Class Flat3Map<K,V>
- java.lang.Object
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- org.apache.commons.collections4.map.Flat3Map<K,V>
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- All Implemented Interfaces:
java.io.Serializable
,java.lang.Cloneable
,java.util.Map<K,V>
,Get<K,V>
,IterableGet<K,V>
,IterableMap<K,V>
,Put<K,V>
public class Flat3Map<K,V> extends java.lang.Object implements IterableMap<K,V>, java.io.Serializable, java.lang.Cloneable
AMap
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.
- Optimised for operation at size 3 or less.
- Still works well once size 3 exceeded.
- Gets at size 3 or less are about 0-10% faster than HashMap,
- Puts at size 3 or less are over 4 times faster than HashMap.
- Performance 5% slower than HashMap once size 3 exceeded once.
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
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description 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(java.lang.Object key)
Checks whether the map contains the specified key.boolean
containsValue(java.lang.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.java.util.Set<java.util.Map.Entry<K,V>>
entrySet()
Gets the entrySet view of the map.boolean
equals(java.lang.Object obj)
Compares this map with another.V
get(java.lang.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.java.util.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(java.util.Map<? extends K,? extends V> map)
Puts all the values from the specified map into this map.V
remove(java.lang.Object key)
Removes the specified mapping from this map.int
size()
Gets the size of the map.java.lang.String
toString()
Gets the map as a String.java.util.Collection<V>
values()
Gets the values view of the map.
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Method Detail
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get
public V get(java.lang.Object key)
Gets the value mapped to the key specified.
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size
public int size()
Gets the size of the map.
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isEmpty
public boolean isEmpty()
Checks whether the map is currently empty.
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containsKey
public boolean containsKey(java.lang.Object key)
Checks whether the map contains the specified key.
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containsValue
public boolean containsValue(java.lang.Object value)
Checks whether the map contains the specified value.
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putAll
public void putAll(java.util.Map<? extends K,? extends V> map)
Puts all the values from the specified map into this map.
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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
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remove
public V remove(java.lang.Object key)
Removes the specified mapping from this map.
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clear
public void clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
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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 interfaceIterableGet<K,V>
- Returns:
- the map iterator
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entrySet
public java.util.Set<java.util.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()
.
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keySet
public java.util.Set<K> keySet()
Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, usemapIterator()
.
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values
public java.util.Collection<V> values()
Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, usemapIterator()
.
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clone
public Flat3Map<K,V> clone()
Clones the map without cloning the keys or values.- Overrides:
clone
in classjava.lang.Object
- Returns:
- a shallow clone
- Since:
- 3.1
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equals
public boolean equals(java.lang.Object obj)
Compares this map with another.
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hashCode
public int hashCode()
Gets the standard Map hashCode.
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toString
public java.lang.String toString()
Gets the map as a String.- Overrides:
toString
in classjava.lang.Object
- Returns:
- a string version of the map
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