K - the type of keys maintained by this mapV - the type of mapped valuespublic class ConcurrentLinkedHashMap<K,V> extends AbstractMap<K,V> implements ConcurrentMap<K,V>
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 implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which keys were inserted into the map (insertion-order).NOTE: Access order is not supported by this map. Note that insertion order is not affected if a key is re-inserted into the map. (A key k is reinserted into a map m if m.put(k, v) is invoked when m.containsKey(k) would return true immediately prior to the invocation.)
An optional maxCap may be passed to the map constructor to
create bounded map that will remove stale mappings automatically when new mappings
are added to the map.
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.
| Modifier and Type | Class and Description |
|---|---|
static class |
ConcurrentLinkedHashMap.HashEntry<K,V>
ConcurrentHashMap list entry.
|
static class |
ConcurrentLinkedHashMap.QueuePolicy
Defines queue policy for this hash map.
|
AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>| Modifier and Type | Field and Description |
|---|---|
static int |
DFLT_CONCUR_LVL
The default concurrency level for this table, used when not
otherwise specified in a constructor.
|
static int |
DFLT_INIT_CAP
The default initial capacity for this table,
used when not otherwise specified in a constructor.
|
static float |
DFLT_LOAD_FACTOR
The default load factor for this table, used when not
otherwise specified in a constructor.
|
static int |
MAX_CAP_LIMIT
The maximum capacity, used if a higher value is implicitly
specified by either of the constructors with arguments.
|
static int |
MAX_SEGS
The maximum number of segments to allow; used to bound
constructor arguments.
|
static int |
RETRIES_BEFORE_LOCK
Number of unsynchronized retries in
size and containsValue(java.lang.Object)
methods before resorting to locking. |
| Constructor and Description |
|---|
ConcurrentLinkedHashMap()
Creates a new, empty map with a default initial capacity (16),
load factor (0.75) and concurrencyLevel (16).
|
ConcurrentLinkedHashMap(int initCap)
Creates a new, empty map with the specified initial capacity,
and with default load factor (0.75) and concurrencyLevel (16).
|
ConcurrentLinkedHashMap(int initCap,
float loadFactor)
Creates a new, empty map with the specified initial capacity
and load factor and with the default concurrencyLevel (16).
|
ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl)
Creates a new, empty map with the specified initial
capacity, load factor and concurrency level.
|
ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl,
int maxCap)
Creates a new, empty map with the specified initial
capacity, load factor, concurrency level and max capacity.
|
ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl,
int maxCap,
ConcurrentLinkedHashMap.QueuePolicy qPlc)
Creates a new, empty map with the specified initial
capacity, load factor, concurrency level and max capacity.
|
ConcurrentLinkedHashMap(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 val)
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 val)
Returns true if this map maps one or more keys to the
specified value.
|
Enumeration<V> |
descendingElements()
Returns an enumeration of the values in this table in descending order.
|
Set<Map.Entry<K,V>> |
descendingEntrySet()
Returns a
Set view of the mappings contained in this map
in descending order. |
Enumeration<K> |
descendingKeys()
Returns an enumeration of the keys in this table in descending order.
|
Set<K> |
descendingKeySet()
Returns a
Set view of the keys contained in this map
in descending order. |
Collection<V> |
descendingValues()
Returns a
Collection view of the values contained in this map
in descending order. |
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. |
V |
getSafe(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.
|
boolean |
isEmptyx() |
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. |
ConcurrentLinkedHashMap.QueuePolicy |
policy() |
V |
put(K key,
V val)
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 val) |
ConcurrentLinkedDeque8<ConcurrentLinkedHashMap.HashEntry<K,V>> |
queue()
This method is intended for test purposes only.
|
V |
remove(Object key)
Removes the key (and its corresponding value) from this map.
|
boolean |
remove(Object key,
Object val) |
V |
replace(K key,
V val) |
boolean |
replace(K key,
V oldVal,
V newVal) |
V |
replacex(K key,
V oldVal,
V newVal)
Replaces the entry for a key only if currently mapped to a given value.
|
int |
size()
Returns the number of key-value mappings in this map.
|
int |
sizex() |
Collection<V> |
values()
Returns a
Collection view of the values contained in this map. |
clone, equals, hashCode, toStringpublic static final int DFLT_INIT_CAP
public static final float DFLT_LOAD_FACTOR
public static final int DFLT_CONCUR_LVL
public static final int MAX_CAP_LIMIT
public static final int MAX_SEGS
public static final int RETRIES_BEFORE_LOCK
size and containsValue(java.lang.Object)
methods before resorting to locking. This is used to avoid
unbounded retries if tables undergo continuous modification
which would make it impossible to obtain an accurate result.public ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl,
int maxCap,
ConcurrentLinkedHashMap.QueuePolicy qPlc)
initCap - 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.concurLvl - the estimated number of concurrently
updating threads. The implementation performs internal sizing
to try to accommodate this many threads.maxCap - Max capacity (0 for unbounded).qPlc - Queue policy.IllegalArgumentException - if the initial capacity is
negative or the load factor or concurLvl are
non-positive.public ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl,
int maxCap)
initCap - 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.concurLvl - the estimated number of concurrently
updating threads. The implementation performs internal sizing
to try to accommodate this many threads.maxCap - Max capacity (0 for unbounded).IllegalArgumentException - if the initial capacity is
negative or the load factor or concurLvl are
non-positive.public ConcurrentLinkedHashMap(int initCap,
float loadFactor,
int concurLvl)
initCap - 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.concurLvl - 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 concurLvl are
non-positive.public ConcurrentLinkedHashMap(int initCap,
float loadFactor)
initCap - 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 non-positivepublic ConcurrentLinkedHashMap(int initCap)
initCap - the initial capacity. The implementation
performs internal sizing to accommodate this many elements.IllegalArgumentException - if the initial capacity of
elements is negative.public ConcurrentLinkedHashMap()
public ConcurrentLinkedHashMap(Map<? extends K,? extends V> m)
m - the mappublic boolean isEmpty()
public int size()
public int sizex()
public boolean isEmptyx()
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 V getSafe(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.)
In contrast with get(Object) this method acquires
read lock on segment where the key is mapped.
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 val)
containsValue in interface Map<K,V>containsValue in class AbstractMap<K,V>val - value whose presence in this map is to be testedNullPointerException - if the specified value is nullpublic boolean contains(Object val)
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.val - a value to search forNullPointerException - if the specified value is nullpublic V put(K key, V val)
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 associatedval - value to be associated with the specified keyNullPointerException - if the specified key or value is nullpublic V putIfAbsent(K key, V val)
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 val)
remove in interface ConcurrentMap<K,V>NullPointerException - if the specified key is nullpublic boolean replace(K key, V oldVal, V newVal)
replace in interface ConcurrentMap<K,V>NullPointerException - if any of the arguments are nullpublic V replacex(K key, V oldVal, V newVal)
if (map.containsKey(key)) {
if (map.get(key).equals(oldValue)) {
map.put(key, newValue);
return oldValue;
} else
return map.get(key);
} else return null;
except that the action is performed atomically.key - key with which the specified value is associatedoldVal - value expected to be associated with the specified keynewVal - value to be associated with the specified keyoldVal, if value was replaced, non-null previous value if map
contained some other value and null if there were no such key.public V replace(K key, V val)
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 Set<K> descendingKeySet()
Set view of the keys contained in this map
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 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 Collection<V> descendingValues()
Collection view of the values contained in this map
in descending order.
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 Set<Map.Entry<K,V>> descendingEntrySet()
Set view of the mappings contained in this map
in descending order.
The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. The set supports element
removal, which removes the corresponding mapping from the map,
via the Iterator.remove, Set.remove,
removeAll, retainAll, and clear
operations. It does not support the add or
addAll operations.
The view's iterator is a "weakly consistent" iterator
that will never throw ConcurrentModificationException,
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
public Enumeration<K> keys()
keySet()public Enumeration<K> descendingKeys()
keySet()public Enumeration<V> elements()
values()public Enumeration<V> descendingElements()
values()public ConcurrentLinkedDeque8<ConcurrentLinkedHashMap.HashEntry<K,V>> queue()
public ConcurrentLinkedHashMap.QueuePolicy policy()
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