K - the type of keys maintained by this mapV - the type of mapped valuespublic class BoundedConcurrentHashMap<K,V> extends AbstractMap<K,V> implements ConcurrentMap<K,V>, Serializable
A hash table supporting full concurrency of retrievals and adjustable expected concurrency for
updates. This class obeys the same functional specification as 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. For
aggregate operations such as putAll and clear, concurrent retrievals may
reflect insertion or removal of only some entries. Similarly, Iterators 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.
The allowed concurrency among update operations is guided by
the optional concurrencyLevel constructor argument (default 16), which is used
as a hint for internal sizing. The table is internally partitioned to try to permit the
indicated number of concurrent updates without contention. Because placement in hash tables is
essentially random, the actual concurrency will vary. Ideally, you should choose a value to
accommodate as many threads as will ever concurrently modify the table. Using a significantly
higher value than you need can waste space and time, and a significantly lower value can lead to
thread contention. But overestimates and underestimates within an order of magnitude do not
usually have much noticeable impact. A value of one is appropriate when it is known that only one
thread will modify and all others will only read. Also, resizing this or any other kind of hash
table is a relatively slow operation, so, when possible, it is a good idea to provide estimates
of expected table sizes in constructors.
This class and its views and iterators implement all of the
optional methods of the Map and Iterator
interfaces.
This class is copied from Debezium, (which took it from Hibernate, which took it from Infinispan) and was originally written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the public domain, as explained at http://creativecommons.org/licenses/publicdomain
Like Hashtable but unlike HashMap, this class
does not allow null to be used as a key or value.
| Modifier and Type | Class and Description |
|---|---|
static class |
BoundedConcurrentHashMap.Eviction |
static interface |
BoundedConcurrentHashMap.EvictionListener<K,V> |
static interface |
BoundedConcurrentHashMap.EvictionPolicy<K,V> |
AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>| Constructor and Description |
|---|
BoundedConcurrentHashMap()
Creates a new, empty map with the default maximum capacity
|
BoundedConcurrentHashMap(int capacity)
Creates a new, empty map with the specified maximum capacity, default concurrency level and LRU
eviction policy.
|
BoundedConcurrentHashMap(int capacity,
int concurrencyLevel)
Creates a new, empty map with the specified maximum capacity, load factor, concurrency level
and LRU eviction policy.
|
BoundedConcurrentHashMap(int capacity,
int concurrencyLevel,
BoundedConcurrentHashMap.Eviction evictionStrategy)
Creates a new, empty map with the specified maximum capacity, load factor, concurrency level
and eviction strategy.
|
BoundedConcurrentHashMap(int capacity,
int concurrencyLevel,
BoundedConcurrentHashMap.Eviction evictionStrategy,
BoundedConcurrentHashMap.EvictionListener<K,V> evictionListener)
Creates a new, empty map with the specified maximum capacity, load factor and concurrency
level.
|
| Modifier and Type | Method and Description |
|---|---|
void |
clear()
Removes all of the mappings from this map.
|
boolean |
contains(Object value)
Legacy method testing if some key maps into the specified value in this table.
|
boolean |
containsKey(Object key)
Tests if the specified object is a key in this table.
|
boolean |
containsValue(Object value)
Returns
true if this map maps one or more keys to the specified value. |
Enumeration<V> |
elements()
Returns an enumeration of the values in this table.
|
Set<Map.Entry<K,V>> |
entrySet()
Returns a
Set view of the mappings contained in this map. |
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. |
boolean |
isEmpty()
Returns
true if this map contains no key-value mappings. |
Enumeration<K> |
keys()
Returns an enumeration of the keys in this table.
|
Set<K> |
keySet()
Returns a
Set view of the keys contained in this map. |
V |
put(K key,
V value)
Maps the specified key to the specified value in this table.
|
void |
putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this one.
|
V |
putIfAbsent(K key,
V value) |
V |
remove(Object key)
Removes the key (and its corresponding value) from this map.
|
boolean |
remove(Object key,
Object value) |
V |
replace(K key,
V value) |
boolean |
replace(K key,
V oldValue,
V newValue) |
int |
size()
Returns the number of key-value mappings in this map.
|
Collection<V> |
values()
Returns a
Collection view of the values contained in this map. |
clone, equals, hashCode, toStringfinalize, getClass, notify, notifyAll, wait, wait, waitcompute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, replaceAllpublic BoundedConcurrentHashMap(int capacity,
int concurrencyLevel,
BoundedConcurrentHashMap.Eviction evictionStrategy,
BoundedConcurrentHashMap.EvictionListener<K,V> evictionListener)
capacity - is the upper bound capacity for the number of elements in this mapconcurrencyLevel - the estimated number of concurrently updating threads. The
implementation performs internal sizing to try to accommodate this many
threads.evictionStrategy - the algorithm used to evict elements from this mapevictionListener - the evicton listener callback to be notified about evicted elementsIllegalArgumentException - if the initial capacity is negative or the load factor or
concurrencyLevel are nonpositive.public BoundedConcurrentHashMap(int capacity,
int concurrencyLevel)
capacity - is the upper bound capacity for the number of elements in this mapconcurrencyLevel - the estimated number of concurrently updating threads. The
implementation performs internal sizing to try to accommodate this many
threads.IllegalArgumentException - if the initial capacity is negative or the load factor or
concurrencyLevel are nonpositive.public BoundedConcurrentHashMap(int capacity,
int concurrencyLevel,
BoundedConcurrentHashMap.Eviction evictionStrategy)
capacity - is the upper bound capacity for the number of elements in this mapconcurrencyLevel - the estimated number of concurrently updating threads. The
implementation performs internal sizing to try to accommodate this many
threads.evictionStrategy - the algorithm used to evict elements from this mapIllegalArgumentException - if the initial capacity is negative or the load factor or
concurrencyLevel are nonpositive.public BoundedConcurrentHashMap(int capacity)
capacity - is the upper bound capacity for the number of elements in this mapIllegalArgumentException - if the initial capacity of elements is negative or the load
factor is nonpositivepublic BoundedConcurrentHashMap()
public boolean isEmpty()
true if this map contains no key-value mappings.public int size()
Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.public V get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no
mapping for the key.
More formally, if this map contains a mapping from a key
k to a value v such that key.equals(k), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)
get in interface Map<K,V>get in class AbstractMap<K,V>NullPointerException - if the specified key is nullpublic boolean containsKey(Object key)
containsKey in interface Map<K,V>containsKey in class AbstractMap<K,V>key - possible keytrue if and only if the specified object
is a key in this table, as determined by the
equals method; false otherwise.NullPointerException - if the specified key is nullpublic boolean containsValue(Object value)
true if this map maps one or more keys to the specified value. Note: This
method requires a full internal traversal of the hash table, and so is much slower than method
containsKey.containsValue in interface Map<K,V>containsValue in class AbstractMap<K,V>value - value whose presence in this map is to be testedtrue if this map maps one or more keys to the
specified valueNullPointerException - if the specified value is nullpublic boolean contains(Object value)
containsValue(java.lang.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 fortrue if and only if some key maps to the
value argument in this table as
determined by the equals method;
false otherwiseNullPointerException - if the specified value is nullpublic V put(K key, V value)
Maps the specified key to the specified value in this table. Neither the key nor the value can be null.
The value can be retrieved by calling the get method
with a key that is equal to the original key.
put in interface Map<K,V>put in class AbstractMap<K,V>key - key with which the specified value is to be associatedvalue - value to be associated with the specified keykey, or
null if there was no mapping for keyNullPointerException - if the specified key or value is nullpublic V putIfAbsent(K key, V value)
putIfAbsent in interface ConcurrentMap<K,V>putIfAbsent in interface Map<K,V>null if there was no
mapping for the keyNullPointerException - if the specified key or value is nullpublic void putAll(Map<? extends K,? extends V> m)
public V remove(Object key)
remove in interface Map<K,V>remove in class AbstractMap<K,V>key - the key that needs to be removedkey, or
null if there was no mapping for keyNullPointerException - if the specified key is nullpublic boolean remove(Object key, Object value)
remove in interface ConcurrentMap<K,V>remove in interface Map<K,V>NullPointerException - if the specified key is nullpublic boolean replace(K key, V oldValue, V newValue)
replace in interface ConcurrentMap<K,V>replace in interface Map<K,V>NullPointerException - if any of the arguments are nullpublic V replace(K key, V value)
replace in interface ConcurrentMap<K,V>replace in interface Map<K,V>null if there was no
mapping for the keyNullPointerException - if the specified key or value is nullpublic void clear()
public Set<K> keySet()
Returns a 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 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.
public Collection<V> values()
Returns a 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 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.
public Set<Map.Entry<K,V>> entrySet()
Returns a 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. 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.
public Enumeration<K> keys()
keySet()public Enumeration<V> elements()
values()Copyright © 2025 Confluent, Inc.. All rights reserved.