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
java.util.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
../../../../../../../../technotes/guides/collections/index.html">
Java Collections Framework.
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.
e
- element to be added to this set
- true if this set did not already contain the
specified element
clear
public void clear()
Removes all of the elements from this set.
clone
public Object clone()
Returns a shallow copy of this ConcurrentSkipListSet
instance. (The elements themselves are not cloned.)
- 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).
o
- object to be checked for containment in this set
- true if this set contains the specified element
descendingIterator
public Iterator descendingIterator()
Returns an iterator over the elements in this set in descending order.
- descendingIterator in interface NavigableSet
- 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
Collections.reverseOrder
(comparator()).
The expression
s.descendingSet().descendingSet()
returns a
view of
s
essentially equivalent to
s
.
- descendingSet in interface NavigableSet
- 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.
o
- the object to be compared for equality with this set
- true if the specified object is equal to this set
first
public Object first()
isEmpty
public boolean isEmpty()
Returns true if this set contains no elements.
- true if this set contains no elements
iterator
public Iterator iterator()
Returns an iterator over the elements in this set in ascending order.
- iterator in interface NavigableSet
- an iterator over the elements in this set in ascending order
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.)
o
- object to be removed from this set, if present
- 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.
c
- collection containing elements to be removed from this set
- 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.
- the number of elements in this set
subSet
public SortedSet subSet(Object fromElement,
Object toElement)
- subSet in interface NavigableSet