public class

FastHashMap

extends HashMap
java.lang.Object
   ↳ java.util.AbstractMap
     ↳ java.util.HashMap
       ↳ org.apache.commons.collections.FastHashMap

Class Overview

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.

Summary

Fields
protected boolean fast Are we currently operating in "fast" mode?
protected HashMap map The underlying map we are managing.
Public Constructors
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.
Public Methods
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.
[Expand]
Inherited Methods
From class java.util.HashMap
From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map

Fields

protected boolean fast

Also: Collections

Are we currently operating in "fast" mode?

protected HashMap map

Also: Collections

The underlying map we are managing.

Public Constructors

public FastHashMap ()

Also: Collections

Construct an empty map.

public FastHashMap (int capacity)

Also: Collections

Construct an empty map with the specified capacity.

Parameters
capacity the initial capacity of the empty map

public FastHashMap (int capacity, float factor)

Also: Collections

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

public FastHashMap (Map map)

Also: Collections

Construct a new map with the same mappings as the specified map.

Parameters
map the map whose mappings are to be copied

Public Methods

public void clear ()

Remove all mappings from this map.

public Object clone ()

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

Returns
  • a clone of this map

public boolean containsKey (Object key)

Return 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

public boolean containsValue (Object value)

Return 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

public Set entrySet ()

Return a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry.

Returns
  • the set of map Map entries

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.

Parameters
o the object to be compared to this list
Returns
  • true if the two maps are equal

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.

Parameters
key the key whose value is to be returned
Returns
  • the value mapped to that key, or null

public boolean getFast ()

Also: Collections

Returns true if this map is operating in fast mode.

Returns
  • true if this map is operating in fast mode

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.

Returns
  • suitable integer hash code

public boolean isEmpty ()

Return true if this map contains no mappings.

Returns
  • is the map currently empty

public Set keySet ()

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

Returns
  • the set of the Map's keys

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.

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

public void putAll (Map in)

Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.

Parameters
in the map whose mappings are to be copied

public Object remove (Object key)

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

Parameters
key the key whose mapping is to be removed
Returns
  • the value removed, or null

public void setFast (boolean fast)

Also: Collections

Sets whether this map is operating in fast mode.

Parameters
fast true if this map should operate in fast mode

public int size ()

Return the number of key-value mappings in this map.

Returns
  • the current size of the map

public Collection values ()

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

Returns
  • the set of the Map's values