org.apache.commons.collections
Class FastHashMap<K,V>

java.lang.Object
  java.util.AbstractMap<K,V>
      java.util.HashMap<K,V>
          org.apache.commons.collections.FastHashMap<K,V>

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

public class FastHashMap<K,V>
extends HashMap<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:

• Clone the existing collection
• Perform the modification on the clone
• Replace the existing collection with the (modified) clone

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: 1.1.1.1 $ $Date: 2005/05/23 04:33:01 $

Author:

Craig R. McClanahan, Matt Hall, John Watkinson, Stephen Colebourne

See Also:

Serialized Form

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

map

protected HashMap<K,V> 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 V 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<K,V>

Overrides:

get in class HashMap<K,V>

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<K,V>

Overrides:

size in class HashMap<K,V>

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<K,V>

Overrides:

isEmpty in class HashMap<K,V>

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<K,V>

Overrides:

containsKey in class HashMap<K,V>

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<K,V>

Overrides:

containsValue in class HashMap<K,V>

Parameters:

value - the value to be searched for

Returns:

true if the map contains the value

put

public V put(K key,
             V 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<K,V>

Overrides:

put in class HashMap<K,V>

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<? extends K,? extends V> 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<K,V>

Overrides:

putAll in class HashMap<K,V>

Parameters:

in - the map whose mappings are to be copied

remove

public V remove(Object key)

Remove any mapping for this key, and return any previously mapped value.

Specified by:

remove in interface Map<K,V>

Overrides:

remove in class HashMap<K,V>

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<K,V>

Overrides:

clear in class HashMap<K,V>

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<K,V>

Overrides:

equals in class AbstractMap<K,V>

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<K,V>

Overrides:

hashCode in class AbstractMap<K,V>

Returns:

suitable integer hash code

clone

public FastHashMap<K,V> clone()

Return a shallow copy of this FastHashMap instance. The keys and values themselves are not copied.

Overrides:

clone in class HashMap<K,V>

Returns:

a clone of this map

entrySet

public Set<Map.Entry<K,V>> 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<K,V>

Overrides:

entrySet in class HashMap<K,V>

keySet

public Set<K> keySet()

Return a set view of the keys contained in this map.

Specified by:

keySet in interface Map<K,V>

Overrides:

keySet in class HashMap<K,V>

values

public Collection<V> values()

Return a collection view of the values contained in this map.

Specified by:

values in interface Map<K,V>

Overrides:

values in class HashMap<K,V>