Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

This class is a threadsafe implementation of
the java.util.Map interface, and of the atomic
operations added by the ConcurrentMap interface.
This class is intended as a drop-in replacement for
java.util.Hashtable. It is more efficient than
that class, however, because it provides threadsafety without using
synchronized methods that lock the entire data
structure. ConcurrentHashMap allows any number of
concurrent read operations without locking. Locking is required for
updates to a ConcurrentHashMap, but the internal
data structure is segmented so that only the segment being updated is
locked, and reads and writes can proceed concurrently in other
segments. You can specify the number of internal segments with the
concurrencyLevel argument to the
constructor. The default is 16. Set this to the approximate number of
updater threads you expect to access the data structure. Like
Hashtable, ConcurrentHashMap
does not allow null keys or values. (Note that
this differs from the behavior of
java.util.HashMap.)

Figure 16-75. java.util.concurrent.ConcurrentHashMap<K,V>

public class

ConcurrentHashMap<K,V> extends java.util.AbstractMap<K,V>
implements ConcurrentMap<K,V>, Serializable {
// Public Constructors
public

ConcurrentHashMap ( );
public

ConcurrentHashMap (java.util.Map<? extends K,? extends V>

t );
public

ConcurrentHashMap (int

initialCapacity );
public

ConcurrentHashMap (int

initialCapacity , float

loadFactor , int

concurrencyLevel );
// Public Instance Methods
public boolean

contains (Object

value );
public java.util.Enumeration<V>

elements ( );
public java.util.Enumeration<K>

keys ( );
// Methods Implementing ConcurrentMap
public V

putIfAbsent (K

key , V

value );
public boolean

remove (Object

key , Object

value );
public V

replace (K

key , V

value );
public boolean

replace (K

key , V

oldValue , V

newValue );
// Methods Implementing Map
public void

clear ( );
public boolean

containsKey (Object

key );
public boolean

containsValue (Object

value );
public java.util.Set<java.util.Map.Entry<K,V>>

entrySet ( );
public V

get (Object

key );
public boolean

isEmpty ( ); default:true
public java.util.Set<K>

keySet ( );
public V

put (K

key , V

value );
public void

putAll (java.util.Map<? extends K,? extends V>

t );
public V

remove (Object

key );
public int

size ( );
public java.util.Collection<V>

values ( );
}