| java.lang.Object
 org.apache.commons.collections.map.Flat3Map
| Flat3Map | | public class Flat3Map implements IterableMap,Serializable,Cloneable(Code) | | 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.
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
java.util.Collections.synchronizedMap(Map) . This class may throw
exceptions when accessed by concurrent threads without synchronization.
since:
Commons Collections 3.0
version:
$Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
author:
Stephen Colebourne |
| Inner Class :static class KeySetIterator extends EntrySetIterator | |
| Inner Class :static class ValuesIterator extends EntrySetIterator | |
| Constructor Summary | |
| public | Flat3Map()
Constructor. | | public | Flat3Map(Map map)
Constructor copying elements from another map. |
| Method Summary | |
| public void | clear()
Clears the map, resetting the size to zero and nullifying references
to avoid garbage collection issues. | | public Object | clone()
Clones the map without cloning the keys or values. | | public boolean | containsKey(Object key)
Checks whether the map contains the specified key. | | public 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. | | public Set | entrySet()
Gets the entrySet view of the map. | | public boolean | equals(Object obj)
Compares this map with another. | | public Object | get(Object key)
Gets the value mapped to the key specified. | | public int | hashCode()
Gets the standard Map hashCode. | | public boolean | isEmpty()
Checks whether the map is currently empty. | | public Set | keySet()
Gets the keySet view of the map. | | 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. | | public Object | put(Object key, Object value)
Puts a key-value mapping into this map. | | public void | putAll(Map map)
Puts all the values from the specified map into this map. | | public Object | remove(Object key)
Removes the specified mapping from this map. | | public int | size()
Gets the size of the map. | | public String | toString()
Gets the map as a String. | | public Collection | values()
Gets the values view of the map. |
| Flat3Map | | public Flat3Map()(Code) | | Constructor.
|
| Flat3Map | | public Flat3Map(Map map)(Code) | | Constructor copying elements from another map.
Parameters:
map - the map to copy
throws:
NullPointerException - if the map is null |
| clear | | public void clear()(Code) | | Clears the map, resetting the size to zero and nullifying references
to avoid garbage collection issues.
|
| clone | | public Object clone()(Code) | | Clones the map without cloning the keys or values.
a shallow clone
since:
Commons Collections 3.1 |
| containsKey | | public boolean containsKey(Object key)(Code) | | Checks whether the map contains the specified key.
Parameters:
key - the key to search for true if the map contains the key |
| containsValue | | public boolean containsValue(Object value)(Code) | | Checks whether the map contains the specified value.
Parameters:
value - the value to search for true if the map contains the key |
| createDelegateMap | | protected AbstractHashedMap createDelegateMap()(Code) | | 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
since:
Commons Collections 3.1 |
| entrySet | | public Set entrySet()(Code) | | 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
Flat3Map.mapIterator() .
the entrySet view |
| equals | | public boolean equals(Object obj)(Code) | | Compares this map with another.
Parameters:
obj - the object to compare to true if equal |
| get | | public Object get(Object key)(Code) | | Gets the value mapped to the key specified.
Parameters:
key - the key the mapped value, null if no match |
| hashCode | | public int hashCode()(Code) | | Gets the standard Map hashCode.
the hash code defined in the Map interface |
| isEmpty | | public boolean isEmpty()(Code) | | Checks whether the map is currently empty.
true if the map is currently size zero |
| keySet | | public Set keySet()(Code) | | Gets the keySet view of the map.
Changes made to the view affect this map.
To simply iterate through the keys, use
Flat3Map.mapIterator() .
the keySet view |
| mapIterator | | public MapIterator mapIterator()(Code) | | 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.
the map iterator |
| put | | public Object put(Object key, Object value)(Code) | | Puts a key-value mapping into this map.
Parameters:
key - the key to add
Parameters:
value - the value to add the value previously mapped to this key, null if none |
| putAll | | public void putAll(Map map)(Code) | | Puts all the values from the specified map into this map.
Parameters:
map - the map to add
throws:
NullPointerException - if the map is null |
| remove | | public Object remove(Object key)(Code) | | Removes the specified mapping from this map.
Parameters:
key - the mapping to remove the value mapped to the removed key, null if key not in map |
| size | | public int size()(Code) | | Gets the size of the map.
the size |
| toString | | public String toString()(Code) | | Gets the map as a String.
a string version of the map |
| values | | public Collection values()(Code) | | Gets the values view of the map.
Changes made to the view affect this map.
To simply iterate through the values, use
Flat3Map.mapIterator() .
the values view |
|
|