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org.apache.commons.collections.map

Class Flat3Map

java.lang.Object
|
+--org.apache.commons.collections.map.Flat3Map

All Implemented Interfaces:
IterableMap


public class Flat3Map
extends java.lang.Object
implements IterableMap

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.

Since:
Commons Collections 3.0
Author:
Stephen Colebourne

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.

boolean

containsKey(Object key)

Checks whether the map contains the specified key.

boolean

containsValue(Object value)

Checks whether the map contains the specified value.

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.


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

entrySet

public Set entrySet()

Gets the entrySet view of the map. Changes made to the view affect this map. The Map Entry is not an independent object and changes as the iterator progresses. To simply iterate through the entries, use mapIterator().

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()

Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator().

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.

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 -

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()

Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, use mapIterator().

Returns:
the values view