K - the type of keys maintained by this mapV - the type of mapped valuespublic class BufferedConcurrentHashMap<K,V> extends AbstractMap<K,V> implements ConcurrentMap<K,V>, Serializable
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.
Like Hashtable but unlike HashMap, this class does not allow
null to be used as a key or value.
This class is a member of the Java Collections Framework.
| Modifier and Type | Class and Description |
|---|---|
static class |
BufferedConcurrentHashMap.Eviction |
static interface |
BufferedConcurrentHashMap.EvictionListener<K,V> |
AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>| Constructor and Description |
|---|
BufferedConcurrentHashMap()
Creates a new, empty map with a default initial capacity (16), load factor (0.75) and
concurrencyLevel (16).
|
BufferedConcurrentHashMap(int initialCapacity)
Creates a new, empty map with the specified initial capacity, and with default load factor
(0.75) and concurrencyLevel (16).
|
BufferedConcurrentHashMap(int initialCapacity,
float loadFactor)
Creates a new, empty map with the specified initial capacity and load factor and with the
default concurrencyLevel (16).
|
BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel) |
BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel,
BufferedConcurrentHashMap.Eviction evictionStrategy) |
BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel,
BufferedConcurrentHashMap.Eviction evictionStrategy,
BufferedConcurrentHashMap.EvictionListener<K,V> evictionListener)
Creates a new, empty map with the specified initial capacity, load factor and concurrency
level.
|
BufferedConcurrentHashMap(Map<? extends K,? extends V> m)
Creates a new map with the same mappings as the given map.
|
| 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, toStringpublic BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel,
BufferedConcurrentHashMap.Eviction evictionStrategy,
BufferedConcurrentHashMap.EvictionListener<K,V> evictionListener)
initialCapacity - the initial capacity. The implementation performs internal sizing to accommodate
this many elements.loadFactor - the load factor threshold, used to control resizing. Resizing may be performed
when the average number of elements per bin exceeds this threshold.concurrencyLevel - 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 BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel)
public BufferedConcurrentHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel,
BufferedConcurrentHashMap.Eviction evictionStrategy)
public BufferedConcurrentHashMap(int initialCapacity,
float loadFactor)
initialCapacity - The implementation performs internal sizing to accommodate this many elements.loadFactor - the load factor threshold, used to control resizing. Resizing may be performed
when the average number of elements per bin exceeds this threshold.IllegalArgumentException - if the initial capacity of elements is negative or the load factor is nonpositivepublic BufferedConcurrentHashMap(int initialCapacity)
initialCapacity - the initial capacity. The implementation performs internal sizing to accommodate
this many elements.IllegalArgumentException - if the initial capacity of elements is negative.public BufferedConcurrentHashMap()
public BufferedConcurrentHashMap(Map<? extends K,? extends V> m)
m - the mappublic boolean isEmpty()
public int size()
public V get(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 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 keyNullPointerException - if the specified key is nullpublic boolean containsValue(Object value)
containsValue in interface Map<K,V>containsValue in class AbstractMap<K,V>value - value whose presence in this map is to be testedNullPointerException - 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 forNullPointerException - if the specified value is nullpublic 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 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 keyNullPointerException - if the specified key or value is nullpublic V putIfAbsent(K key, V value)
putIfAbsent in interface ConcurrentMap<K,V>NullPointerException - 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 removedNullPointerException - if the specified key is nullpublic boolean remove(Object key, Object value)
remove in interface ConcurrentMap<K,V>NullPointerException - if the specified key is nullpublic boolean replace(K key, V oldValue, V newValue)
replace in interface ConcurrentMap<K,V>NullPointerException - if any of the arguments are nullpublic V replace(K key, V value)
replace in interface ConcurrentMap<K,V>NullPointerException - if the specified key or value is nullpublic void clear()
public Set<K> 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 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()
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()
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 © 2006–2019 SYSTAP, LLC DBA Blazegraph. All rights reserved.