org.apache.commons.collections
public class FastHashMap extends HashMap
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.
Since: Commons Collections 1.0
Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
Field Summary | |
---|---|
protected boolean | fast
Are we currently operating in "fast" mode? |
protected 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(Map map)
Construct a new map with the same mappings as the specified map.
|
Method Summary | |
---|---|
void | clear()
Remove all mappings from this map. |
Object | 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 | 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. |
Object | 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 | keySet()
Return a set view of the keys contained in this map. |
Object | put(Object key, Object value)
Associate the specified value with the specified key in this map.
|
void | putAll(Map in)
Copy all of the mappings from the specified map to this one, replacing
any mappings with the same keys.
|
Object | 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 | values()
Return a collection view of the values contained in this map. |
Parameters: capacity the initial capacity of the empty map
Parameters: capacity the initial capacity of the empty map factor the load factor of the new map
Parameters: map the map whose mappings are to be copied
FastHashMap
instance.
The keys and values themselves are not copied.
Returns: a clone of this map
true
if this map contains a mapping for the
specified key.
Parameters: key the key to be searched for
Returns: true if the map contains the key
true
if this map contains one or more keys mapping
to the specified value.
Parameters: value the value to be searched for
Returns: true if the map contains the value
Map.Entry
.Map.equals
method.
Parameters: o the object to be compared to this list
Returns: true if the two maps are equal
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.
Parameters: key the key whose value is to be returned
Returns: the value mapped to that key, or null
Returns: true if this map is operating in fast mode
Map.hashCode
method.
Returns: suitable integer hash code
true
if this map contains no mappings.
Returns: is the map currently empty
Parameters: key the key with which the value is to be associated value the value to be associated with this key
Returns: the value previously mapped to the key, or null
Parameters: in the map whose mappings are to be copied
Parameters: key the key whose mapping is to be removed
Returns: the value removed, or null
Parameters: fast true if this map should operate in fast mode
Returns: the current size of the map