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Added in API level 9

ConcurrentSkipListMap

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

java.lang.Object
   ↳ java.util.AbstractMap<K, V>
     ↳ java.util.concurrent.ConcurrentSkipListMap<K, V>


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, 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.

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 order the keys in this map, or null if this map uses the 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 methods

From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map
From interface java.util.concurrent.ConcurrentNavigableMap
From interface java.util.concurrent.ConcurrentMap
From interface java.util.NavigableMap
From interface java.util.SortedMap

Public constructors

ConcurrentSkipListMap

Added in API level 9
ConcurrentSkipListMap ()

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

ConcurrentSkipListMap

Added in API level 9
ConcurrentSkipListMap (Comparator<? super K> comparator)

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

Parameters
comparator Comparator: the comparator that will be used to order this map. If null, the natural ordering of the keys will be used.

ConcurrentSkipListMap

Added in API level 9
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 Map: 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

Added in API level 9
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 SortedMap: 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

ceilingEntry

Added in API level 9
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 K: the key
Returns
Entry<K, V> 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

ceilingKey

Added in API level 9
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 K: the key
Returns
K 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

clear

Added in API level 9
void clear ()

Removes all of the mappings from this map.

clone

Added in API level 9
ConcurrentSkipListMap<K, V> clone ()

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

Returns
ConcurrentSkipListMap<K, V> a shallow copy of this map

comparator

Added in API level 9
Comparator<? super K> comparator ()

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

Returns
Comparator<? super K> the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys

compute

Added in API level 24
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 K: key with which the specified value is to be associated
remappingFunction BiFunction: the function to compute a value
Returns
V 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

computeIfAbsent

Added in API level 24
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 K: key with which the specified value is to be associated
mappingFunction Function: the function to compute a value
Returns
V 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

computeIfPresent

Added in API level 24
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 K: key with which a value may be associated
remappingFunction BiFunction: the function to compute a value
Returns
V 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

containsKey

Added in API level 9
boolean containsKey (Object key)

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

Parameters
key Object: key whose presence in this map is to be tested
Returns
boolean 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

containsValue

Added in API level 9
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 Object: value whose presence in this map is to be tested
Returns
boolean true if a mapping to value exists; false otherwise
Throws
NullPointerException if the specified value is null

descendingKeySet

Added in API level 9
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
NavigableSet<K> a reverse order navigable set view of the keys in this map

descendingMap

Added in API level 9
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
ConcurrentNavigableMap<K, V> a reverse order view of this map

entrySet

Added in API level 9
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 CONCURRENT, NONNULL, SORTED and 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
Set<Entry<K, V>> a set view of the mappings contained in this map, sorted in ascending key order

equals

Added in API level 9
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.

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

firstEntry

Added in API level 9
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.

Returns
Entry<K, V> an entry with the least key, or null if this map is empty

firstKey

Added in API level 9
K firstKey ()

Returns the first (lowest) key currently in this map.

Returns
K the first (lowest) key currently in this map
Throws
NoSuchElementException

floorEntry

Added in API level 9
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.

Parameters
key K: the key
Returns
Entry<K, V> 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

floorKey

Added in API level 9
K floorKey (K key)

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

Parameters
key K: the key
Returns
K 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

forEach

Added in API level 24
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. Unless otherwise specified by the implementing class, actions are performed in the order of entry set iteration (if an iteration order is specified.) Exceptions thrown by the action are relayed to the caller.

Parameters
action BiConsumer: The action to be performed for each entry

get

Added in API level 9
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.)

Parameters
key Object: the key whose associated value is to be returned
Returns
V the value to which the specified key is mapped, or null if this map contains 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

getOrDefault

Added in API level 24
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.

Parameters
key Object: the key
defaultValue V: the value to return if this map contains no mapping for the given key
Returns
V the mapping for the key, if present; else the defaultValue
Throws
NullPointerException if the specified key is null

headMap

Added in API level 9
ConcurrentNavigableMap<K, V> headMap (K toKey)

Returns a view of the portion of this map whose keys are strictly less than 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.

Equivalent to headMap(toKey, false).

Parameters
toKey K: high endpoint (exclusive) of the keys in the returned map
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys are strictly less than toKey
Throws
ClassCastException
NullPointerException if toKey is null
IllegalArgumentException

headMap

Added in API level 9
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. 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 K: high endpoint of the keys in the returned map
inclusive boolean: true if the high endpoint is to be included in the returned view
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys are less than (or equal to, if inclusive is true) toKey
Throws
ClassCastException
NullPointerException if toKey is null
IllegalArgumentException

higherEntry

Added in API level 9
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.

Parameters
key K: the key
Returns
Entry<K, V> 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

higherKey

Added in API level 9
K higherKey (K key)

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

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

isEmpty

Added in API level 9
boolean isEmpty ()

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

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

keySet

Added in API level 9
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 CONCURRENT, NONNULL, SORTED and ORDERED, with an encounter order that is ascending key order. The spliterator's comparator (see getComparator()) is null if the map's comparator (see 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.

Returns
NavigableSet<K> a navigable set view of the keys in this map

lastEntry

Added in API level 9
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.

Returns
Entry<K, V> an entry with the greatest key, or null if this map is empty

lastKey

Added in API level 9
K lastKey ()

Returns the last (highest) key currently in this map.

Returns
K the last (highest) key currently in this map
Throws
NoSuchElementException

lowerEntry

Added in API level 9
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.

Parameters
key K: the key
Returns
Entry<K, V> 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

lowerKey

Added in API level 9
K lowerKey (K key)

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

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

merge

Added in API level 24
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.

Parameters
key K: key with which the specified value is to be associated
value V: the value to use if absent
remappingFunction BiFunction: the function to recompute a value if present
Returns
V 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

navigableKeySet

Added in API level 9
NavigableSet<K> navigableKeySet ()

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 iterators and spliterators are weakly consistent.

Returns
NavigableSet<K> a navigable set view of the keys in this map

pollFirstEntry

Added in API level 9
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.

Returns
Entry<K, V> the removed first entry of this map, or null if this map is empty

pollLastEntry

Added in API level 9
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.

Returns
Entry<K, V> the removed last entry of this map, or null if this map is empty

put

Added in API level 9
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.

Parameters
key K: key with which the specified value is to be associated
value V: value to be associated with the specified key
Returns
V 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

putIfAbsent

Added in API level 9
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.

Parameters
key K: key with which the specified value is to be associated
value V: value to be associated with the specified key
Returns
V 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

Added in API level 9
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.

Parameters
key Object: key with which the specified value is associated
value Object: value expected to be associated with the specified key
Returns
boolean 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

remove

Added in API level 9
V remove (Object key)

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

Parameters
key Object: key for which mapping should be removed
Returns
V 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

replace

Added in API level 9
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.

Parameters
key K: key with which the specified value is associated
oldValue V: value expected to be associated with the specified key
newValue V: value to be associated with the specified key
Returns
boolean 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

Added in API level 9
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.

Parameters
key K: key with which the specified value is associated
value V: value to be associated with the specified key
Returns
V 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

replaceAll

Added in API level 24
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. Exceptions thrown by the function are relayed to the caller.

Parameters
function BiFunction: the function to apply to each entry

size

Added in API level 9
int size ()

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
int the number of elements in this map

subMap

Added in API level 9
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. (If fromKey and toKey are equal, the returned map is empty.) 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.

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

Parameters
fromKey K: low endpoint (inclusive) of the keys in the returned map
toKey K: high endpoint (exclusive) of the keys in the returned map
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive
Throws
ClassCastException
NullPointerException if fromKey or toKey is null
IllegalArgumentException

subMap

Added in API level 9
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. If fromKey and toKey are equal, the returned map is empty unless fromInclusive and toInclusive 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 K: low endpoint of the keys in the returned map
fromInclusive boolean: true if the low endpoint is to be included in the returned view
toKey K: high endpoint of the keys in the returned map
toInclusive boolean: true if the high endpoint is to be included in the returned view
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys range from fromKey to toKey
Throws
ClassCastException
NullPointerException if fromKey or toKey is null
IllegalArgumentException

tailMap

Added in API level 9
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. 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 K: low endpoint of the keys in the returned map
inclusive boolean: true if the low endpoint is to be included in the returned view
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey
Throws
ClassCastException
NullPointerException if fromKey is null
IllegalArgumentException

tailMap

Added in API level 9
ConcurrentNavigableMap<K, V> tailMap (K fromKey)

Returns a view of the portion of this map whose keys are greater than or equal to 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.

Equivalent to tailMap(fromKey, true).

Parameters
fromKey K: low endpoint (inclusive) of the keys in the returned map
Returns
ConcurrentNavigableMap<K, V> a view of the portion of this map whose keys are greater than or equal to fromKey
Throws
ClassCastException
NullPointerException if fromKey is null
IllegalArgumentException

values

Added in API level 9
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 CONCURRENT, NONNULL and 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.

Returns
Collection<V> a collection view of the values contained in this map
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