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Android APIs
public class

ConcurrentSkipListMap

extends AbstractMap<K, V>
implements Serializable Cloneable ConcurrentNavigableMap<K, V>
java.lang.Object
   ↳ java.util.AbstractMap<K, V>
     ↳ java.util.concurrent.ConcurrentSkipListMap<K, V>

Class Overview

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 are weakly consistent, returning elements reflecting the state of the map at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations. 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. Additionally, the bulk operations putAll, equals, 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.

Summary

Public Constructors
ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the 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 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 Methods
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 compare keys in this sorted map.
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 key in this sorted 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.
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.
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.
ConcurrentNavigableMap<K, V> headMap(K toKey)
Returns a sorted map over a range of this sorted map with all keys that are less than the specified endKey.

Equivalent to headMap(toKey, false).

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 key in this sorted 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.
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, associate 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.
int size()
Returns the number of key-value mappings in this map.
ConcurrentNavigableMap<K, V> subMap(K fromKey, K toKey)
Returns a sorted map over a range of this sorted map with all keys greater than or equal to the specified startKey and less than the specified endKey.

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 sorted map over a range of this sorted map with all keys that are greater than or equal to the specified startKey.

Equivalent to tailMap(fromKey, true).

Collection<V> values()
Returns a Collection view of the values contained in this map.
[Expand]
Inherited Methods
From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map
From interface java.util.NavigableMap
From interface java.util.SortedMap
From interface java.util.concurrent.ConcurrentMap
From interface java.util.concurrent.ConcurrentNavigableMap

Public Constructors

public ConcurrentSkipListMap ()

Since: API Level 9

Constructs a new, empty map, sorted according to the natural ordering of the keys.

public ConcurrentSkipListMap (Comparator<? super K> comparator)

Since: API Level 9

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.

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

Since: API Level 9

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

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

Since: API Level 9

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)

Since: API Level 9

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)

Since: API Level 9

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 ()

Since: API Level 9

Removes all of the mappings from this map.

public ConcurrentSkipListMap<K, V> clone ()

Since: API Level 9

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 ()

Since: API Level 9

Returns the comparator used to compare keys in this sorted map.

Returns
  • the comparator or null if the natural order is used.

public boolean containsKey (Object key)

Since: API Level 9

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)

Since: API Level 9

Returns true if this map maps one or more keys to the specified value. This operation requires time linear in the map size.

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 ()

Since: API Level 9

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 iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

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

public ConcurrentNavigableMap<K, V> descendingMap ()

Since: API Level 9

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 ()

Since: API Level 9

Returns a Set view of the mappings contained in this map. The set's iterator returns the entries in 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 iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

The Map.Entry elements returned by iterator.next() do not support the setValue operation.

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

public boolean equals (Object o)

Since: API Level 9

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.

Parameters
o object to be compared for equality with this map
Returns
  • true if the specified object is equal to this map

public Entry<K, V> firstEntry ()

Since: API Level 9

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.

Returns
  • an entry with the least key, or null if this map is empty

public K firstKey ()

Since: API Level 9

Returns the first key in this sorted map.

Returns
  • the first key in this sorted map.

public Entry<K, V> floorEntry (K key)

Since: API Level 9

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.

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

public K floorKey (K key)

Since: API Level 9

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

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

public V get (Object key)

Since: API Level 9

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.)

Parameters
key the key.
Returns
  • the value of the mapping with the specified key, or null if no mapping for the specified key is found.
Throws
ClassCastException if the specified key cannot be compared with the keys currently in the map
NullPointerException if the specified key is null

public ConcurrentNavigableMap<K, V> headMap (K toKey, boolean inclusive)

Since: API Level 9

Returns a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Parameters
toKey high endpoint of the keys in the returned map
inclusive true if the high endpoint is to be included in the returned view
Returns
  • a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey

public ConcurrentNavigableMap<K, V> headMap (K toKey)

Since: API Level 9

Returns a sorted map over a range of this sorted map with all keys that are less than the specified endKey. Changes to the returned sorted map are reflected in this sorted map and vice versa.

Note: The returned map will not allow an insertion of a key outside the specified range.

Equivalent to headMap(toKey, false).

Parameters
toKey the high boundary of the range specified.
Returns
  • a sorted map where the keys are less than endKey.

public Entry<K, V> higherEntry (K key)

Since: API Level 9

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.

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

public K higherKey (K key)

Since: API Level 9

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

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

public boolean isEmpty ()

Since: API Level 9

Returns true if this map contains no key-value mappings.

Returns
  • true if this map contains no key-value mappings

public NavigableSet<K> keySet ()

Since: API Level 9

Returns a NavigableSet view of the keys contained in this map. The set's iterator returns the keys in ascending 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 iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

This method is equivalent to method navigableKeySet.

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

public Entry<K, V> lastEntry ()

Since: API Level 9

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.

Returns
  • an entry with the greatest key, or null if this map is empty

public K lastKey ()

Since: API Level 9

Returns the last key in this sorted map.

Returns
  • the last key in this sorted map.

public Entry<K, V> lowerEntry (K key)

Since: API Level 9

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.

Parameters
key the key
Returns
  • an entry with the greatest key less than key, or null if there is no such key
Throws
ClassCastException
NullPointerException if the specified key is null

public K lowerKey (K key)

Since: API Level 9

Returns the greatest key strictly less than the given key, or null if there is no such key.

Parameters
key the key
Returns
  • the greatest key less than key, or null if there is no such key
Throws
ClassCastException
NullPointerException if the specified key is null

public NavigableSet<K> navigableKeySet ()

Since: API Level 9

Returns a NavigableSet view of the keys contained in this map. The set's iterator returns the keys in ascending 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 iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

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

public Entry<K, V> pollFirstEntry ()

Since: API Level 9

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.

Returns
  • the removed first entry of this map, or null if this map is empty

public Entry<K, V> pollLastEntry ()

Since: API Level 9

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.

Returns
  • the removed last entry of this map, or null if this map is empty

public V put (K key, V value)

Since: API Level 9

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.

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

public V putIfAbsent (K key, V value)

Since: API Level 9

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

   if (!map.containsKey(key))
       return map.put(key, value);
   else
       return map.get(key);
except that the action is performed atomically.

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

public boolean remove (Object key, Object value)

Since: API Level 9

Removes the entry for a key only if currently mapped to a given value. This is equivalent to

   if (map.containsKey(key) && map.get(key).equals(value)) {
       map.remove(key);
       return true;
   } else return false;
except that the action is performed atomically.

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

public V remove (Object key)

Since: API Level 9

Removes the mapping for the specified key from this map if present.

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

public boolean replace (K key, V oldValue, V newValue)

Since: API Level 9

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to

   if (map.containsKey(key) && map.get(key).equals(oldValue)) {
       map.put(key, newValue);
       return true;
   } else return false;
except that the action is performed atomically.

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

public V replace (K key, V value)

Since: API Level 9

Replaces the entry for a key only if currently mapped to some value. This is equivalent to

   if (map.containsKey(key)) {
       return map.put(key, value);
   } else return null;
except that the action is performed atomically.

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

public int size ()

Since: API Level 9

Returns the number of key-value mappings in this map. If this map 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 maps, 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.

Returns
  • the number of elements in this map

public ConcurrentNavigableMap<K, V> subMap (K fromKey, K toKey)

Since: API Level 9

Returns a sorted map over a range of this sorted map with all keys greater than or equal to the specified startKey and less than the specified endKey. Changes to the returned sorted map are reflected in this sorted map and vice versa.

Note: The returned map will not allow an insertion of a key outside the specified range.

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

Parameters
fromKey the low boundary of the range (inclusive).
toKey the high boundary of the range (exclusive),
Returns
  • a sorted map with the key from the specified range.

public ConcurrentNavigableMap<K, V> subMap (K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

Since: API Level 9

Returns a view of the portion of this map whose keys range from fromKey to toKey. If fromKey and toKey are equal, the returned map is empty unless fromExclusive and toExclusive are both true. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside of its range, or to construct a submap either of whose endpoints lie outside its range.

Parameters
fromKey low endpoint of the keys in the returned map
fromInclusive true if the low endpoint is to be included in the returned view
toKey high endpoint of the keys in the returned map
toInclusive true if the high endpoint is to be included in the returned view
Returns
  • a view of the portion of this map whose keys range from fromKey to toKey

public ConcurrentNavigableMap<K, V> tailMap (K fromKey, boolean inclusive)

Since: API Level 9

Returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.

The returned map will throw an IllegalArgumentException on an attempt to insert a key outside its range.

Parameters
fromKey low endpoint of the keys in the returned map
inclusive true if the low endpoint is to be included in the returned view
Returns
  • a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey

public ConcurrentNavigableMap<K, V> tailMap (K fromKey)

Since: API Level 9

Returns a sorted map over a range of this sorted map with all keys that are greater than or equal to the specified startKey. Changes to the returned sorted map are reflected in this sorted map and vice versa.

Note: The returned map will not allow an insertion of a key outside the specified range.

Equivalent to tailMap(fromKey, true).

Parameters
fromKey the low boundary of the range specified.
Returns
  • a sorted map where the keys are greater or equal to startKey.

public Collection<V> values ()

Since: API Level 9

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 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 iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Returns
  • a collection of the values contained in this map.