org.apache.commons.collections.map
Class Flat3Map
java.lang.Object
org.apache.commons.collections.map.Flat3Map
- Cloneable, IterableMap, Map, Serializable
public class Flat3Map
extends java.lang.Object
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.
- 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 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.
$Revision: 1.18 $ $Date: 2004/05/26 21:56:05 $Flat3Map() - Constructor.
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Flat3Map(Map map) - Constructor copying elements from another map.
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void | clear() - Clears the map, resetting the size to zero and nullifying references
to avoid garbage collection issues.
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Object | clone() - Clones the map without cloning the keys or values.
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boolean | containsKey(Object key) - Checks whether the map contains the specified key.
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boolean | containsValue(Object value) - Checks whether the map contains the specified value.
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protected AbstractHashedMap | createDelegateMap() - Create an instance of the map used for storage when in delegation mode.
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Set | entrySet() - Gets the entrySet view of the map.
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boolean | equals(Object obj) - Compares this map with another.
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Object | get(Object key) - Gets the value mapped to the key specified.
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int | hashCode() - Gets the standard Map hashCode.
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boolean | isEmpty() - Checks whether the map is currently empty.
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Set | keySet() - Gets the keySet view of the map.
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MapIterator | mapIterator() - Gets an iterator over the map.
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Object | put(Object key, Object value) - Puts a key-value mapping into this map.
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void | putAll(Map map) - Puts all the values from the specified map into this map.
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Object | remove(Object key) - Removes the specified mapping from this map.
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int | size() - Gets the size of the map.
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String | toString() - Gets the map as a String.
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Collection | values() - Gets the values view of the map.
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Flat3Map
public Flat3Map()
Constructor.
Flat3Map
public Flat3Map(Map map)
Constructor copying elements from another map.
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.
containsKey
public boolean containsKey(Object key)
Checks whether the map contains the specified key.
key
- the key to search for
- true if the map contains the key
containsValue
public boolean containsValue(Object value)
Checks whether the map contains the specified value.
value
- the value to search for
- 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.
- a new AbstractHashedMap or subclass
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()
.
equals
public boolean equals(Object obj)
Compares this map with another.
obj
- the object to compare to
get
public Object get(Object key)
Gets the value mapped to the key specified.
- the mapped value, null if no match
hashCode
public int hashCode()
Gets the standard Map hashCode.
- the hash code defined in the Map interface
isEmpty
public boolean isEmpty()
Checks whether the map is currently empty.
- 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()
.
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.
- mapIterator in interface IterableMap
put
public Object put(Object key,
Object value)
Puts a key-value mapping into this map.
key
- the key to addvalue
- the value to add
- 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.
remove
public Object remove(Object key)
Removes the specified mapping from this map.
key
- the mapping to remove
- the value mapped to the removed key, null if key not in map
size
public int size()
Gets the size of the map.
toString
public String toString()
Gets the map as a String.
- 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()
.
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