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.
K
lastKey()
Returns the last (highest) key currently in this map.
Entry<K, V>
lowerEntry(K key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
K
lowerKey(K key)
Returns the greatest key strictly less than the given key, or null if there is no such key.
V
merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)
If the specified key is not already associated with a value, associates it with the given value.
NavigableSet<K>
navigableKeySet()
Returns a NavigableSet view of the keys contained in this map.
Entry<K, V>
pollFirstEntry()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
Entry<K, V>
pollLastEntry()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
V
put(K key, V value)
Associates the specified value with the specified key in this map.
V
putIfAbsent(K key, V value)
If the specified key is not already associated with a value, associates it with the given value.
boolean
remove(Object key, Object value)
Removes the entry for a key only if currently mapped to a given value.
V
remove(Object key)
Removes the mapping for the specified key from this map if present.
boolean
replace(K key, V oldValue, V newValue)
Replaces the entry for a key only if currently mapped to a given value.
V
replace(K key, V value)
Replaces the entry for a key only if currently mapped to some value.
void
replaceAll(BiFunction<? super K, ? super V, ? extends V> function)
Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
int
size()
Returns the number of key-value mappings in this map.
ConcurrentNavigableMap<K, V>
subMap(K fromKey, K toKey)
Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.

Equivalent to subMap(fromKey, true, toKey, false).

ConcurrentNavigableMap<K, V>
subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
Returns a view of the portion of this map whose keys range from fromKey to toKey.
ConcurrentNavigableMap<K, V>
tailMap(K fromKey, boolean inclusive)
Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey.
ConcurrentNavigableMap<K, V>
tailMap(K fromKey)
Returns a view of the portion of this map whose keys are greater than or equal to fromKey.

Equivalent to tailMap(fromKey, true).

Collection<V>
values()
Returns a Collection view of the values contained in this map.

Inherited Method Summary

Public Constructors

public ConcurrentSkipListMap ()

Constructs a new, empty map, sorted according to the {@linkplain Comparable natural ordering} of the keys.

public ConcurrentSkipListMap (Comparator<? super K> comparator)

Constructs a new, empty map, sorted according to the specified comparator.

Parameters
comparator the comparator that will be used to order this map. If null, the {@linkplain Comparable natural ordering} of the keys will be used.

public 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.

Parameters
m the map whose mappings are to be placed in this map
Throws
ClassCastException if the keys in m are not Comparable, or are not mutually comparable
NullPointerException if the specified map or any of its keys or values are null

public ConcurrentSkipListMap (SortedMap<K, ? extends V> m)

Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.

Parameters
m the sorted map whose mappings are to be placed in this map, and whose comparator is to be used to sort this map
Throws
NullPointerException if the specified sorted map or any of its keys or values are null

Public Methods

public 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. The returned entry does not support the Entry.setValue method.

Parameters
key the key
Returns
  • an entry with the least key greater than or equal to key, or null if there is no such key
Throws
ClassCastException
NullPointerException if the specified key is null

public K ceilingKey (K key)

Returns the least key greater than or equal to the given key, or null if there is no such key.

Parameters
key the key
Returns
  • the least key greater than or equal to key, or null if there is no such key
Throws
ClassCastException
NullPointerException if the specified key is null

public void clear ()

Removes all of the mappings from this map.

public ConcurrentSkipListMap<K, V> clone ()

Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.)

Returns
  • a shallow copy of this map

public 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.

Returns
  • the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys

public 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). The function is NOT guaranteed to be applied once atomically.

Parameters
key key with which the specified value is to be associated
remappingFunction the function to compute a value
Returns
  • the new value associated with the specified key, or null if none
Throws
NullPointerException if the specified key is null or the remappingFunction is null

public 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. The function is NOT guaranteed to be applied once atomically only if the value is not present.

Parameters
key key with which the specified value is to be associated
mappingFunction the function to compute a value
Returns
  • the current (existing or computed) value associated with the specified key, or null if the computed value is null
Throws
NullPointerException if the specified key is null or the mappingFunction is null

public 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. The function is NOT guaranteed to be applied once atomically.

Parameters
key key with which a value may be associated
remappingFunction the function to compute a value
Returns
  • the new value associated with the specified key, or null if none
Throws
NullPointerException if the specified key is null or the remappingFunction is null

public boolean containsKey (Object key)

Returns true if this map contains a mapping for the specified key.

Parameters
key key whose presence in this map is to be tested
Returns
  • true if this map contains a mapping for the specified key
Throws
ClassCastException if the specified key cannot be compared with the keys currently in the map
NullPointerException if the specified key is null

public boolean containsValue (Object value)

Returns true if this map maps one or more keys to the specified value. This operation requires time linear in the map size. Additionally, it is possible for the map to change during execution of this method, in which case the returned result may be inaccurate.

Parameters
value value whose presence in this map is to be tested
Returns
  • true if a mapping to value exists; false otherwise
Throws
NullPointerException if the specified value is null

public NavigableSet<K> descendingKeySet ()

Returns a reverse order NavigableSet view of the keys contained in this map. The set's iterator returns the keys in descending order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

The view's iterators and spliterators are weakly consistent.

Returns
  • a reverse order navigable set view of the keys in this map

public ConcurrentNavigableMap<K, V> descendingMap ()

Returns a reverse order view of the mappings contained in this map. The descending map is backed by this map, so changes to the map are reflected in the descending map, and vice-versa.

The returned map has an ordering equivalent to Collections.reverseOrder(comparator()). The expression m.descendingMap().descendingMap() returns a view of m essentially equivalent to m.

Returns
  • a reverse order view of this map

public Set<Entry<K, V>> entrySet ()

Returns a Set view of the mappings contained in this map.

The set's iterator returns the entries in ascending key order. The set's spliterator additionally reports Spliterator.CONCURRENT, Spliterator.NONNULL, Spliterator.SORTED and Spliterator.ORDERED, with an encounter order that is ascending key order.

The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

The view's iterators and spliterators are weakly consistent.

The Map.Entry elements traversed by the iterator or spliterator do not support the setValue operation.

Returns
  • a set view of the mappings contained in this map, sorted in ascending key order

public