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java.lang.Objectjava.util.AbstractMap<K,V>
java.util.HashMap<K,V>
org.apache.commons.collections15.map.FastHashMap<K,V>
public class FastHashMap<K,V>
A customized implementation of java.util.HashMap designed
to operate in a multithreaded environment where the large majority of
method calls are read-only, instead of structural changes. When operating
in "fast" mode, read calls are non-synchronized and write calls perform the
following steps:
When first created, objects of this class default to "slow" mode, where
all accesses of any type are synchronized but no cloning takes place. This
is appropriate for initially populating the collection, followed by a switch
to "fast" mode (by calling setFast(true)) after initialization
is complete.
NOTE: If you are creating and accessing a
HashMap only within a single thread, you should use
java.util.HashMap directly (with no synchronization), for
maximum performance.
NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declaration.
| Field Summary | |
|---|---|
protected boolean |
fast
Are we currently operating in "fast" mode? |
protected HashMap<K,V> |
map
The underlying map we are managing. |
| Constructor Summary | |
|---|---|
FastHashMap()
Construct an empty map. |
|
FastHashMap(int capacity)
Construct an empty map with the specified capacity. |
|
FastHashMap(int capacity,
float factor)
Construct an empty map with the specified capacity and load factor. |
|
FastHashMap(Map map)
Construct a new map with the same mappings as the specified map. |
|
| Method Summary | |
|---|---|
void |
clear()
Remove all mappings from this map. |
FastHashMap<K,V> |
clone()
Return a shallow copy of this FastHashMap instance. |
boolean |
containsKey(Object key)
Return true if this map contains a mapping for the
specified key. |
boolean |
containsValue(Object value)
Return true if this map contains one or more keys mapping
to the specified value. |
Set<Map.Entry<K,V>> |
entrySet()
Return a collection view of the mappings contained in this map. |
boolean |
equals(Object o)
Compare the specified object with this list for equality. |
V |
get(Object key)
Return the value to which this map maps the specified key. |
boolean |
getFast()
Returns true if this map is operating in fast mode. |
int |
hashCode()
Return the hash code value for this map. |
boolean |
isEmpty()
Return true if this map contains no mappings. |
Set<K> |
keySet()
Return a set view of the keys contained in this map. |
V |
put(K key,
V value)
Associate the specified value with the specified key in this map. |
void |
putAll(Map<? extends K,? extends V> in)
Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys. |
V |
remove(Object key)
Remove any mapping for this key, and return any previously mapped value. |
void |
setFast(boolean fast)
Sets whether this map is operating in fast mode. |
int |
size()
Return the number of key-value mappings in this map. |
Collection<V> |
values()
Return a collection view of the values contained in this map. |
| Methods inherited from class java.util.AbstractMap |
|---|
toString |
| Methods inherited from class java.lang.Object |
|---|
finalize, getClass, notify, notifyAll, wait, wait, wait |
| Field Detail |
|---|
protected HashMap<K,V> map
protected boolean fast
| Constructor Detail |
|---|
public FastHashMap()
public FastHashMap(int capacity)
capacity - the initial capacity of the empty map
public FastHashMap(int capacity,
float factor)
capacity - the initial capacity of the empty mapfactor - the load factor of the new mappublic FastHashMap(Map map)
map - the map whose mappings are to be copied| Method Detail |
|---|
public boolean getFast()
public void setFast(boolean fast)
fast - true if this map should operate in fast modepublic V get(Object key)
null if the map contains no mapping for this key, or if
there is a mapping with a value of null. Use the
containsKey() method to disambiguate these cases.
get in interface Map<K,V>get in class HashMap<K,V>key - the key whose value is to be returned
public int size()
size in interface Map<K,V>size in class HashMap<K,V>public boolean isEmpty()
true if this map contains no mappings.
isEmpty in interface Map<K,V>isEmpty in class HashMap<K,V>public boolean containsKey(Object key)
true if this map contains a mapping for the
specified key.
containsKey in interface Map<K,V>containsKey in class HashMap<K,V>key - the key to be searched for
public boolean containsValue(Object value)
true if this map contains one or more keys mapping
to the specified value.
containsValue in interface Map<K,V>containsValue in class HashMap<K,V>value - the value to be searched for
public V put(K key,
V value)
put in interface Map<K,V>put in class HashMap<K,V>key - the key with which the value is to be associatedvalue - the value to be associated with this key
public void putAll(Map<? extends K,? extends V> in)
putAll in interface Map<K,V>putAll in class HashMap<K,V>in - the map whose mappings are to be copiedpublic V remove(Object key)
remove in interface Map<K,V>remove in class HashMap<K,V>key - the key whose mapping is to be removed
public void clear()
clear in interface Map<K,V>clear in class HashMap<K,V>public boolean equals(Object o)
Map.equals method.
equals in interface Map<K,V>equals in class AbstractMap<K,V>o - the object to be compared to this list
public int hashCode()
Map.hashCode method.
hashCode in interface Map<K,V>hashCode in class AbstractMap<K,V>public FastHashMap<K,V> clone()
FastHashMap instance.
The keys and values themselves are not copied.
clone in class HashMap<K,V>public Set<Map.Entry<K,V>> entrySet()
Map.Entry.
entrySet in interface Map<K,V>entrySet in class HashMap<K,V>public Set<K> keySet()
keySet in interface Map<K,V>keySet in class HashMap<K,V>public Collection<V> values()
values in interface Map<K,V>values in class HashMap<K,V>
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