org.apache.commons.collections
Class FastTreeMap

java.lang.Object
  |
  +--java.util.AbstractMap
        |
        +--java.util.TreeMap
              |
              +--org.apache.commons.collections.FastTreeMap

public class FastTreeMap

extends TreeMap

A customized implementation of java.util.TreeMap designed to operate in a multithreaded environment where the large majority of method calls are read-only, instead of structural changes. When operating in "fast" mode, read calls are non-synchronized and write calls perform the following steps:

• Clone the existing collection
• Perform the modification on the clone
• Replace the existing collection with the (modified) clone

When first created, objects of this class default to "slow" mode, where all accesses of any type are synchronized but no cloning takes place. This is appropriate for initially populating the collection, followed by a switch to "fast" mode (by calling setFast(true)) after initialization is complete.

NOTE: If you are creating and accessing a TreeMap only within a single thread, you should use java.util.TreeMap directly (with no synchronization), for maximum performance.

NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declartion.

Since:

1.0

Version:

$Revision: 1.10 $ $Date: 2002/10/12 22:15:18 $

Author:

Craig R. McClanahan

See Also:

Serialized Form

Field Summary

protected boolean	fast Are we operating in "fast" mode?
protected TreeMap	map The underlying map we are managing.

Constructor Summary

FastTreeMap()
Construct a an empty map.

FastTreeMap(Comparator comparator)
Construct an empty map with the specified comparator.

FastTreeMap(Map map)
Construct a new map with the same mappings as the specified map, sorted according to the keys's natural order

FastTreeMap(SortedMap map)
Construct a new map with the same mappings as the specified map, sorted according to the same ordering

Method Summary

void	clear() Remove all mappings from this map.
Object	clone() Return a shallow copy of this FastTreeMap instance.
Comparator	comparator() Return the comparator used to order this map, or null if this map uses its keys' natural order.
boolean	containsKey(Object key) Return true if this map contains a mapping for the specified key.
boolean	containsValue(Object value) Return true if this map contains one or more keys mapping to the specified value.
Set	entrySet() Return a collection view of the mappings contained in this map.
boolean	equals(Object o) Compare the specified object with this list for equality.
Object	firstKey() Return the first (lowest) key currently in this sorted map.
Object	get(Object key) Return the value to which this map maps the specified key.
boolean	getFast() Returns true if this map is operating in fast mode.
int	hashCode() Return the hash code value for this map.
SortedMap	headMap(Object key) Return a view of the portion of this map whose keys are strictly less than the specified key.
boolean	isEmpty() Test if this list has no elements.
Set	keySet() Return a set view of the keys contained in this map.
Object	lastKey() Return the last (highest) key currently in this sorted map.
Object	put(Object key, Object value) Associate the specified value with the specified key in this map.
void	putAll(Map in) Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.
Object	remove(Object key) Remove any mapping for this key, and return any previously mapped value.
void	setFast(boolean fast) Sets whether this map is operating in fast mode.
int	size() Return the number of key-value mappings in this map.
SortedMap	subMap(Object fromKey, Object toKey) Return a view of the portion of this map whose keys are in the range fromKey (inclusive) to toKey (exclusive).
SortedMap	tailMap(Object key) Return a view of the portion of this map whose keys are greater than or equal to the specified key.
Collection	values() Return a collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap

toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

map

protected TreeMap map

The underlying map we are managing.

fast

protected boolean fast

Are we operating in "fast" mode?

Constructor Detail

FastTreeMap

public FastTreeMap()

Construct a an empty map.

FastTreeMap

public FastTreeMap(Comparator comparator)

Construct an empty map with the specified comparator.

Parameters:

comparator - The comparator to use for ordering tree elements

FastTreeMap

public FastTreeMap(Map map)

Construct a new map with the same mappings as the specified map, sorted according to the keys's natural order

Parameters:

map - The map whose mappings are to be copied

FastTreeMap

public FastTreeMap(SortedMap map)

Construct a new map with the same mappings as the specified map, sorted according to the same ordering

Parameters:

map - The map whose mappings are to be copied

Method Detail

getFast

public boolean getFast()

Returns true if this map is operating in fast mode.

Returns:

true if this map is operating in fast mode

setFast

public void setFast(boolean fast)

Sets whether this map is operating in fast mode.

Parameters:

fast - true if this map should operate in fast mode

clear

public void clear()

Remove all mappings from this map.

Overrides:

clear in class TreeMap

clone

public Object clone()

Return a shallow copy of this FastTreeMap instance. The keys and values themselves are not copied.

Overrides:

clone in class TreeMap

comparator

public Comparator comparator()

Return the comparator used to order this map, or null if this map uses its keys' natural order.

Overrides:

comparator in class TreeMap

containsKey

public boolean containsKey(Object key)

Return true if this map contains a mapping for the specified key.

Overrides:

containsKey in class TreeMap

Parameters:

key - Key to be searched for

containsValue

public boolean containsValue(Object value)

Return true if this map contains one or more keys mapping to the specified value.

Overrides:

containsValue in class TreeMap

Parameters:

value - Value to be searched for

entrySet

public Set entrySet()

Return a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry.

Overrides:

entrySet in class TreeMap

equals

public boolean equals(Object o)

Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for the Map.equals method.

Overrides:

equals in class AbstractMap

Parameters:

o - Object to be compared to this list

firstKey

public Object firstKey()

Return the first (lowest) key currently in this sorted map.

Overrides:

firstKey in class TreeMap

get

public Object get(Object key)

Return the value to which this map maps the specified key. Returns null if the map contains no mapping for this key, or if there is a mapping with a value of null. Use the containsKey() method to disambiguate these cases.

Overrides:

get in class TreeMap

Parameters:

key - Key whose value is to be returned

hashCode

public int hashCode()

Return the hash code value for this map. This implementation uses exactly the code that is used to define the list hash function in the documentation for the Map.hashCode method.

Overrides:

hashCode in class AbstractMap

headMap

public SortedMap headMap(Object key)

Return a view of the portion of this map whose keys are strictly less than the specified key.

Overrides:

headMap in class TreeMap

Parameters:

key - Key higher than any in the returned map

isEmpty

public boolean isEmpty()

Test if this list has no elements.

Overrides:

isEmpty in class AbstractMap

keySet

public Set keySet()

Return a set view of the keys contained in this map.

Overrides:

keySet in class TreeMap

lastKey

public Object lastKey()

Return the last (highest) key currently in this sorted map.

Overrides:

lastKey in class TreeMap

put

public Object put(Object key,
                  Object value)

Associate the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced and returned.

Overrides:

put in class TreeMap

Parameters:

key - The key with which the value is to be associated

value - The value to be associated with this key

putAll

public void putAll(Map in)

Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.

Overrides:

putAll in class TreeMap

Parameters:

in - Map whose mappings are to be copied

remove

public Object remove(Object key)

Remove any mapping for this key, and return any previously mapped value.

Overrides:

remove in class TreeMap

Parameters:

key - Key whose mapping is to be removed

size

public int size()

Return the number of key-value mappings in this map.

Overrides:

size in class TreeMap

subMap

public SortedMap subMap(Object fromKey,
                        Object toKey)

Return a view of the portion of this map whose keys are in the range fromKey (inclusive) to toKey (exclusive).

Overrides:

subMap in class TreeMap

Parameters:

fromKey - Lower limit of keys for the returned map

toKey - Upper limit of keys for the returned map

tailMap

public SortedMap tailMap(Object key)

Return a view of the portion of this map whose keys are greater than or equal to the specified key.

Overrides:

tailMap in class TreeMap

Parameters:

key - Key less than or equal to any in the returned map

values

public Collection values()

Return a collection view of the values contained in this map.

Overrides:

values in class TreeMap