org.apache.commons.collections
Class FastHashMap

java.lang.Object
  extended by java.util.AbstractMap
      extended by java.util.HashMap
          extended by org.apache.commons.collections.FastHashMap
All Implemented Interfaces:
Serializable, Cloneable, Map

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: 555845 $ $Date: 2007-07-13 03:52:05 +0100 (Fri, 13 Jul 2007) $
Author:
Craig R. McClanahan, Stephen Colebourne
See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from class java.util.AbstractMap
AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry
 
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.
 
Methods inherited from class java.util.AbstractMap
toString
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

map

protected HashMap map
The underlying map we are managing.


fast

protected boolean fast
Are we currently operating in "fast" mode?

Constructor Detail

FastHashMap

public FastHashMap()
Construct an empty map.


FastHashMap

public FastHashMap(int capacity)
Construct an empty map with the specified capacity.

Parameters:
capacity - the initial capacity of the empty map

FastHashMap

public FastHashMap(int capacity,
                   float factor)
Construct an empty map with the specified capacity and load factor.

Parameters:
capacity - the initial capacity of the empty map
factor - the load factor of the new map

FastHashMap

public FastHashMap(Map map)
Construct a new map with the same mappings as the specified map.

Parameters:
map - the map whose mappings are to be copied
Method Detail

getFast

public boolean getFast()
Returns true if this map is operating in fast mode.

Returns:
true if this map is operating in fast mode

setFast

public void setFast(boolean fast)
Sets whether this map is operating in fast mode.

Parameters:
fast - true if this map should operate in fast mode

get

public Object get(Object key)
Return the value to which this map maps the specified key. Returns 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.

Specified by:
get in interface Map
Overrides:
get in class HashMap
Parameters:
key - the key whose value is to be returned
Returns:
the value mapped to that key, or null

size

public int size()
Return the number of key-value mappings in this map.

Specified by:
size in interface Map
Overrides:
size in class HashMap
Returns:
the current size of the map

isEmpty

public boolean isEmpty()
Return true if this map contains no mappings.

Specified by:
isEmpty in interface Map
Overrides:
isEmpty in class HashMap
Returns:
is the map currently empty

containsKey

public boolean containsKey(Object key)
Return true if this map contains a mapping for the specified key.

Specified by:
containsKey in interface Map
Overrides:
containsKey in class HashMap
Parameters:
key - the key to be searched for
Returns:
true if the map contains the key

containsValue

public boolean containsValue(Object value)
Return true if this map contains one or more keys mapping to the specified value.

Specified by:
containsValue in interface Map
Overrides:
containsValue in class HashMap
Parameters:
value - the value to be searched for
Returns:
true if the map contains the value

put

public Object put(Object key,
                  Object value)
Associate the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced and returned.

Specified by:
put in interface Map
Overrides:
put in class HashMap
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

putAll

public void putAll(Map in)
Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.

Specified by:
putAll in interface Map
Overrides:
putAll in class HashMap
Parameters:
in - the map whose mappings are to be copied

remove

public Object remove(Object key)
Remove any mapping for this key, and return any previously mapped value.

Specified by:
remove in interface Map
Overrides:
remove in class HashMap
Parameters:
key - the key whose mapping is to be removed
Returns:
the value removed, or null

clear

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

Specified by:
clear in interface Map
Overrides:
clear in class HashMap

equals

public boolean equals(Object o)
Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for the Map.equals method.

Specified by:
equals in interface Map
Overrides:
equals in class AbstractMap
Parameters:
o - the object to be compared to this list
Returns:
true if the two maps are equal

hashCode

public int hashCode()
Return the hash code value for this map. This implementation uses exactly the code that is used to define the list hash function in the documentation for the Map.hashCode method.

Specified by:
hashCode in interface Map
Overrides:
hashCode in class AbstractMap
Returns:
suitable integer hash code

clone

public Object clone()
Return a shallow copy of this FastHashMap instance. The keys and values themselves are not copied.

Overrides:
clone in class HashMap
Returns:
a clone of this map

entrySet

public Set entrySet()
Return a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry.

Specified by:
entrySet in interface Map
Overrides:
entrySet in class HashMap
Returns:
the set of map Map entries

keySet

public Set keySet()
Return a set view of the keys contained in this map.

Specified by:
keySet in interface Map
Overrides:
keySet in class HashMap
Returns:
the set of the Map's keys

values

public Collection values()
Return a collection view of the values contained in this map.

Specified by:
values in interface Map
Overrides:
values in class HashMap
Returns:
the set of the Map's values


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