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java.lang.Objectjava.util.AbstractMap
java.util.HashMap
org.apache.commons.collections.FastHashMap
public class FastHashMap
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 java.util.HashMap |
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(java.util.Map map)
Construct a new map with the same mappings as the specified map. |
|
| Method Summary | |
|---|---|
void |
clear()
Remove all mappings from this map. |
java.lang.Object |
clone()
Return a shallow copy of this FastHashMap instance. |
boolean |
containsKey(java.lang.Object key)
Return true if this map contains a mapping for the
specified key. |
boolean |
containsValue(java.lang.Object value)
Return true if this map contains one or more keys mapping
to the specified value. |
java.util.Set |
entrySet()
Return a collection view of the mappings contained in this map. |
boolean |
equals(java.lang.Object o)
Compare the specified object with this list for equality. |
java.lang.Object |
get(java.lang.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. |
java.util.Set |
keySet()
Return a set view of the keys contained in this map. |
java.lang.Object |
put(java.lang.Object key,
java.lang.Object value)
Associate the specified value with the specified key in this map. |
void |
putAll(java.util.Map in)
Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys. |
java.lang.Object |
remove(java.lang.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. |
java.util.Collection |
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 java.util.HashMap 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(java.util.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 java.lang.Object get(java.lang.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 java.util.Mapget in class java.util.HashMapkey - the key whose value is to be returned
public int size()
size in interface java.util.Mapsize in class java.util.HashMappublic boolean isEmpty()
true if this map contains no mappings.
isEmpty in interface java.util.MapisEmpty in class java.util.HashMappublic boolean containsKey(java.lang.Object key)
true if this map contains a mapping for the
specified key.
containsKey in interface java.util.MapcontainsKey in class java.util.HashMapkey - the key to be searched for
public boolean containsValue(java.lang.Object value)
true if this map contains one or more keys mapping
to the specified value.
containsValue in interface java.util.MapcontainsValue in class java.util.HashMapvalue - the value to be searched for
public java.lang.Object put(java.lang.Object key,
java.lang.Object value)
put in interface java.util.Mapput in class java.util.HashMapkey - the key with which the value is to be associatedvalue - the value to be associated with this key
public void putAll(java.util.Map in)
putAll in interface java.util.MapputAll in class java.util.HashMapin - the map whose mappings are to be copiedpublic java.lang.Object remove(java.lang.Object key)
remove in interface java.util.Mapremove in class java.util.HashMapkey - the key whose mapping is to be removed
public void clear()
clear in interface java.util.Mapclear in class java.util.HashMappublic boolean equals(java.lang.Object o)
Map.equals method.
equals in interface java.util.Mapequals in class java.util.AbstractMapo - the object to be compared to this list
public int hashCode()
Map.hashCode method.
hashCode in interface java.util.MaphashCode in class java.util.AbstractMappublic java.lang.Object clone()
FastHashMap instance.
The keys and values themselves are not copied.
clone in class java.util.HashMappublic java.util.Set entrySet()
Map.Entry.
entrySet in interface java.util.MapentrySet in class java.util.HashMappublic java.util.Set keySet()
keySet in interface java.util.MapkeySet in class java.util.HashMappublic java.util.Collection values()
values in interface java.util.Mapvalues in class java.util.HashMap
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