalArgumentException
- if this set itself has a restricted range, andtoElement
lies outside the bounds of the range
tailSet
public NavigableSet<E> tailSet(E fromElement, boolean inclusive)
Description copied from interface: NavigableSet
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.
- Specified by:
-
tailSet
in interfaceNavigableSet<E>
- Parameters:
-
fromElement
- low endpoint of the returned set -
inclusive
-true
if the low endpoint is to be included in the returned view - Returns:
- a view of the portion of this set whose elements are greater than or equal to
fromElement
- Throws:
-
ClassCastException
- iffromElement
is not compatible with this set's comparator (or, if the set has no comparator, iffromElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iffromElement
cannot be compared to elements currently in the set. -
NullPointerException
- iffromElement
is null -
IllegalArgumentException
- if this set itself has a restricted range, andfromElement
lies outside the bounds of the range
subSet
public NavigableSet<E> subSet(E fromElement, E toElement)
Description copied from interface: NavigableSet
Returns a view of the portion of this set whose elements range from fromElement
, inclusive, to toElement
, exclusive. (If fromElement
and toElement
are equal, the returned set is empty.) 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.
Equivalent to subSet(fromElement, true, toElement, false)
.
- Specified by:
-
subSet
in interfaceNavigableSet<E>
- Specified by:
-
subSet
in interfaceSortedSet<E>
- Parameters:
-
fromElement
- low endpoint (inclusive) of the returned set -
toElement
- high endpoint (exclusive) of the returned set - Returns:
- a view of the portion of this set whose elements range from
fromElement
, inclusive, totoElement
, exclusive - Throws:
-
ClassCastException
- iffromElement
andtoElement
cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception iffromElement
ortoElement
cannot be compared to elements currently in the set. -
NullPointerException
- iffromElement
ortoElement
is null -
IllegalArgumentException
- iffromElement
is greater thantoElement
; or if this set itself has a restricted range, andfromElement
ortoElement
lies outside the bounds of the range
headSet
public NavigableSet<E> headSet(E toElement)
Description copied from interface: NavigableSet
Returns a view of the portion of this set whose elements are strictly less than 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.
Equivalent to headSet(toElement, false)
.
- Specified by:
-
headSet
in interfaceNavigableSet<E>
- Specified by:
-
headSet
in interfaceSortedSet<E>
- Parameters:
-
toElement
- high endpoint (exclusive) of the returned set - Returns:
- a view of the portion of this set whose elements are strictly less than
toElement
- Throws:
-
ClassCastException
- iftoElement
is not compatible with this set's comparator (or, if the set has no comparator, iftoElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iftoElement
cannot be compared to elements currently in the set. -
NullPointerException
- iftoElement
is null -
IllegalArgumentException
- if this set itself has a restricted range, andtoElement
lies outside the bounds of the range
tailSet
public NavigableSet<E> tailSet(E fromElement)
Description copied from interface: NavigableSet
Returns a view of the portion of this set whose elements are greater than or equal to 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.
Equivalent to tailSet(fromElement, true)
.
- Specified by:
-
tailSet
in interfaceNavigableSet<E>
- Specified by:
-
tailSet
in interfaceSortedSet<E>
- Parameters:
-
fromElement
- low endpoint (inclusive) of the returned set - Returns:
- a view of the portion of this set whose elements are greater than or equal to
fromElement
- Throws:
-
ClassCastException
- iffromElement
is not compatible with this set's comparator (or, if the set has no comparator, iffromElement
does not implementComparable
). Implementations may, but are not required to, throw this exception iffromElement
cannot be compared to elements currently in the set. -
NullPointerException
- iffromElement
is null -
IllegalArgumentException
- if this set itself has a restricted range, andfromElement
lies outside the bounds of the range
descendingSet
public 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
.
- Specified by:
-
descendingSet
in interfaceNavigableSet<E>
- Returns:
- a reverse order view of this set
spliterator
public Spliterator<E> spliterator()
Returns a Spliterator
over the elements in this set.
The Spliterator
reports Spliterator.CONCURRENT
, Spliterator.NONNULL
, Spliterator.DISTINCT
, Spliterator.SORTED
and Spliterator.ORDERED
, with an encounter order that is ascending order. Overriding implementations should document the reporting of additional characteristic values.
The spliterator's comparator is null
if the set's comparator is null
. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the set's comparator.
- Specified by:
-
spliterator
in interfaceCollection<E>
- Specified by:
-
spliterator
in interfaceIterable<E>
- Specified by:
-
spliterator
in interfaceSet<E>
- Specified by:
-
spliterator
in interfaceSortedSet<E>
- Returns:
- a
Spliterator
over the elements in this set - Since:
- 1.8