Class BoundedConcurrentHashMap<K,V>
- java.lang.Object
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- java.util.AbstractMap<K,V>
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- io.debezium.util.BoundedConcurrentHashMap<K,V>
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- Type Parameters:
K
- the type of keys maintained by this mapV
- the type of mapped values
- All Implemented Interfaces:
Serializable
,ConcurrentMap<K,V>
,Map<K,V>
public 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 asHashtable
, 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
andIterator
interfaces.This class is copied 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 unlikeHashMap
, this class does not allow null to be used as a key or value.- Author:
- Doug Lea
- See Also:
- Serialized Form
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Nested Class Summary
Nested Classes Modifier and Type Class Description (package private) class
BoundedConcurrentHashMap.EntryIterator
(package private) class
BoundedConcurrentHashMap.EntrySet
static class
BoundedConcurrentHashMap.Eviction
static interface
BoundedConcurrentHashMap.EvictionListener<K,V>
static interface
BoundedConcurrentHashMap.EvictionPolicy<K,V>
private static class
BoundedConcurrentHashMap.HashEntry<K,V>
ConcurrentHashMap list entry.(package private) class
BoundedConcurrentHashMap.HashIterator
(package private) class
BoundedConcurrentHashMap.KeyIterator
(package private) class
BoundedConcurrentHashMap.KeySet
(package private) static class
BoundedConcurrentHashMap.LIRS<K,V>
private static class
BoundedConcurrentHashMap.LIRSHashEntry<K,V>
Adapted to Infinispan BoundedConcurrentHashMap using LIRS implementation ideas from Charles Fry ([email protected]) See http://code.google.com/p/concurrentlinkedhashmap/source/browse/trunk/src/test/java/com/googlecode/concurrentlinkedhashmap/caches/LirsMap.java for original sources(package private) static class
BoundedConcurrentHashMap.LRU<K,V>
(package private) static class
BoundedConcurrentHashMap.NullEvictionListener<K,V>
(package private) static class
BoundedConcurrentHashMap.NullEvictionPolicy<K,V>
private static class
BoundedConcurrentHashMap.Recency
(package private) static class
BoundedConcurrentHashMap.Segment<K,V>
Segments are specialized versions of hash tables.(package private) class
BoundedConcurrentHashMap.ValueIterator
(package private) class
BoundedConcurrentHashMap.Values
(package private) class
BoundedConcurrentHashMap.WriteThroughEntry
Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying map.-
Nested classes/interfaces inherited from class java.util.AbstractMap
AbstractMap.SimpleEntry<K extends Object,V extends Object>, AbstractMap.SimpleImmutableEntry<K extends Object,V extends Object>
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Field Summary
Fields Modifier and Type Field Description (package private) static int
DEFAULT_CONCURRENCY_LEVEL
The default concurrency level for this table, used when not otherwise specified in a constructor.(package private) static float
DEFAULT_LOAD_FACTOR
The default load factor for this table, used when not otherwise specified in a constructor.(package private) static int
DEFAULT_MAXIMUM_CAPACITY
The default initial capacity for this table, used when not otherwise specified in a constructor.(package private) Set<Map.Entry<K,V>>
entrySet
(package private) Set<K>
keySet
(package private) static int
MAX_SEGMENTS
The maximum number of segments to allow; used to bound constructor arguments.(package private) static int
MAXIMUM_CAPACITY
The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments.(package private) static int
RETRIES_BEFORE_LOCK
Number of unsynchronized retries in size and containsValue methods before resorting to locking.(package private) int
segmentMask
Mask value for indexing into segments.(package private) BoundedConcurrentHashMap.Segment<K,V>[]
segments
The segments, each of which is a specialized hash table(package private) int
segmentShift
Shift value for indexing within segments.private static long
serialVersionUID
(package private) Collection<V>
values
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Constructor Summary
Constructors Constructor Description BoundedConcurrentHashMap()
Creates a new, empty map with the default maximum capacityBoundedConcurrentHashMap(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.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method 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 aSet
view of the mappings contained in this map.V
get(Object key)
Returns the value to which the specified key is mapped, ornull
if this map contains no mapping for the key.private static int
hash(int h)
Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions.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 aSet
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)
private void
readObject(ObjectInputStream s)
Reconstitute the ConcurrentHashMap instance from a stream (i.e., deserialize it).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)
(package private) BoundedConcurrentHashMap.Segment<K,V>
segmentFor(int hash)
Returns the segment that should be used for key with given hashint
size()
Returns the number of key-value mappings in this map.Collection<V>
values()
Returns aCollection
view of the values contained in this map.private void
writeObject(ObjectOutputStream s)
Save the state of the ConcurrentHashMap instance to a stream (i.e., serialize it).-
Methods inherited from class java.util.AbstractMap
clone, equals, hashCode, toString
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Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
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Methods inherited from interface java.util.concurrent.ConcurrentMap
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, replaceAll
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Field Detail
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serialVersionUID
private static final long serialVersionUID
- See Also:
- Constant Field Values
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DEFAULT_MAXIMUM_CAPACITY
static final int DEFAULT_MAXIMUM_CAPACITY
The default initial capacity for this table, used when not otherwise specified in a constructor.- See Also:
- Constant Field Values
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DEFAULT_LOAD_FACTOR
static final float DEFAULT_LOAD_FACTOR
The default load factor for this table, used when not otherwise specified in a constructor.- See Also:
- Constant Field Values
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DEFAULT_CONCURRENCY_LEVEL
static final int DEFAULT_CONCURRENCY_LEVEL
The default concurrency level for this table, used when not otherwise specified in a constructor.- See Also:
- Constant Field Values
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MAXIMUM_CAPACITY
static final int MAXIMUM_CAPACITY
The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments. MUST be a power of two <= 1<<30 to ensure that entries are indexable using ints.- See Also:
- Constant Field Values
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MAX_SEGMENTS
static final int MAX_SEGMENTS
The maximum number of segments to allow; used to bound constructor arguments.- See Also:
- Constant Field Values
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RETRIES_BEFORE_LOCK
static final int RETRIES_BEFORE_LOCK
Number of unsynchronized retries in size and containsValue 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.- See Also:
- Constant Field Values
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segmentMask
final int segmentMask
Mask value for indexing into segments. The upper bits of a key's hash code are used to choose the segment.
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segmentShift
final int segmentShift
Shift value for indexing within segments.
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segments
final BoundedConcurrentHashMap.Segment<K,V>[] segments
The segments, each of which is a specialized hash table
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values
transient Collection<V> values
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Constructor Detail
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BoundedConcurrentHashMap
public 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.- Parameters:
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 elements- Throws:
IllegalArgumentException
- if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
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BoundedConcurrentHashMap
public BoundedConcurrentHashMap(int capacity, int concurrencyLevel)
Creates a new, empty map with the specified maximum capacity, load factor, concurrency level and LRU eviction policy.- Parameters:
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.- Throws:
IllegalArgumentException
- if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
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BoundedConcurrentHashMap
public 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.- Parameters:
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 map- Throws:
IllegalArgumentException
- if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
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BoundedConcurrentHashMap
public BoundedConcurrentHashMap(int capacity)
Creates a new, empty map with the specified maximum capacity, default concurrency level and LRU eviction policy.- Parameters:
capacity
- is the upper bound capacity for the number of elements in this map- Throws:
IllegalArgumentException
- if the initial capacity of elements is negative or the load factor is nonpositive- Since:
- 1.6
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BoundedConcurrentHashMap
public BoundedConcurrentHashMap()
Creates a new, empty map with the default maximum capacity
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Method Detail
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hash
private static int hash(int h)
Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions. This is critical because ConcurrentHashMap uses power-of-two length hash tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper bits.
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segmentFor
final BoundedConcurrentHashMap.Segment<K,V> segmentFor(int hash)
Returns the segment that should be used for key with given hash- Parameters:
hash
- the hash code for the key- Returns:
- the segment
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isEmpty
public boolean isEmpty()
Returns true if this map contains no key-value mappings.
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size
public int size()
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
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get
public V get(Object key)
Returns the value to which the specified key is mapped, ornull
if this map contains no mapping for the key.More formally, if this map contains a mapping from a key
k
to a valuev
such thatkey.equals(k)
, then this method returnsv
; otherwise it returnsnull
. (There can be at most one such mapping.)- Specified by:
get
in interfaceMap<K,V>
- Overrides:
get
in classAbstractMap<K,V>
- Throws:
NullPointerException
- if the specified key is null
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containsKey
public boolean containsKey(Object key)
Tests if the specified object is a key in this table.- Specified by:
containsKey
in interfaceMap<K,V>
- Overrides:
containsKey
in classAbstractMap<K,V>
- Parameters:
key
- possible key- Returns:
- true if and only if the specified object is a key in this table, as determined by the equals method; false otherwise.
- Throws:
NullPointerException
- if the specified key is null
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containsValue
public boolean containsValue(Object value)
Returns 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.- Specified by:
containsValue
in interfaceMap<K,V>
- Overrides:
containsValue
in classAbstractMap<K,V>
- Parameters:
value
- value whose presence in this map is to be tested- Returns:
- true if this map maps one or more keys to the specified value
- Throws:
NullPointerException
- if the specified value is null
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contains
public boolean contains(Object value)
Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality tocontainsValue(java.lang.Object)
, and exists solely to ensure full compatibility with classHashtable
, which supported this method prior to introduction of the Java Collections framework.- Parameters:
value
- a value to search for- Returns:
- true if and only if some key maps to the value argument in this table as determined by the equals method; false otherwise
- Throws:
NullPointerException
- if the specified value is null
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put
public 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.
- Specified by:
put
in interfaceMap<K,V>
- Overrides:
put
in classAbstractMap<K,V>
- Parameters:
key
- key with which the specified value is to be associatedvalue
- value to be associated with the specified key- Returns:
- the previous value associated with key, or null if there was no mapping for key
- Throws:
NullPointerException
- if the specified key or value is null
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putIfAbsent
public V putIfAbsent(K key, V value)
- Specified by:
putIfAbsent
in interfaceConcurrentMap<K,V>
- Specified by:
putIfAbsent
in interfaceMap<K,V>
- Returns:
- the previous value associated with the specified key, or null if there was no mapping for the key
- Throws:
NullPointerException
- if the specified key or value is null
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putAll
public void putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified map.
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remove
public V remove(Object key)
Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the map.- Specified by:
remove
in interfaceMap<K,V>
- Overrides:
remove
in classAbstractMap<K,V>
- Parameters:
key
- the key that needs to be removed- Returns:
- the previous value associated with key, or null if there was no mapping for key
- Throws:
NullPointerException
- if the specified key is null
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remove
public boolean remove(Object key, Object value)
- Specified by:
remove
in interfaceConcurrentMap<K,V>
- Specified by:
remove
in interfaceMap<K,V>
- Throws:
NullPointerException
- if the specified key is null
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replace
public boolean replace(K key, V oldValue, V newValue)
- Specified by:
replace
in interfaceConcurrentMap<K,V>
- Specified by:
replace
in interfaceMap<K,V>
- Throws:
NullPointerException
- if any of the arguments are null
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replace
public V replace(K key, V value)
- Specified by:
replace
in interfaceConcurrentMap<K,V>
- Specified by:
replace
in interfaceMap<K,V>
- Returns:
- the previous value associated with the specified key, or null if there was no mapping for the key
- Throws:
NullPointerException
- if the specified key or value is null
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clear
public void clear()
Removes all of the mappings from this map.
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keySet
public Set<K> keySet()
Returns aSet
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.
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values
public Collection<V> values()
Returns aCollection
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.
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entrySet
public Set<Map.Entry<K,V>> entrySet()
Returns aSet
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.
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keys
public Enumeration<K> keys()
Returns an enumeration of the keys in this table.- Returns:
- an enumeration of the keys in this table
- See Also:
keySet()
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elements
public Enumeration<V> elements()
Returns an enumeration of the values in this table.- Returns:
- an enumeration of the values in this table
- See Also:
values()
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writeObject
private void writeObject(ObjectOutputStream s) throws IOException
Save the state of the ConcurrentHashMap instance to a stream (i.e., serialize it).- Parameters:
s
- the stream- Throws:
IOException
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readObject
private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException
Reconstitute the ConcurrentHashMap instance from a stream (i.e., deserialize it).- Parameters:
s
- the stream- Throws:
IOException
ClassNotFoundException
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