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org.apache.commons.collections4.map
Class Flat3Map<K,V>

java.lang.Object
  extended by org.apache.commons.collections4.map.Flat3Map<K,V>
All Implemented Interfaces:
Serializable, Cloneable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>
public class Flat3Map<K,V>
extends Object
implements IterableMap<K,V>, 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.

Note that Flat3Map is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
3.0
Version:
$Id: Flat3Map.java 1477799 2013-04-30 19:56:11Z tn $
See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>
 
Constructor Summary
Flat3Map()
          Constructor.
Flat3Map(Map<? extends K,? extends V> 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.
 Flat3Map<K,V> 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<K,V> createDelegateMap()
          Create an instance of the map used for storage when in delegation mode.
 Set<Map.Entry<K,V>> entrySet()
          Gets the entrySet view of the map.
 boolean equals(Object obj)
          Compares this map with another.
 V 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<K> keySet()
          Gets the keySet view of the map.
 MapIterator<K,V> mapIterator()
          Gets an iterator over the map.
 V put(K key, V value)
          Puts a key-value mapping into this map.
 void putAll(Map<? extends K,? extends V> map)
          Puts all the values from the specified map into this map.
 V 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<V> values()
          Gets the values view of the map.
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Flat3Map

public Flat3Map()
Constructor.

Flat3Map

public Flat3Map(Map<? extends K,? extends V> map)
Constructor copying elements from another map.

Parameters:
map - the map to copy
Throws:
NullPointerException - if the map is null
Method Detail

get

public V get(Object key)
Gets the value mapped to the key specified.

Specified by:
get in interface Map<K,V>
Specified by:
get in interface Get<K,V>
Parameters:
key - the key
Returns:
the mapped value, null if no match
See Also:
Map.get(Object)

size

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

Specified by:
size in interface Map<K,V>
Specified by:
size in interface Get<K,V>
Returns:
the size
See Also:
Map.size()

isEmpty

public boolean isEmpty()
Checks whether the map is currently empty.

Specified by:
isEmpty in interface Map<K,V>
Specified by:
isEmpty in interface Get<K,V>
Returns:
true if the map is currently size zero
See Also:
Map.isEmpty()

containsKey

public boolean containsKey(Object key)
Checks whether the map contains the specified key.

Specified by:
containsKey in interface Map<K,V>
Specified by:
containsKey in interface Get<K,V>
Parameters:
key - the key to search for
Returns:
true if the map contains the key
See Also:
Map.containsKey(Object)

containsValue

public boolean containsValue(Object value)
Checks whether the map contains the specified value.

Specified by:
containsValue in interface Map<K,V>
Specified by:
containsValue in interface Get<K,V>
Parameters:
value - the value to search for
Returns:
true if the map contains the key
See Also:
Map.containsValue(Object)

put

public V put(K key,
             V value)
Puts a key-value mapping into this map.

Specified by:
put in interface Map<K,V>
Specified by:
put in interface Put<K,V>
Parameters:
key - the key to add
value - the value to add
Returns:
the value previously mapped to this key, null if none
See Also:
Map.put(Object, Object)

putAll

public void putAll(Map<? extends K,? extends V> map)
Puts all the values from the specified map into this map.

Specified by:
putAll in interface Map<K,V>
Specified by:
putAll in interface Put<K,V>
Parameters:
map - the map to add
Throws:
NullPointerException - if the map is null
See Also:
Map.putAll(Map)

createDelegateMap

protected AbstractHashedMap<K,V> 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:
3.1

remove

public V remove(Object key)
Removes the specified mapping from this map.

Specified by:
remove in interface Map<K,V>
Specified by:
remove in interface Get<K,V>
Parameters:
key - the mapping to remove
Returns:
the value mapped to the removed key, null if key not in map
See Also:
Map.remove(Object)

clear

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

Specified by:
clear in interface Map<K,V>
Specified by:
clear in interface Put<K,V>
See Also:
Map.clear()

mapIterator

public MapIterator<K,V> 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 IterableGet<K,V>
Returns:
the map iterator

entrySet

public Set<Map.Entry<K,V>> entrySet()
Gets the entrySet view of the map. Changes made to the view affect this map.

NOTE: from 4.0, the returned Map Entry will be an independent object and will not change anymore as the iterator progresses. To avoid this additional object creation and simply iterate through the entries, use mapIterator().

Specified by:
entrySet in interface Map<K,V>
Specified by:
entrySet in interface Get<K,V>
Returns:
the entrySet view
See Also:
Map.entrySet()

keySet

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

Specified by:
keySet in interface Map<K,V>
Specified by:
keySet in interface Get<K,V>
Returns:
the keySet view
See Also:
Map.keySet()

values

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

Specified by:
values in interface Map<K,V>
Specified by:
values in interface Get<K,V>
Returns:
the values view
See Also:
Map.values()

clone

public Flat3Map<K,V> clone()
Clones the map without cloning the keys or values.

Overrides:
clone in class Object
Returns:
a shallow clone
Since:
3.1

equals

public boolean equals(Object obj)
Compares this map with another.

Specified by:
equals in interface Map<K,V>
Overrides:
equals in class Object
Parameters:
obj - the object to compare to
Returns:
true if equal

hashCode

public int hashCode()
Gets the standard Map hashCode.

Specified by:
hashCode in interface Map<K,V>
Overrides:
hashCode in class Object
Returns:
the hash code defined in the Map interface

toString

public String toString()
Gets the map as a String.

Overrides:
toString in class Object
Returns:
a string version of the map
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