java.util.concurrent
Class ConcurrentHashMap<K,V>

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.util.AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
      extended by java.util.concurrent.ConcurrentHashMap<K,V>
Type Parameters:
K - the type of keys maintained by this map
V - the type of mapped values
All Implemented Interfaces:
Serializable sample code for java.io.Serializable definition code for java.io.Serializable , ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>, Map sample code for java.util.Map definition code for java.util.Map <K,V>

public class ConcurrentHashMap<K,V>
extends AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
implements ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>, Serializable sample code for java.io.Serializable definition code for java.io.Serializable

A hash table supporting full concurrency of retrievals and adjustable expected concurrency for updates. This class obeys the same functional specification as Hashtable sample code for java.util.Hashtable definition code for java.util.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 sample code for java.util.ConcurrentModificationException definition code for java.util.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 sample code for java.util.Map definition code for java.util.Map and Iterator sample code for java.util.Iterator definition code for java.util.Iterator interfaces.

Like Hashtable sample code for java.util.Hashtable definition code for java.util.Hashtable but unlike HashMap sample code for java.util.HashMap definition code for java.util.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.

Since:
1.5
See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map sample code for java.util.Map definition code for java.util.Map
Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>
 
Constructor Summary
ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap() definition code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap() ()
          Creates a new, empty map with a default initial capacity, load factor, and concurrencyLevel.
ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(int) definition code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(int) (int initialCapacity)
          Creates a new, empty map with the specified initial capacity, and with default load factor and concurrencyLevel.
ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(int, float, int) definition code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(int, float, int) (int initialCapacity, float loadFactor, int concurrencyLevel)
          Creates a new, empty map with the specified initial capacity, load factor, and concurrency level.
ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(java.util.Map) definition code for java.util.concurrent.ConcurrentHashMap.ConcurrentHashMap(java.util.Map) (Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
          Creates a new map with the same mappings as the given map.
 
Method Summary
 void clear sample code for java.util.concurrent.ConcurrentHashMap.clear() definition code for java.util.concurrent.ConcurrentHashMap.clear() ()
          Removes all mappings from this map.
 boolean contains sample code for java.util.concurrent.ConcurrentHashMap.contains(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.contains(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  value)
          Legacy method testing if some key maps into the specified value in this table.
 boolean containsKey sample code for java.util.concurrent.ConcurrentHashMap.containsKey(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.containsKey(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Tests if the specified object is a key in this table.
 boolean containsValue sample code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  value)
          Returns true if this map maps one or more keys to the specified value.
 Enumeration sample code for java.util.Enumeration definition code for java.util.Enumeration <V> elements sample code for java.util.concurrent.ConcurrentHashMap.elements() definition code for java.util.concurrent.ConcurrentHashMap.elements() ()
          Returns an enumeration of the values in this table.
 Set sample code for java.util.Set definition code for java.util.Set <Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>> entrySet sample code for java.util.concurrent.ConcurrentHashMap.entrySet() definition code for java.util.concurrent.ConcurrentHashMap.entrySet() ()
          Returns a collection view of the mappings contained in this map.
 V get sample code for java.util.concurrent.ConcurrentHashMap.get(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.get(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Returns the value to which the specified key is mapped in this table.
 boolean isEmpty sample code for java.util.concurrent.ConcurrentHashMap.isEmpty() definition code for java.util.concurrent.ConcurrentHashMap.isEmpty() ()
          Returns true if this map contains no key-value mappings.
 Enumeration sample code for java.util.Enumeration definition code for java.util.Enumeration <K> keys sample code for java.util.concurrent.ConcurrentHashMap.keys() definition code for java.util.concurrent.ConcurrentHashMap.keys() ()
          Returns an enumeration of the keys in this table.
 Set sample code for java.util.Set definition code for java.util.Set <K> keySet sample code for java.util.concurrent.ConcurrentHashMap.keySet() definition code for java.util.concurrent.ConcurrentHashMap.keySet() ()
          Returns a set view of the keys contained in this map.
 V put sample code for java.util.concurrent.ConcurrentHashMap.put(K, V) definition code for java.util.concurrent.ConcurrentHashMap.put(K, V) (K key, V value)
          Maps the specified key to the specified value in this table.
 void putAll sample code for java.util.concurrent.ConcurrentHashMap.putAll(java.util.Map) definition code for java.util.concurrent.ConcurrentHashMap.putAll(java.util.Map) (Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
          Copies all of the mappings from the specified map to this one.
 V putIfAbsent sample code for java.util.concurrent.ConcurrentHashMap.putIfAbsent(K, V) definition code for java.util.concurrent.ConcurrentHashMap.putIfAbsent(K, V) (K key, V value)
          If the specified key is not already associated with a value, associate it with the given value.
 V remove sample code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Removes the key (and its corresponding value) from this table.
 boolean remove sample code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object, java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object, java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key, Object sample code for java.lang.Object definition code for java.lang.Object  value)
          Remove entry for key only if currently mapped to given value.
 V replace sample code for java.util.concurrent.ConcurrentHashMap.replace(K, V) definition code for java.util.concurrent.ConcurrentHashMap.replace(K, V) (K key, V value)
          Replace entry for key only if currently mapped to some value.
 boolean replace sample code for java.util.concurrent.ConcurrentHashMap.replace(K, V, V) definition code for java.util.concurrent.ConcurrentHashMap.replace(K, V, V) (K key, V oldValue, V newValue)
          Replace entry for key only if currently mapped to given value.
 int size sample code for java.util.concurrent.ConcurrentHashMap.size() definition code for java.util.concurrent.ConcurrentHashMap.size() ()
          Returns the number of key-value mappings in this map.
 Collection sample code for java.util.Collection definition code for java.util.Collection <V> values sample code for java.util.concurrent.ConcurrentHashMap.values() definition code for java.util.concurrent.ConcurrentHashMap.values() ()
          Returns a collection view of the values contained in this map.
 
Methods inherited from class java.util.AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap
clone sample code for java.util.AbstractMap.clone() definition code for java.util.AbstractMap.clone() , equals sample code for java.util.AbstractMap.equals(java.lang.Object) definition code for java.util.AbstractMap.equals(java.lang.Object) , hashCode sample code for java.util.AbstractMap.hashCode() definition code for java.util.AbstractMap.hashCode() , toString sample code for java.util.AbstractMap.toString() definition code for java.util.AbstractMap.toString()
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 
Methods inherited from interface java.util.Map sample code for java.util.Map definition code for java.util.Map
equals sample code for java.util.Map.equals(java.lang.Object) definition code for java.util.Map.equals(java.lang.Object) , hashCode sample code for java.util.Map.hashCode() definition code for java.util.Map.hashCode()
 

Constructor Detail

ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap(int, float, int) definition code for java.util.concurrent.ConcurrentHashMap(int, float, int)

public ConcurrentHashMap(int initialCapacity,
                         float loadFactor,
                         int concurrencyLevel)
Creates a new, empty map with the specified initial capacity, load factor, and concurrency level.

Parameters:
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.
Throws:
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.

ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap(int) definition code for java.util.concurrent.ConcurrentHashMap(int)

public ConcurrentHashMap(int initialCapacity)
Creates a new, empty map with the specified initial capacity, and with default load factor and concurrencyLevel.

Parameters:
initialCapacity - the initial capacity. The implementation performs internal sizing to accommodate this many elements.
Throws:
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if the initial capacity of elements is negative.

ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap() definition code for java.util.concurrent.ConcurrentHashMap()

public ConcurrentHashMap()
Creates a new, empty map with a default initial capacity, load factor, and concurrencyLevel.


ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap(java.util.Map<? extends K, ? extends V>) definition code for java.util.concurrent.ConcurrentHashMap(java.util.Map<? extends K, ? extends V>)

public ConcurrentHashMap(Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
Creates a new map with the same mappings as the given map. The map is created with a capacity of twice the number of mappings in the given map or 11 (whichever is greater), and a default load factor and concurrencyLevel.

Parameters:
t - the map
Method Detail

isEmpty sample code for java.util.concurrent.ConcurrentHashMap.isEmpty() definition code for java.util.concurrent.ConcurrentHashMap.isEmpty()

public boolean isEmpty()
Description copied from class: AbstractMap sample code for java.util.AbstractMap.isEmpty() definition code for java.util.AbstractMap.isEmpty()
Returns true if this map contains no key-value mappings.

This implementation returns size() == 0.

Specified by:
isEmpty sample code for java.util.Map.isEmpty() definition code for java.util.Map.isEmpty() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
isEmpty sample code for java.util.AbstractMap.isEmpty() definition code for java.util.AbstractMap.isEmpty() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Returns:
true if this map contains no key-value mappings.

size sample code for java.util.concurrent.ConcurrentHashMap.size() definition code for java.util.concurrent.ConcurrentHashMap.size()

public int size()
Description copied from class: AbstractMap sample code for java.util.AbstractMap.size() definition code for java.util.AbstractMap.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.

This implementation returns entrySet().size().

Specified by:
size sample code for java.util.Map.size() definition code for java.util.Map.size() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
size sample code for java.util.AbstractMap.size() definition code for java.util.AbstractMap.size() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Returns:
the number of key-value mappings in this map.

get sample code for java.util.concurrent.ConcurrentHashMap.get(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.get(java.lang.Object)

public V get(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Returns the value to which the specified key is mapped in this table.

Specified by:
get sample code for java.util.Map.get(java.lang.Object) definition code for java.util.Map.get(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
get sample code for java.util.AbstractMap.get(java.lang.Object) definition code for java.util.AbstractMap.get(java.lang.Object) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Parameters:
key - a key in the table.
Returns:
the value to which the key is mapped in this table; null if the key is not mapped to any value in this table.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key is null.
See Also:
AbstractMap.containsKey(Object) sample code for java.util.AbstractMap.containsKey(java.lang.Object) definition code for java.util.AbstractMap.containsKey(java.lang.Object)

containsKey sample code for java.util.concurrent.ConcurrentHashMap.containsKey(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.containsKey(java.lang.Object)

public boolean containsKey(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Tests if the specified object is a key in this table.

Specified by:
containsKey sample code for java.util.Map.containsKey(java.lang.Object) definition code for java.util.Map.containsKey(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
containsKey sample code for java.util.AbstractMap.containsKey(java.lang.Object) definition code for java.util.AbstractMap.containsKey(java.lang.Object) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <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 sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key is null.

containsValue sample code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object)

public boolean containsValue(Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.util.Map.containsValue(java.lang.Object) definition code for java.util.Map.containsValue(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
containsValue sample code for java.util.AbstractMap.containsValue(java.lang.Object) definition code for java.util.AbstractMap.containsValue(java.lang.Object) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <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 sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the value is null.

contains sample code for java.util.concurrent.ConcurrentHashMap.contains(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.contains(java.lang.Object)

public boolean contains(Object sample code for java.lang.Object definition code for java.lang.Object  value)
Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality to containsValue(java.lang.Object) sample code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.containsValue(java.lang.Object) , and exists solely to ensure full compatibility with class Hashtable sample code for java.util.Hashtable definition code for java.util.Hashtable , 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 sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the value is null.

put sample code for java.util.concurrent.ConcurrentHashMap.put(K, V) definition code for java.util.concurrent.ConcurrentHashMap.put(K, V)

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 sample code for java.util.Map.put(K, V) definition code for java.util.Map.put(K, V) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
put sample code for java.util.AbstractMap.put(K, V) definition code for java.util.AbstractMap.put(K, V) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Parameters:
key - the table key.
value - the value.
Returns:
the previous value of the specified key in this table, or null if it did not have one.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key or value is null.

putIfAbsent sample code for java.util.concurrent.ConcurrentHashMap.putIfAbsent(K, V) definition code for java.util.concurrent.ConcurrentHashMap.putIfAbsent(K, V)

public V putIfAbsent(K key,
                     V value)
If the specified key is not already associated with a value, associate it with the given value. This is equivalent to
   if (!map.containsKey(key)) 
      return map.put(key, value);
   else
      return map.get(key);
 
Except that the action is performed atomically.

Specified by:
putIfAbsent sample code for java.util.concurrent.ConcurrentMap.putIfAbsent(K, V) definition code for java.util.concurrent.ConcurrentMap.putIfAbsent(K, V) in interface ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>
Parameters:
key - key with which the specified value is to be associated.
value - value to be associated with the specified key.
Returns:
previous value associated with specified key, or null if there was no mapping for key.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified key or value is null.

putAll sample code for java.util.concurrent.ConcurrentHashMap.putAll(java.util.Map<? extends K, ? extends V>) definition code for java.util.concurrent.ConcurrentHashMap.putAll(java.util.Map<? extends K, ? extends V>)

public void putAll(Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
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.

Specified by:
putAll sample code for java.util.Map.putAll(java.util.Map) definition code for java.util.Map.putAll(java.util.Map) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
putAll sample code for java.util.AbstractMap.putAll(java.util.Map) definition code for java.util.AbstractMap.putAll(java.util.Map) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Parameters:
t - Mappings to be stored in this map.

remove sample code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object)

public V remove(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Removes the key (and its corresponding value) from this table. This method does nothing if the key is not in the table.

Specified by:
remove sample code for java.util.Map.remove(java.lang.Object) definition code for java.util.Map.remove(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
remove sample code for java.util.AbstractMap.remove(java.lang.Object) definition code for java.util.AbstractMap.remove(java.lang.Object) in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Parameters:
key - the key that needs to be removed.
Returns:
the value to which the key had been mapped in this table, or null if the key did not have a mapping.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key is null.

remove sample code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object, java.lang.Object) definition code for java.util.concurrent.ConcurrentHashMap.remove(java.lang.Object, java.lang.Object)

public boolean remove(Object sample code for java.lang.Object definition code for java.lang.Object  key,
                      Object sample code for java.lang.Object definition code for java.lang.Object  value)
Remove entry for key only if currently mapped to given value. Acts as
 
  if (map.get(key).equals(value)) {
     map.remove(key);
     return true;
 } else return false;
 
except that the action is performed atomically.

Specified by:
remove sample code for java.util.concurrent.ConcurrentMap.remove(java.lang.Object, java.lang.Object) definition code for java.util.concurrent.ConcurrentMap.remove(java.lang.Object, java.lang.Object) in interface ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>
Parameters:
key - key with which the specified value is associated.
value - value associated with the specified key.
Returns:
true if the value was removed
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified key is null.

replace sample code for java.util.concurrent.ConcurrentHashMap.replace(K, V, V) definition code for java.util.concurrent.ConcurrentHashMap.replace(K, V, V)

public boolean replace(K key,
                       V oldValue,
                       V newValue)
Replace entry for key only if currently mapped to given value. Acts as
 
  if (map.get(key).equals(oldValue)) {
     map.put(key, newValue);
     return true;
 } else return false;
 
except that the action is performed atomically.

Specified by:
replace sample code for java.util.concurrent.ConcurrentMap.replace(K, V, V) definition code for java.util.concurrent.ConcurrentMap.replace(K, V, V) in interface ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>
Parameters:
key - key with which the specified value is associated.
oldValue - value expected to be associated with the specified key.
newValue - value to be associated with the specified key.
Returns:
true if the value was replaced
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified key or values are null.

replace sample code for java.util.concurrent.ConcurrentHashMap.replace(K, V) definition code for java.util.concurrent.ConcurrentHashMap.replace(K, V)

public V replace(K key,
                 V value)
Replace entry for key only if currently mapped to some value. Acts as
 
  if ((map.containsKey(key)) {
     return map.put(key, value);
 } else return null;
 
except that the action is performed atomically.

Specified by:
replace sample code for java.util.concurrent.ConcurrentMap.replace(K, V) definition code for java.util.concurrent.ConcurrentMap.replace(K, V) in interface ConcurrentMap sample code for java.util.concurrent.ConcurrentMap definition code for java.util.concurrent.ConcurrentMap <K,V>
Parameters:
key - key with which the specified value is associated.
value - value to be associated with the specified key.
Returns:
previous value associated with specified key, or null if there was no mapping for key.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified key or value is null.

clear sample code for java.util.concurrent.ConcurrentHashMap.clear() definition code for java.util.concurrent.ConcurrentHashMap.clear()

public void clear()
Removes all mappings from this map.

Specified by:
clear sample code for java.util.Map.clear() definition code for java.util.Map.clear() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
clear sample code for java.util.AbstractMap.clear() definition code for java.util.AbstractMap.clear() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>

keySet sample code for java.util.concurrent.ConcurrentHashMap.keySet() definition code for java.util.concurrent.ConcurrentHashMap.keySet()

public Set sample code for java.util.Set definition code for java.util.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 returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException sample code for java.util.ConcurrentModificationException definition code for java.util.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.

Specified by:
keySet sample code for java.util.Map.keySet() definition code for java.util.Map.keySet() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
keySet sample code for java.util.AbstractMap.keySet() definition code for java.util.AbstractMap.keySet() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Returns:
a set view of the keys contained in this map.

values sample code for java.util.concurrent.ConcurrentHashMap.values() definition code for java.util.concurrent.ConcurrentHashMap.values()

public Collection sample code for java.util.Collection definition code for java.util.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 returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException sample code for java.util.ConcurrentModificationException definition code for java.util.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.

Specified by:
values sample code for java.util.Map.values() definition code for java.util.Map.values() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
values sample code for java.util.AbstractMap.values() definition code for java.util.AbstractMap.values() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Returns:
a collection view of the values contained in this map.

entrySet sample code for java.util.concurrent.ConcurrentHashMap.entrySet() definition code for java.util.concurrent.ConcurrentHashMap.entrySet()

public Set sample code for java.util.Set definition code for java.util.Set <Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>> entrySet()
Returns a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry. 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 the map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations. The view's returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException sample code for java.util.ConcurrentModificationException definition code for java.util.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.

Specified by:
entrySet sample code for java.util.Map.entrySet() definition code for java.util.Map.entrySet() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Specified by:
entrySet sample code for java.util.AbstractMap.entrySet() definition code for java.util.AbstractMap.entrySet() in class AbstractMap sample code for java.util.AbstractMap definition code for java.util.AbstractMap <K,V>
Returns:
a collection view of the mappings contained in this map.

keys sample code for java.util.concurrent.ConcurrentHashMap.keys() definition code for java.util.concurrent.ConcurrentHashMap.keys()

public Enumeration sample code for java.util.Enumeration definition code for java.util.Enumeration <K> keys()
Returns an enumeration of the keys in this table.

Returns:
an enumeration of the keys in this table.
See Also:
keySet sample code for java.util.concurrent.ConcurrentHashMap.keySet definition code for java.util.concurrent.ConcurrentHashMap.keySet

elements sample code for java.util.concurrent.ConcurrentHashMap.elements() definition code for java.util.concurrent.ConcurrentHashMap.elements()

public Enumeration sample code for java.util.Enumeration definition code for java.util.Enumeration <V> elements()
Returns an enumeration of the values in this table.

Returns:
an enumeration of the values in this table.
See Also:
values sample code for java.util.concurrent.ConcurrentHashMap.values definition code for java.util.concurrent.ConcurrentHashMap.values