ConcurrentSkipListMap

public class ConcurrentSkipListMap extends AbstractMap<K, V>
implements ConcurrentNavigableMap<K, V> Cloneable Serializable

A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the {@linkplain Comparable natural ordering} of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

This class implements a concurrent variant of SkipLists providing expected average log(n) time cost for the containsKey, get, put and remove operations and their variants. Insertion, removal, update, and access operations safely execute concurrently by multiple threads.

Iterators and spliterators are weakly consistent.

Ascending key ordered views and their iterators are faster than descending ones.

All Map.Entry pairs returned by methods in this class and its views represent snapshots of mappings at the time they were produced. They do not support the Entry.setValue method. (Note however that it is possible to change mappings in the associated map using put, putIfAbsent, or replace, depending on exactly which effect you need.)

Beware that, unlike in most collections, the size method is not a constant-time operation. Because of the asynchronous nature of these maps, 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 putAll, equals, toArray, containsValue, and clear are not guaranteed to be performed atomically. For example, an iterator operating concurrently with a putAll operation might view only some of the added elements.

This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces. Like most other concurrent collections, this class does not permit the use of null keys or values because some null return values cannot be reliably distinguished from the absence of elements.

Public Constructor Summary

ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the {@linkplain Comparable natural ordering} of the keys.
ConcurrentSkipListMap(Comparator<? super K> comparator)
Constructs a new, empty map, sorted according to the specified comparator.
ConcurrentSkipListMap(Map<? extends K, ? extends V> m)
Constructs a new map containing the same mappings as the given map, sorted according to the {@linkplain Comparable natural ordering} of the keys.
ConcurrentSkipListMap(SortedMap<K, ? extends V> m)
Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.

Public Method Summary

Entry<K, V>
ceilingEntry(K key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such entry.
K
ceilingKey(K key)
Returns the least key greater than or equal to the given key, or null if there is no such key.
void
clear()
Removes all of the mappings from this map.
ConcurrentSkipListMap<K, V>
clone()
Returns a shallow copy of this ConcurrentSkipListMap instance.
Comparator<? super K>
comparator()
Returns the comparator used to order the keys in this map, or null if this map uses the {@linkplain Comparable natural ordering} of its keys.
V
compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).
V
computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)
If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless null.
V
computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
If the value for the specified key is present, attempts to compute a new mapping given the key and its current mapped value.
boolean
containsKey(Object key)
Returns true if this map contains a mapping for the specified key.
boolean
containsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
NavigableSet<K>
descendingKeySet()
Returns a reverse order NavigableSet view of the keys contained in this map.
ConcurrentNavigableMap<K, V>
descendingMap()
Returns a reverse order view of the mappings contained in this map.
Set<Entry<K, V>>
entrySet()
Returns a Set view of the mappings contained in this map.
boolean
equals(Object o)
Compares the specified object with this map for equality.
Entry<K, V>
firstEntry()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
K
firstKey()
Returns the first (lowest) key currently in this map.
Entry<K, V>
floorEntry(K key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.
K
floorKey(K key)
Returns the greatest key less than or equal to the given key, or null if there is no such key.
void
forEach(BiConsumer<? super K, ? super V> action)
Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
V
get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
V
getOrDefault(Object key, V defaultValue)
Returns the value to which the specified key is mapped, or the given defaultValue if this map contains no mapping for the key.
ConcurrentNavigableMap<K, V>
headMap(K toKey)
Returns a view of the portion of this map whose keys are strictly less than toKey.

Equivalent to headMap(toKey, false).

ConcurrentNavigableMap<K, V>
headMap(K toKey, boolean inclusive)
Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey.
Entry<K, V>
higherEntry(K key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
K
higherKey(K key)
Returns the least key strictly greater than the given key, or null if there is no such key.
boolean
isEmpty()
Returns true if this map contains no key-value mappings.
NavigableSet<K>
keySet()
Returns a NavigableSet view of the keys contained in this map.
Entry<K, V>
lastEntry()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.