org.apache.commons.collections

Class 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:

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 Declaration.

Version:
$Revision: 1.16 $ $Date: 2004/02/18 01:15:42 $
Authors:
Craig R. McClanahan
Stephen Colebourne
Since:
Commons Collections 1.0

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()
Return true if this map contains no mappings.
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.

Field Details

fast

protected boolean fast
Are we operating in "fast" mode?

map

protected TreeMap map
The underlying map we are managing.

Constructor Details

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 Details

clear

public void clear()
Remove all mappings from this map.

clone

public Object clone()
Return a shallow copy of this FastTreeMap instance. The keys and values themselves are not copied.
Returns:
a clone of this map

comparator

public Comparator comparator()
Return the comparator used to order this map, or null if this map uses its keys' natural order.
Returns:
the comparator used to order the map, or null if natural order

containsKey

public boolean containsKey(Object key)
Return true if this map contains a mapping for the specified key.
Parameters:
key - the key to be searched for
Returns:
true if the map contains the key

containsValue

public boolean containsValue(Object value)
Return true if this map contains one or more keys mapping to the specified value.
Parameters:
value - the value to be searched for
Returns:
true if the map contains the value

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.

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.
Parameters:
o - the object to be compared to this list
Returns:
true if the two maps are equal

firstKey

public Object firstKey()
Return the first (lowest) key currently in this sorted map.
Returns:
the first key in the map

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.
Parameters:
key - the key whose value is to be returned
Returns:
the value mapped to that key, or null

getFast

public boolean getFast()
Returns true if this map is operating in fast mode.
Returns:
true if this map is operating in fast mode

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.
Returns:
a suitable integer hash code

headMap

public SortedMap headMap(Object key)
Return a view of the portion of this map whose keys are strictly less than the specified key.
Parameters:
key - Key higher than any in the returned map
Returns:
a head map

isEmpty

public boolean isEmpty()
Return true if this map contains no mappings.
Returns:
is the map currently empty

keySet

public Set keySet()
Return a set view of the keys contained in this map.

lastKey

public Object lastKey()
Return the last (highest) key currently in this sorted map.
Returns:
the last key in the map

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.
Parameters:
key - the key with which the value is to be associated
value - the value to be associated with this key
Returns:
the value previously mapped to the key, or null

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.
Parameters:
in - the 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.
Parameters:
key - the key whose mapping is to be removed
Returns:
the value removed, or null

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

size

public int size()
Return the number of key-value mappings in this map.
Returns:
the current size of the map

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).
Parameters:
fromKey - Lower limit of keys for the returned map
toKey - Upper limit of keys for the returned map
Returns:
a sub 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.
Parameters:
key - Key less than or equal to any in the returned map
Returns:
a tail map

values

public Collection values()
Return a collection view of the values contained in this map.

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