java.util.AbstractMap<K,V>
org.ehcache.internal.concurrent.ConcurrentHashMap<K,V>
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java.lang.Object
K - the type of keys maintained by this mapV - the type of mapped valuespublic class ConcurrentHashMap<K,V>
*** WARNING IF YOU'RE USING THIS CLASS WITH JDK 8 OR ABOVE ***
BY ALL MEANS, DO NOT USE THE spliterator() METHOD
OF THE keySet(), values() or
entrySet() RETURNED OBJECTS. USE THE
_spliterator() ONE INSTEAD.
Hashtable, and
includes versions of methods corresponding to each method of
Hashtable. However, even though all operations are
thread-safe, retrieval operations do not entail locking,
and there is not any support for locking the entire table
in a way that prevents all access. This class is fully
interoperable with Hashtable in programs that rely on its
thread safety but not on its synchronization details.
Retrieval operations (including get) generally do not
block, so may overlap with update operations (including put
and remove). Retrievals reflect the results of the most
recently completed update operations holding upon their
onset. (More formally, an update operation for a given key bears a
happens-before relation with any (non-null) retrieval for
that key reporting the updated value.) For aggregate operations
such as putAll and clear, concurrent retrievals may
reflect insertion or removal of only some entries. Similarly,
Iterators, Spliterators and Enumerations return elements reflecting the
state of the hash table at some point at or since the creation of the
iterator/enumeration. They do not throw ConcurrentModificationException.
However, iterators are designed to be used by only one thread at a time.
Bear in mind that the results of aggregate status methods including
size, isEmpty, and containsValue are typically
useful only when a map is not undergoing concurrent updates in other threads.
Otherwise the results of these methods reflect transient states
that may be adequate for monitoring or estimation purposes, but not
for program control.
The table is dynamically expanded when there are too many
collisions (i.e., keys that have distinct hash codes but fall into
the same slot modulo the table size), with the expected average
effect of maintaining roughly two bins per mapping (corresponding
to a 0.75 load factor threshold for resizing). There may be much
variance around this average as mappings are added and removed, but
overall, this maintains a commonly accepted time/space tradeoff for
hash tables. However, resizing this or any other kind of hash
table may be a relatively slow operation. When possible, it is a
good idea to provide a size estimate as an optional initialCapacity constructor argument. An additional optional
loadFactor constructor argument provides a further means of
customizing initial table capacity by specifying the table density
to be used in calculating the amount of space to allocate for the
given number of elements. Also, for compatibility with previous
versions of this class, constructors may optionally specify an
expected concurrencyLevel as an additional hint for
internal sizing. Note that using many keys with exactly the same
hashCode() is a sure way to slow down performance of any
hash table. To ameliorate impact, when keys are Comparable,
this class may use comparison order among keys to help break ties.
A Set projection of a ConcurrentHashMap may be created
(using newKeySet() or newKeySet(int)), or viewed
(using keySet(Object) when only keys are of interest, and the
mapped values are (perhaps transiently) not used or all take the
same mapping value.
A ConcurrentHashMap can be used as a scalable frequency map (a
form of histogram or multiset) by using
LongAdder values and initializing via
computeIfAbsent. For example, to add a count
to a ConcurrentHashMap<String,LongAdder> freqs, you can use
freqs.computeIfAbsent(key, k -> new LongAdder()).increment();
This class and its views and iterators implement all of the
optional methods of the Map and Iterator
interfaces.
Like Hashtable but unlike HashMap, this class
does not allow null to be used as a key or value.
ConcurrentHashMaps support a set of sequential and parallel bulk
operations that, unlike most Stream methods, are designed
to be safely, and often sensibly, applied even with maps that are
being concurrently updated by other threads; for example, when
computing a snapshot summary of the values in a shared registry.
There are three kinds of operation, each with four forms, accepting
functions with Keys, Values, Entries, and (Key, Value) arguments
and/or return values. Because the elements of a ConcurrentHashMap
are not ordered in any particular way, and may be processed in
different orders in different parallel executions, the correctness
of supplied functions should not depend on any ordering, or on any
other objects or values that may transiently change while
computation is in progress; and except for forEach actions, should
ideally be side-effect-free. Bulk operations on Map.Entry
objects do not support method setValue.
These bulk operations accept a parallelismThreshold
argument. Methods proceed sequentially if the current map size is
estimated to be less than the given threshold. Using a value of
Long.MAX_VALUE suppresses all parallelism. Using a value
of 1 results in maximal parallelism by partitioning into
enough subtasks to fully utilize the ForkJoinPool.commonPool() that is used for all parallel
computations. Normally, you would initially choose one of these
extreme values, and then measure performance of using in-between
values that trade off overhead versus throughput.
The concurrency properties of bulk operations follow
from those of ConcurrentHashMap: Any non-null result returned
from get(key) and related access methods bears a
happens-before relation with the associated insertion or
update. The result of any bulk operation reflects the
composition of these per-element relations (but is not
necessarily atomic with respect to the map as a whole unless it
is somehow known to be quiescent). Conversely, because keys
and values in the map are never null, null serves as a reliable
atomic indicator of the current lack of any result. To
maintain this property, null serves as an implicit basis for
all non-scalar reduction operations. For the double, long, and
int versions, the basis should be one that, when combined with
any other value, returns that other value (more formally, it
should be the identity element for the reduction). Most common
reductions have these properties; for example, computing a sum
with basis 0 or a minimum with basis MAX_VALUE.
Search and transformation functions provided as arguments should similarly return null to indicate the lack of any result (in which case it is not used). In the case of mapped reductions, this also enables transformations to serve as filters, returning null (or, in the case of primitive specializations, the identity basis) if the element should not be combined. You can create compound transformations and filterings by composing them yourself under this "null means there is nothing there now" rule before using them in search or reduce operations.
Methods accepting and/or returning Entry arguments maintain
key-value associations. They may be useful for example when
finding the key for the greatest value. Note that "plain" Entry
arguments can be supplied using new
AbstractMap.SimpleEntry(k,v).
Bulk operations may complete abruptly, throwing an exception encountered in the application of a supplied function. Bear in mind when handling such exceptions that other concurrently executing functions could also have thrown exceptions, or would have done so if the first exception had not occurred.
Speedups for parallel compared to sequential forms are common but not guaranteed. Parallel operations involving brief functions on small maps may execute more slowly than sequential forms if the underlying work to parallelize the computation is more expensive than the computation itself. Similarly, parallelization may not lead to much actual parallelism if all processors are busy performing unrelated tasks.
All arguments to all task methods must be non-null.
This class is a member of the Java Collections Framework.
| Nested Class Summary | |
|---|---|
static class |
ConcurrentHashMap.KeySetView<K,V>
A view of a ConcurrentHashMap as a Set of keys, in
which additions may optionally be enabled by mapping to a
common value. |
| Nested classes/interfaces inherited from class java.util.AbstractMap |
|---|
java.util.AbstractMap.SimpleEntry<K,V>, java.util.AbstractMap.SimpleImmutableEntry<K,V> |
| Nested classes/interfaces inherited from interface java.util.Map |
|---|
java.util.Map.Entry<K,V> |
| Constructor Summary | |
|---|---|
ConcurrentHashMap()
Creates a new, empty map with the default initial table size (16). |
|
ConcurrentHashMap(int initialCapacity)
Creates a new, empty map with an initial table size accommodating the specified number of elements without the need to dynamically resize. |
|
ConcurrentHashMap(int initialCapacity,
float loadFactor)
Creates a new, empty map with an initial table size based on the given number of elements ( initialCapacity) and
initial table density (loadFactor). |
|
ConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel)
Creates a new, empty map with an initial table size based on the given number of elements ( initialCapacity), table
density (loadFactor), and number of concurrently
updating threads (concurrencyLevel). |
|
ConcurrentHashMap(java.util.Map<? extends K,? extends V> m)
Creates a new map with the same mappings as the given map. |
|
| Method Summary | ||
|---|---|---|
void |
clear()
Removes all of the mappings from this map. |
|
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 |
contains(java.lang.Object value)
Deprecated. This method is identical in functionality to containsValue(Object), and exists solely to ensure
full compatibility with class Hashtable,
which supported this method prior to introduction of the
Java Collections framework. |
|
boolean |
containsKey(java.lang.Object key)
Tests if the specified object is a key in this table. |
|
boolean |
containsValue(java.lang.Object value)
Returns true if this map maps one or more keys to the
specified value. |
|
java.util.Enumeration<V> |
elements()
Returns an enumeration of the values in this table. |
|
java.util.Set<java.util.Map.Entry<K,V>> |
entrySet()
Returns a Set view of the mappings contained in this map. |
|
boolean |
equals(java.lang.Object o)
Compares the specified object with this map for equality. |
|
void |
forEach(JSR166Helper.BiConsumer<? super K,? super V> action)
|
|
|
forEach(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
Performs the given action for each non-null transformation of each (key, value). |
|
void |
forEach(long parallelismThreshold,
JSR166Helper.BiConsumer<? super K,? super V> action)
Performs the given action for each (key, value). |
|
|
forEachEntry(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
Performs the given action for each non-null transformation of each entry. |
|
void |
forEachEntry(long parallelismThreshold,
JSR166Helper.Consumer<? super java.util.Map.Entry<K,V>> action)
Performs the given action for each entry. |
|
|
forEachKey(long parallelismThreshold,
Function<? super K,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
Performs the given action for each non-null transformation of each key. |
|
void |
forEachKey(long parallelismThreshold,
JSR166Helper.Consumer<? super K> action)
Performs the given action for each key. |
|
|
forEachValue(long parallelismThreshold,
Function<? super V,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
Performs the given action for each non-null transformation of each value. |
|
void |
forEachValue(long parallelismThreshold,
JSR166Helper.Consumer<? super V> action)
Performs the given action for each value. |
|
V |
get(java.lang.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(java.lang.Object key,
V defaultValue)
Returns the value to which the specified key is mapped, or the given default value if this map contains no mapping for the key. |
|
java.util.Set<java.util.Map.Entry<K,V>> |
getRandomValues(java.util.Random rndm,
int size,
Predicate<java.util.Map.Entry<K,V>> veto)
|
|
int |
hashCode()
Returns the hash code value for this Map, i.e.,
the sum of, for each key-value pair in the map,
key.hashCode() ^ value.hashCode(). |
|
boolean |
isEmpty()
|
|
java.util.Enumeration<K> |
keys()
Returns an enumeration of the keys in this table. |
|
ConcurrentHashMap.KeySetView<K,V> |
keySet()
Returns a Set view of the keys contained in this map. |
|
ConcurrentHashMap.KeySetView<K,V> |
keySet(V mappedValue)
Returns a Set view of the keys in this map, using the
given common mapped value for any additions (i.e., Collection.add(E) and Collection.addAll(Collection)). |
|
long |
mappingCount()
Returns the number of mappings. |
|
V |
merge(K key,
V value,
BiFunction<? super V,? super V,? extends V> remappingFunction)
If the specified key is not already associated with a (non-null) value, associates it with the given value. |
|
static
|
newKeySet()
Creates a new Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE. |
|
static
|
newKeySet(int initialCapacity)
Creates a new Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE. |
|
V |
put(K key,
V value)
Maps the specified key to the specified value in this table. |
|
void |
putAll(java.util.Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this one. |
|
V |
putIfAbsent(K key,
V value)
|
|
|
reduce(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
Returns the result of accumulating the given transformation of all (key, value) pairs using the given reducer to combine values, or null if none. |
|
java.util.Map.Entry<K,V> |
reduceEntries(long parallelismThreshold,
BiFunction<java.util.Map.Entry<K,V>,java.util.Map.Entry<K,V>,? extends java.util.Map.Entry<K,V>> reducer)
Returns the result of accumulating all entries using the given reducer to combine values, or null if none. |
|
|
reduceEntries(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, or null if none. |
|
double |
reduceEntriesToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<java.util.Map.Entry<K,V>> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, and the given basis as an identity value. |
|
int |
reduceEntriesToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<java.util.Map.Entry<K,V>> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, and the given basis as an identity value. |
|
long |
reduceEntriesToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<java.util.Map.Entry<K,V>> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, and the given basis as an identity value. |
|
K |
reduceKeys(long parallelismThreshold,
BiFunction<? super K,? super K,? extends K> reducer)
Returns the result of accumulating all keys using the given reducer to combine values, or null if none. |
|
|
reduceKeys(long parallelismThreshold,
Function<? super K,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, or null if none. |
|
double |
reduceKeysToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<? super K> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, and the given basis as an identity value. |
|
int |
reduceKeysToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<? super K> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, and the given basis as an identity value. |
|
long |
reduceKeysToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<? super K> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, and the given basis as an identity value. |
|
double |
reduceToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleBiFunction<? super K,? super V> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
Returns the result of accumulating the given transformation of all (key, value) pairs using the given reducer to combine values, and the given basis as an identity value. |
|
int |
reduceToInt(long parallelismThreshold,
JSR166Helper.ToIntBiFunction<? super K,? super V> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
Returns the result of accumulating the given transformation of all (key, value) pairs using the given reducer to combine values, and the given basis as an identity value. |
|
long |
reduceToLong(long parallelismThreshold,
JSR166Helper.ToLongBiFunction<? super K,? super V> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
Returns the result of accumulating the given transformation of all (key, value) pairs using the given reducer to combine values, and the given basis as an identity value. |
|
V |
reduceValues(long parallelismThreshold,
BiFunction<? super V,? super V,? extends V> reducer)
Returns the result of accumulating all values using the given reducer to combine values, or null if none. |
|
|
reduceValues(long parallelismThreshold,
Function<? super V,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
Returns the result of accumulating the given transformation of all values using the given reducer to combine values, or null if none. |
|
double |
reduceValuesToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<? super V> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
Returns the result of accumulating the given transformation of all values using the given reducer to combine values, and the given basis as an identity value. |
|
int |
reduceValuesToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<? super V> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
Returns the result of accumulating the given transformation of all values using the given reducer to combine values, and the given basis as an identity value. |
|
long |
reduceValuesToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<? super V> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
Returns the result of accumulating the given transformation of all values using the given reducer to combine values, and the given basis as an identity value. |
|
V |
remove(java.lang.Object key)
Removes the key (and its corresponding value) from this map. |
|
boolean |
remove(java.lang.Object key,
java.lang.Object value)
|
|
V |
replace(K key,
V value)
|
|
boolean |
replace(K key,
V oldValue,
V newValue)
|
|
void |
replaceAll(BiFunction<? super K,? super V,? extends V> function)
|
|
|
search(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> searchFunction)
Returns a non-null result from applying the given search function on each (key, value), or null if none. |
|
|
searchEntries(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> searchFunction)
Returns a non-null result from applying the given search function on each entry, or null if none. |
|
|
searchKeys(long parallelismThreshold,
Function<? super K,? extends U> searchFunction)
Returns a non-null result from applying the given search function on each key, or null if none. |
|
|
searchValues(long parallelismThreshold,
Function<? super V,? extends U> searchFunction)
Returns a non-null result from applying the given search function on each value, or null if none. |
|
int |
size()
|
|
java.lang.String |
toString()
Returns a string representation of this map. |
|
java.util.Collection<V> |
values()
Returns a Collection view of the values contained in this map. |
|
| Methods inherited from class java.util.AbstractMap |
|---|
clone |
| Methods inherited from class java.lang.Object |
|---|
finalize, getClass, notify, notifyAll, wait, wait, wait |
| Constructor Detail |
|---|
public ConcurrentHashMap()
public ConcurrentHashMap(int initialCapacity)
initialCapacity - The implementation performs internal
sizing to accommodate this many elements.
java.lang.IllegalArgumentException - if the initial capacity of
elements is negativepublic ConcurrentHashMap(java.util.Map<? extends K,? extends V> m)
m - the map
public ConcurrentHashMap(int initialCapacity,
float loadFactor)
initialCapacity) and
initial table density (loadFactor).
initialCapacity - the initial capacity. The implementation
performs internal sizing to accommodate this many elements,
given the specified load factor.loadFactor - the load factor (table density) for
establishing the initial table size
java.lang.IllegalArgumentException - if the initial capacity of
elements is negative or the load factor is nonpositive
public ConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel)
initialCapacity), table
density (loadFactor), and number of concurrently
updating threads (concurrencyLevel).
initialCapacity - the initial capacity. The implementation
performs internal sizing to accommodate this many elements,
given the specified load factor.loadFactor - the load factor (table density) for
establishing the initial table sizeconcurrencyLevel - the estimated number of concurrently
updating threads. The implementation may use this value as
a sizing hint.
java.lang.IllegalArgumentException - if the initial capacity is
negative or the load factor or concurrencyLevel are
nonpositive| Method Detail |
|---|
public int size()
size in interface java.util.Map<K,V>size in class java.util.AbstractMap<K,V>public boolean isEmpty()
isEmpty in interface java.util.Map<K,V>isEmpty in class java.util.AbstractMap<K,V>public V get(java.lang.Object key)
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.equals(k),
then this method returns v; otherwise it returns
null. (There can be at most one such mapping.)
get in interface java.util.Map<K,V>get in class java.util.AbstractMap<K,V>java.lang.NullPointerException - if the specified key is nullpublic boolean containsKey(java.lang.Object key)
containsKey in interface java.util.Map<K,V>containsKey in class java.util.AbstractMap<K,V>key - possible key
true if and only if the specified object
is a key in this table, as determined by the
equals method; false otherwise
java.lang.NullPointerException - if the specified key is nullpublic boolean containsValue(java.lang.Object value)
true if this map maps one or more keys to the
specified value. Note: This method may require a full traversal
of the map, and is much slower than method containsKey.
containsValue in interface java.util.Map<K,V>containsValue in class java.util.AbstractMap<K,V>value - value whose presence in this map is to be tested
true if this map maps one or more keys to the
specified value
java.lang.NullPointerException - if the specified value is null
public V put(K key,
V value)
The value can be retrieved by calling the get method
with a key that is equal to the original key.
put in interface java.util.Map<K,V>put in class java.util.AbstractMap<K,V>key - key with which the specified value is to be associatedvalue - value to be associated with the specified key
key, or
null if there was no mapping for key
java.lang.NullPointerException - if the specified key or value is nullpublic void putAll(java.util.Map<? extends K,? extends V> m)
putAll in interface java.util.Map<K,V>putAll in class java.util.AbstractMap<K,V>m - mappings to be stored in this mappublic V remove(java.lang.Object key)
remove in interface java.util.Map<K,V>remove in class java.util.AbstractMap<K,V>key - the key that needs to be removed
key, or
null if there was no mapping for key
java.lang.NullPointerException - if the specified key is nullpublic void clear()
clear in interface java.util.Map<K,V>clear in class java.util.AbstractMap<K,V>public ConcurrentHashMap.KeySetView<K,V> keySet()
Set view of the keys contained in this map.
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 this 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 view's spliterator reports JSR166Helper.Spliterator.CONCURRENT,
JSR166Helper.Spliterator.DISTINCT, and JSR166Helper.Spliterator.NONNULL.
keySet in interface java.util.Map<K,V>keySet in class java.util.AbstractMap<K,V>public java.util.Collection<V> values()
Collection view of the values contained in this map.
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 this 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.
The view's spliterator reports JSR166Helper.Spliterator.CONCURRENT
and JSR166Helper.Spliterator.NONNULL.
values in interface java.util.Map<K,V>values in class java.util.AbstractMap<K,V>public java.util.Set<java.util.Map.Entry<K,V>> entrySet()
Set view of the mappings contained in this map.
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.
The view's iterators and spliterators are weakly consistent.
The view's spliterator reports JSR166Helper.Spliterator.CONCURRENT,
JSR166Helper.Spliterator.DISTINCT, and JSR166Helper.Spliterator.NONNULL.
entrySet in interface java.util.Map<K,V>entrySet in class java.util.AbstractMap<K,V>public int hashCode()
Map, i.e.,
the sum of, for each key-value pair in the map,
key.hashCode() ^ value.hashCode().
hashCode in interface java.util.Map<K,V>hashCode in class java.util.AbstractMap<K,V>public java.lang.String toString()
{}"). Adjacent
mappings are separated by the characters ", " (comma
and space). Each key-value mapping is rendered as the key
followed by an equals sign ("=") followed by the
associated value.
toString in class java.util.AbstractMap<K,V>public boolean equals(java.lang.Object o)
true if the given object is a map with the same
mappings as this map. This operation may return misleading
results if either map is concurrently modified during execution
of this method.
equals in interface java.util.Map<K,V>equals in class java.util.AbstractMap<K,V>o - object to be compared for equality with this map
true if the specified object is equal to this map
public V putIfAbsent(K key,
V value)
putIfAbsent in interface java.util.concurrent.ConcurrentMap<K,V>null if there was no mapping for the key
java.lang.NullPointerException - if the specified key or value is null
public boolean remove(java.lang.Object key,
java.lang.Object value)
remove in interface java.util.concurrent.ConcurrentMap<K,V>java.lang.NullPointerException - if the specified key is null
public boolean replace(K key,
V oldValue,
V newValue)
replace in interface java.util.concurrent.ConcurrentMap<K,V>java.lang.NullPointerException - if any of the arguments are null
public V replace(K key,
V value)
replace in interface java.util.concurrent.ConcurrentMap<K,V>null if there was no mapping for the key
java.lang.NullPointerException - if the specified key or value is null
public V getOrDefault(java.lang.Object key,
V defaultValue)
key - the key whose associated value is to be returneddefaultValue - the value to return if this map contains
no mapping for the given key
java.lang.NullPointerException - if the specified key is nullpublic void forEach(JSR166Helper.BiConsumer<? super K,? super V> action)
public void replaceAll(BiFunction<? super K,? super V,? extends V> function)
public V computeIfAbsent(K key,
Function<? super K,? extends V> mappingFunction)
null. The entire
method invocation is performed atomically, so the function is
applied at most once per key. Some attempted update operations
on this map by other threads may be blocked while computation
is in progress, so the computation should be short and simple,
and must not attempt to update any other mappings of this map.
key - key with which the specified value is to be associatedmappingFunction - the function to compute a value
java.lang.NullPointerException - if the specified key or mappingFunction
is null
java.lang.IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
java.lang.RuntimeException - or Error if the mappingFunction does so,
in which case the mapping is left unestablished
public V computeIfPresent(K key,
BiFunction<? super K,? super V,? extends V> remappingFunction)
key - key with which a value may be associatedremappingFunction - the function to compute a value
java.lang.NullPointerException - if the specified key or remappingFunction
is null
java.lang.IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
java.lang.RuntimeException - or Error if the remappingFunction does so,
in which case the mapping is unchanged
public V compute(K key,
BiFunction<? super K,? super V,? extends V> remappingFunction)
null if there is no current
mapping). The entire method invocation is performed atomically.
Some attempted update operations on this map by other threads
may be blocked while computation is in progress, so the
computation should be short and simple, and must not attempt to
update any other mappings of this Map.
key - key with which the specified value is to be associatedremappingFunction - the function to compute a value
java.lang.NullPointerException - if the specified key or remappingFunction
is null
java.lang.IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
java.lang.RuntimeException - or Error if the remappingFunction does so,
in which case the mapping is unchanged
public V merge(K key,
V value,
BiFunction<? super V,? super V,? extends V> remappingFunction)
null. The entire
method invocation is performed atomically. Some attempted
update operations on this map by other threads may be blocked
while computation is in progress, so the computation should be
short and simple, and must not attempt to update any other
mappings of this Map.
key - key with which the specified value is to be associatedvalue - the value to use if absentremappingFunction - the function to recompute a value if present
java.lang.NullPointerException - if the specified key or the
remappingFunction is null
java.lang.RuntimeException - or Error if the remappingFunction does so,
in which case the mapping is unchanged@Deprecated public boolean contains(java.lang.Object value)
containsValue(Object), and exists solely to ensure
full compatibility with class Hashtable,
which supported this method prior to introduction of the
Java Collections framework.
value - a value to search for
true if and only if some key maps to the
value argument in this table as
determined by the equals method;
false otherwise
java.lang.NullPointerException - if the specified value is nullpublic java.util.Enumeration<K> keys()
keySet()public java.util.Enumeration<V> elements()
values()public long mappingCount()
size() because a ConcurrentHashMap may
contain more mappings than can be represented as an int. The
value returned is an estimate; the actual count may differ if
there are concurrent insertions or removals.
public static <K> ConcurrentHashMap.KeySetView<K,java.lang.Boolean> newKeySet()
Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE.
K - the element type of the returned set
public static <K> ConcurrentHashMap.KeySetView<K,java.lang.Boolean> newKeySet(int initialCapacity)
Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE.
K - the element type of the returned setinitialCapacity - The implementation performs internal
sizing to accommodate this many elements.
java.lang.IllegalArgumentException - if the initial capacity of
elements is negativepublic ConcurrentHashMap.KeySetView<K,V> keySet(V mappedValue)
Set view of the keys in this map, using the
given common mapped value for any additions (i.e., Collection.add(E) and Collection.addAll(Collection)).
This is of course only appropriate if it is acceptable to use
the same value for all additions from this view.
mappedValue - the mapped value to use for any additions
java.lang.NullPointerException - if the mappedValue is null
public void forEach(long parallelismThreshold,
JSR166Helper.BiConsumer<? super K,? super V> action)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelaction - the action
public <U> void forEach(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)action - the action
public <U> U search(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> searchFunction)
U - the return type of the search functionparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelsearchFunction - a function returning a non-null
result on success, else null
public <U> U reduce(long parallelismThreshold,
BiFunction<? super K,? super V,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)reducer - a commutative associative combining function
public double reduceToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleBiFunction<? super K,? super V> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public long reduceToLong(long parallelismThreshold,
JSR166Helper.ToLongBiFunction<? super K,? super V> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public int reduceToInt(long parallelismThreshold,
JSR166Helper.ToIntBiFunction<? super K,? super V> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public void forEachKey(long parallelismThreshold,
JSR166Helper.Consumer<? super K> action)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelaction - the action
public <U> void forEachKey(long parallelismThreshold,
Function<? super K,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)action - the action
public <U> U searchKeys(long parallelismThreshold,
Function<? super K,? extends U> searchFunction)
U - the return type of the search functionparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelsearchFunction - a function returning a non-null
result on success, else null
public K reduceKeys(long parallelismThreshold,
BiFunction<? super K,? super K,? extends K> reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelreducer - a commutative associative combining function
public <U> U reduceKeys(long parallelismThreshold,
Function<? super K,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)reducer - a commutative associative combining function
public double reduceKeysToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<? super K> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public long reduceKeysToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<? super K> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public int reduceKeysToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<? super K> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public void forEachValue(long parallelismThreshold,
JSR166Helper.Consumer<? super V> action)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelaction - the action
public <U> void forEachValue(long parallelismThreshold,
Function<? super V,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)action - the action
public <U> U searchValues(long parallelismThreshold,
Function<? super V,? extends U> searchFunction)
U - the return type of the search functionparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelsearchFunction - a function returning a non-null
result on success, else null
public V reduceValues(long parallelismThreshold,
BiFunction<? super V,? super V,? extends V> reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelreducer - a commutative associative combining function
public <U> U reduceValues(long parallelismThreshold,
Function<? super V,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)reducer - a commutative associative combining function
public double reduceValuesToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<? super V> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public long reduceValuesToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<? super V> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public int reduceValuesToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<? super V> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public void forEachEntry(long parallelismThreshold,
JSR166Helper.Consumer<? super java.util.Map.Entry<K,V>> action)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelaction - the action
public <U> void forEachEntry(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> transformer,
JSR166Helper.Consumer<? super U> action)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)action - the action
public <U> U searchEntries(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> searchFunction)
U - the return type of the search functionparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelsearchFunction - a function returning a non-null
result on success, else null
public java.util.Map.Entry<K,V> reduceEntries(long parallelismThreshold,
BiFunction<java.util.Map.Entry<K,V>,java.util.Map.Entry<K,V>,? extends java.util.Map.Entry<K,V>> reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallelreducer - a commutative associative combining function
public <U> U reduceEntries(long parallelismThreshold,
Function<java.util.Map.Entry<K,V>,? extends U> transformer,
BiFunction<? super U,? super U,? extends U> reducer)
U - the return type of the transformerparallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)reducer - a commutative associative combining function
public double reduceEntriesToDouble(long parallelismThreshold,
JSR166Helper.ToDoubleFunction<java.util.Map.Entry<K,V>> transformer,
double basis,
JSR166Helper.DoubleBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public long reduceEntriesToLong(long parallelismThreshold,
JSR166Helper.ToLongFunction<java.util.Map.Entry<K,V>> transformer,
long basis,
JSR166Helper.LongBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public int reduceEntriesToInt(long parallelismThreshold,
JSR166Helper.ToIntFunction<java.util.Map.Entry<K,V>> transformer,
int basis,
JSR166Helper.IntBinaryOperator reducer)
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in paralleltransformer - a function returning the transformation
for an elementbasis - the identity (initial default value) for the reductionreducer - a commutative associative combining function
public java.util.Set<java.util.Map.Entry<K,V>> getRandomValues(java.util.Random rndm,
int size,
Predicate<java.util.Map.Entry<K,V>> veto)
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