Module java.base
Package java.util.concurrent

Class ConcurrentSkipListMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
java.util.concurrent.ConcurrentSkipListMap<K,V>
Type Parameters:
K - the type of keys maintained by this map
V - the type of mapped values
All Implemented Interfaces:
Serializable, Cloneable, ConcurrentMap<K,V>, ConcurrentNavigableMap<K,V>, Map<K,V>, NavigableMap<K,V>, SortedMap<K,V>
public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V> implements ConcurrentNavigableMap<K,V>, Cloneable, Serializable
A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the 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 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.

This class is a member of the Java Collections Framework.

Since:
1.6
Author:
Doug Lea
See Also:

  • Constructor Details

    • ConcurrentSkipListMap

      public ConcurrentSkipListMap()
      Constructs a new, empty map, sorted according to the natural ordering of the keys.

    • ConcurrentSkipListMap

      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 natural ordering of the keys will be used.

    • ConcurrentSkipListMap

      public ConcurrentSkipListMap(Map<? extends K,? extends V> m)
      Constructs a new map containing the same mappings as the given map, sorted according to the 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

    • ConcurrentSkipListMap

      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

  • Method Details

    • clone

      public ConcurrentSkipListMap<K,V> clone()
      Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.)
      Overrides:
      clone in class AbstractMap<K,V>
      Returns:
      a shallow copy of this map

    • containsKey

      public boolean containsKey(Object key)
      Returns true if this map contains a mapping for the specified key.
      Specified by:
      containsKey in interface Map<K,V>
      Overrides:
      containsKey in class AbstractMap<K,V>
      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

    • get

      public 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.

      More formally, if this map contains a mapping from a key k to a value v such that key compares equal to k according to the map's ordering, then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

      Specified by:
      get in interface Map<K,V>
      Overrides:
      get in class AbstractMap<K,V>
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key is null

    • getOrDefault

      public 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.
      Specified by:
      getOrDefault in interface ConcurrentMap<K,V>
      Specified by:
      getOrDefault in interface Map<K,V>
      Parameters:
      key - the key
      defaultValue - the value to return if this map contains no mapping for the given key
      Returns:
      the mapping for the key, if present; else the defaultValue
      Throws:
      NullPointerException - if the specified key is null
      Since:
      1.8

    • put

      public V put(K key, V value)
      Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
      Specified by:
      put in interface Map<K,V>
      Overrides:
      put in class AbstractMap<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - value to be associated with the specified key
      Returns:
      the previous value associated with the specified key, or null if there was no mapping for the key
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key or value is null

    • remove

      public V remove(Object key)
      Removes the mapping for the specified key from this map if present.
      Specified by:
      remove in interface Map<K,V>
      Overrides:
      remove in class AbstractMap<K,V>
      Parameters:
      key - key for which mapping should be removed
      Returns:
      the previous value associated with the specified key, or null if there was no mapping for the key
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key is null

    • containsValue

      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.
      Specified by:
      containsValue in interface Map<K,V>
      Overrides:
      containsValue in class AbstractMap<K,V>
      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

    • size

      public int size()
      Specified by:
      size in interface Map<K,V>
      Overrides:
      size in class AbstractMap<K,V>

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map<K,V>
      Overrides:
      isEmpty in class AbstractMap<K,V>

    • clear

      public void clear()
      Removes all of the mappings from this map.
      Specified by:
      clear in interface Map<K,V>
      Overrides:
      clear in class AbstractMap<K,V>

    • computeIfAbsent

      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.
      Specified by:
      computeIfAbsent in interface ConcurrentMap<K,V>
      Specified by:
      computeIfAbsent in interface Map<K,V>
      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
      Since:
      1.8

    • computeIfPresent

      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.
      Specified by:
      computeIfPresent in interface ConcurrentMap<K,V>
      Specified by:
      computeIfPresent in interface Map<K,V>
      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
      Since:
      1.8

    • compute

      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.
      Specified by:
      compute in interface ConcurrentMap<K,V>
      Specified by:
      compute in interface Map<K,V>
      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
      Since:
      1.8

    • merge

      public 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. Otherwise, replaces the value with the results of the given remapping function, or removes if null. The function is NOT guaranteed to be applied once atomically.
      Specified by:
      merge in interface ConcurrentMap<K,V>
      Specified by:
      merge in interface Map<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - the value to use if absent
      remappingFunction - the function to recompute a value if present
      Returns:
      the new value associated with the specified key, or null if none
      Throws:
      NullPointerException - if the specified key or value is null or the remappingFunction is null
      Since:
      1.8

    • keySet

      public NavigableSet<K> keySet()
      Returns a NavigableSet view of the keys contained in this map.

      The set's iterator returns the keys in ascending 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 spliterator's comparator is null if the map's comparator is null. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the map's comparator.

      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.

      This method is equivalent to method navigableKeySet.

      Specified by:
      keySet in interface ConcurrentNavigableMap<K,V>
      Specified by:
      keySet in interface Map<K,V>
      Specified by:
      keySet in interface SortedMap<K,V>
      Overrides:
      keySet in class AbstractMap<K,V>
      Returns:
      a navigable set view of the keys in this map

    • values

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

      The collection's iterator returns the values in ascending order of the corresponding keys. The collections's spliterator additionally reports Spliterator.CONCURRENT, Spliterator.NONNULL and Spliterator.ORDERED, with an encounter order that is ascending order of the corresponding keys.

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

      The view's iterators and spliterators are weakly consistent.

      Specified by:
      values in interface Map<K,V>
      Specified by:
      values in interface SortedMap<K,V>
      Overrides:
      values in class AbstractMap<K,V>

    • entrySet

      public Set<Map.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.

      Specified by:
      entrySet in interface Map<K,V>
      Specified by:
      entrySet in interface SortedMap<K,V>
      Specified by:
      entrySet in class AbstractMap<K,V>
      Returns:
      a set view of the mappings contained in this map, sorted in ascending key order

    • descendingMap

      public ConcurrentNavigableMap<K,V> descendingMap()
      Description copied from interface: ConcurrentNavigableMap
      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.

      Specified by:
      descendingMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      descendingMap in interface NavigableMap<K,V>
      Returns:
      a reverse order view of this map

    • descendingKeySet

      public NavigableSet<K> descendingKeySet()
      Description copied from interface: ConcurrentNavigableMap
      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.

      Specified by:
      descendingKeySet in interface ConcurrentNavigableMap<K,V>
      Specified by:
      descendingKeySet in interface NavigableMap<K,V>
      Returns:
      a reverse order navigable set view of the keys in this map

    • equals

      public boolean equals(Object o)
      Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This operation may return misleading results if either map is concurrently modified during execution of this method.
      Specified by:
      equals in interface Map<K,V>
      Overrides:
      equals in class AbstractMap<K,V>
      Parameters:
      o - object to be compared for equality with this map
      Returns:
      true if the specified object is equal to this map

    • putIfAbsent

      public V putIfAbsent(K key, V value)
      If the specified key is not already associated with a value, associates it with the given value. This is equivalent to, for this map: 
       
 if (!map.containsKey(key))
   return map.put(key, value);
 else
   return map.get(key);
      except that the action is performed atomically.
      Specified by:
      putIfAbsent in interface ConcurrentMap<K,V>
      Specified by:
      putIfAbsent in interface Map<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - value to be associated with the specified key
      Returns:
      the previous value associated with the specified key, or null if there was no mapping for the key
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key or value is null

    • remove

      public boolean remove(Object key, Object value)
      Removes the entry for a key only if currently mapped to a given value. This is equivalent to, for this map: 
       
 if (map.containsKey(key)
     && Objects.equals(map.get(key), value)) {
   map.remove(key);
   return true;
 } else {
   return false;
 }
      except that the action is performed atomically.
      Specified by:
      remove in interface ConcurrentMap<K,V>
      Specified by:
      remove in interface Map<K,V>
      Parameters:
      key - key with which the specified value is associated
      value - value expected to be associated with the specified key
      Returns:
      true if the value was removed
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key is null

    • replace

      public boolean replace(K key, V oldValue, V newValue)
      Replaces the entry for a key only if currently mapped to a given value. This is equivalent to, for this map: 
       
 if (map.containsKey(key)
     && Objects.equals(map.get(key), oldValue)) {
   map.put(key, newValue);
   return true;
 } else {
   return false;
 }
      except that the action is performed atomically.
      Specified by:
      replace in interface ConcurrentMap<K,V>
      Specified by:
      replace in interface Map<K,V>
      Parameters:
      key - key with which the specified value is associated
      oldValue - value expected to be associated with the specified key
      newValue - value to be associated with the specified key
      Returns:
      true if the value was replaced
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if any of the arguments are null

    • replace

      public V replace(K key, V value)
      Replaces the entry for a key only if currently mapped to some value. This is equivalent to, for this map: 
       
 if (map.containsKey(key))
   return map.put(key, value);
 else
   return null;
      except that the action is performed atomically.
      Specified by:
      replace in interface ConcurrentMap<K,V>
      Specified by:
      replace in interface Map<K,V>
      Parameters:
      key - key with which the specified value is associated
      value - value to be associated with the specified key
      Returns:
      the previous value associated with the specified key, or null if there was no mapping for the key
      Throws:
      ClassCastException - if the specified key cannot be compared with the keys currently in the map
      NullPointerException - if the specified key or value is null

    • comparator

      public Comparator<? super K> comparator()
      Specified by:
      comparator in interface SortedMap<K,V>

    • firstKey

      public K firstKey()
      Specified by:
      firstKey in interface SortedMap<K,V>
      Throws:
      NoSuchElementException

    • lastKey

      public K lastKey()
      Specified by:
      lastKey in interface SortedMap<K,V>
      Throws:
      NoSuchElementException

    • subMap

      public ConcurrentNavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)
      Specified by:
      subMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      subMap in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if fromKey or toKey is null
      IllegalArgumentException

    • headMap

      public ConcurrentNavigableMap<K,V> headMap(K toKey, boolean inclusive)
      Specified by:
      headMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      headMap in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if toKey is null
      IllegalArgumentException

    • tailMap

      public ConcurrentNavigableMap<K,V> tailMap(K fromKey, boolean inclusive)
      Specified by:
      tailMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      tailMap in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if fromKey is null
      IllegalArgumentException

    • subMap

      public ConcurrentNavigableMap<K,V> subMap(K fromKey, K toKey)
      Specified by:
      subMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      subMap in interface NavigableMap<K,V>
      Specified by:
      subMap in interface SortedMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if fromKey or toKey is null
      IllegalArgumentException

    • headMap

      public ConcurrentNavigableMap<K,V> headMap(K toKey)
      Specified by:
      headMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      headMap in interface NavigableMap<K,V>
      Specified by:
      headMap in interface SortedMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if toKey is null
      IllegalArgumentException

    • tailMap

      public ConcurrentNavigableMap<K,V> tailMap(K fromKey)
      Specified by:
      tailMap in interface ConcurrentNavigableMap<K,V>
      Specified by:
      tailMap in interface NavigableMap<K,V>
      Specified by:
      tailMap in interface SortedMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if fromKey is null
      IllegalArgumentException

    • lowerEntry

      public 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. The returned entry does not support the Entry.setValue method.
      Specified by:
      lowerEntry in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • lowerKey

      public K lowerKey(K key)
      Specified by:
      lowerKey in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • floorEntry

      public 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. The returned entry does not support the Entry.setValue method.
      Specified by:
      floorEntry in interface NavigableMap<K,V>
      Parameters:
      key - the key
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • floorKey

      public K floorKey(K key)
      Specified by:
      floorKey in interface NavigableMap<K,V>
      Parameters:
      key - the key
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • ceilingEntry

      public Map.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.
      Specified by:
      ceilingEntry in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • ceilingKey

      public K ceilingKey(K key)
      Specified by:
      ceilingKey in interface NavigableMap<K,V>
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • higherEntry

      public Map.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. The returned entry does not support the Entry.setValue method.
      Specified by:
      higherEntry in interface NavigableMap<K,V>
      Parameters:
      key - the key
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • higherKey

      public K higherKey(K key)
      Specified by:
      higherKey in interface NavigableMap<K,V>
      Parameters:
      key - the key
      Throws:
      ClassCastException
      NullPointerException - if the specified key is null

    • firstEntry

      public Map.Entry<K,V> firstEntry()
      Returns a key-value mapping associated with the least key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.
      Specified by:
      firstEntry in interface NavigableMap<K,V>

    • lastEntry

      public 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. The returned entry does not support the Entry.setValue method.
      Specified by:
      lastEntry in interface NavigableMap<K,V>

    • pollFirstEntry

      public 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. The returned entry does not support the Entry.setValue method.
      Specified by:
      pollFirstEntry in interface NavigableMap<K,V>

    • pollLastEntry

      public Map.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. The returned entry does not support the Entry.setValue method.
      Specified by:
      pollLastEntry in interface NavigableMap<K,V>