org.apache.commons.collections.map

Class Flat3Map

Implemented Interfaces:
Cloneable, IterableMap, Map, Serializable

public class Flat3Map
extends java.lang.Object
implements IterableMap, Serializable, Cloneable

A Map implementation that stores data in simple fields until the size is greater than 3.

This map is designed for performance and can outstrip HashMap. It also has good garbage collection characteristics.

The design uses two distinct modes of operation - flat and delegate. While the map is size 3 or less, operations map straight onto fields using switch statements. Once size 4 is reached, the map switches to delegate mode and only switches back when cleared. In delegate mode, all operations are forwarded straight to a HashMap resulting in the 5% performance loss.

The performance gains on puts are due to not needing to create a Map Entry object. This is a large saving not only in performance but in garbage collection.

Whilst in flat mode this map is also easy for the garbage collector to dispatch. This is because it contains no complex objects or arrays which slow the progress.

Do not use Flat3Map if the size is likely to grow beyond 3.

Version:
$Revision: 1.18 $ $Date: 2004/05/26 21:56:05 $
Author:
Stephen Colebourne
Since:
Commons Collections 3.0

Constructor Summary

Flat3Map()
Constructor.
Flat3Map(Map map)
Constructor copying elements from another map.

Method Summary

void
clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
Object
clone()
Clones the map without cloning the keys or values.
boolean
containsKey(Object key)
Checks whether the map contains the specified key.
boolean
containsValue(Object value)
Checks whether the map contains the specified value.
protected AbstractHashedMap
createDelegateMap()
Create an instance of the map used for storage when in delegation mode.
Set
entrySet()
Gets the entrySet view of the map.
boolean
equals(Object obj)
Compares this map with another.
Object
get(Object key)
Gets the value mapped to the key specified.
int
hashCode()
Gets the standard Map hashCode.
boolean
isEmpty()
Checks whether the map is currently empty.
Set
keySet()
Gets the keySet view of the map.
MapIterator
mapIterator()
Gets an iterator over the map.
Object
put(Object key, Object value)
Puts a key-value mapping into this map.
void
putAll(Map map)
Puts all the values from the specified map into this map.
Object
remove(Object key)
Removes the specified mapping from this map.
int
size()
Gets the size of the map.
String
toString()
Gets the map as a String.
Collection
values()
Gets the values view of the map.

Constructor Details

Flat3Map

public Flat3Map()
Constructor.

Flat3Map

public Flat3Map(Map map)
Constructor copying elements from another map.
Parameters:
map - the map to copy

Method Details

clear

public void clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.

clone

public Object clone()
Clones the map without cloning the keys or values.
Returns:
a shallow clone
Since:
Commons Collections 3.1

containsKey

public boolean containsKey(Object key)
Checks whether the map contains the specified key.
Parameters:
key - the key to search for
Returns:
true if the map contains the key

containsValue

public boolean containsValue(Object value)
Checks whether the map contains the specified value.
Parameters:
value - the value to search for
Returns:
true if the map contains the key

createDelegateMap

protected AbstractHashedMap createDelegateMap()
Create an instance of the map used for storage when in delegation mode.

This can be overridden by subclasses to provide a different map implementation. Not every AbstractHashedMap is suitable, identity and reference based maps would be poor choices.

Returns:
a new AbstractHashedMap or subclass
Since:
Commons Collections 3.1

entrySet

public Set entrySet()
Returns:
the entrySet view

equals

public boolean equals(Object obj)
Compares this map with another.
Parameters:
obj - the object to compare to
Returns:
true if equal

get

public Object get(Object key)
Gets the value mapped to the key specified.
Parameters:
key - the key
Returns:
the mapped value, null if no match

hashCode

public int hashCode()
Gets the standard Map hashCode.
Returns:
the hash code defined in the Map interface

isEmpty

public boolean isEmpty()
Checks whether the map is currently empty.
Returns:
true if the map is currently size zero

keySet

public Set keySet()
Returns:
the keySet view

mapIterator

public MapIterator mapIterator()
Gets an iterator over the map. Changes made to the iterator affect this map.

A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map Entry object.

Specified by:
mapIterator in interface IterableMap
Returns:
the map iterator

put

public Object put(Object key,
                  Object value)
Puts a key-value mapping into this map.
Parameters:
key - the key to add
value - the value to add
Returns:
the value previously mapped to this key, null if none

putAll

public void putAll(Map map)
Puts all the values from the specified map into this map.
Parameters:
map - the map to add

remove

public Object remove(Object key)
Removes the specified mapping from this map.
Parameters:
key - the mapping to remove
Returns:
the value mapped to the removed key, null if key not in map

size

public int size()
Gets the size of the map.
Returns:
the size

toString

public String toString()
Gets the map as a String.
Returns:
a string version of the map

values

public Collection values()
Returns:
the values view

Copyright © 2001-2006 Apache Software Foundation. All Rights Reserved.