org.apache.commons.collections
Class ReferenceMap
AbstractMap
org.apache.commons.collections.ReferenceMap
public class ReferenceMap
extends AbstractMap
Hash-based
Map
implementation that allows
mappings to be removed by the garbage collector.
When you construct a
ReferenceMap
, you can
specify what kind of references are used to store the
map's keys and values. If non-hard references are
used, then the garbage collector can remove mappings
if a key or value becomes unreachable, or if the
JVM's memory is running low. For information on how
the different reference types behave, see
Reference
.
Different types of references can be specified for keys
and values. The keys can be configured to be weak but
the values hard, in which case this class will behave
like a
WeakHashMap
. However, you
can also specify hard keys and weak values, or any other
combination. The default constructor uses hard keys
and soft values, providing a memory-sensitive cache.
The algorithms used are basically the same as those
in
java.util.HashMap
. In particular, you
can specify a load factor and capacity to suit your
needs. All optional
Map
operations are
supported.
However, this
Map
implementation does
not
allow null elements. Attempting to add a null key or
or a null value to the map will raise a
NullPointerException
.
As usual, this implementation is not synchronized. You
can use
java.util.Collections.synchronizedMap
to
provide synchronized access to a
ReferenceMap
.
$Revision: 1.22 $ $Date: 2004/02/18 01:15:42 $static int | HARD - Constant indicating that hard references should be used.
|
static int | SOFT - Constant indicating that soft references should be used.
|
static int | WEAK - Constant indicating that weak references should be used.
|
ReferenceMap() - Constructs a new
ReferenceMap that will
use hard references to keys and soft references to values.
|
ReferenceMap(int keyType, int valueType) - Constructs a new
ReferenceMap that will
use the specified types of references.
|
ReferenceMap(int keyType, int valueType, boolean purgeValues) - Constructs a new
ReferenceMap that will
use the specified types of references.
|
ReferenceMap(int keyType, int valueType, int capacity, float loadFactor) - Constructs a new
ReferenceMap with the
specified reference types, load factor and initial
capacity.
|
ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues) - Constructs a new
ReferenceMap with the
specified reference types, load factor and initial
capacity.
|
void | clear() - Clears this map.
|
boolean | containsKey(Object key) - Returns
true if this map contains the given key.
|
Set | entrySet() - Returns a set view of this map's entries.
|
Object | get(Object key) - Returns the value associated with the given key, if any.
|
boolean | isEmpty() - Returns
true if this map is empty.
|
Set | keySet() - Returns a set view of this map's keys.
|
Object | put(Object key, Object value) - Associates the given key with the given value.
|
Object | remove(Object key) - Removes the key and its associated value from this map.
|
int | size() - Returns the size of this map.
|
Collection | values() - Returns a collection view of this map's values.
|
HARD
public static final int HARD
Constant indicating that hard references should be used.
SOFT
public static final int SOFT
Constant indicating that soft references should be used.
WEAK
public static final int WEAK
Constant indicating that weak references should be used.
ReferenceMap
public ReferenceMap()
Constructs a new ReferenceMap
that will
use hard references to keys and soft references to values.
ReferenceMap
public ReferenceMap(int keyType,
int valueType)
Constructs a new ReferenceMap
that will
use the specified types of references.
keyType
- the type of reference to use for keys;
must be HARD
, SOFT
, WEAK
valueType
- the type of reference to use for values;
must be HARD
, SOFT
, WEAK
ReferenceMap
public ReferenceMap(int keyType,
int valueType,
boolean purgeValues)
Constructs a new ReferenceMap
that will
use the specified types of references.
keyType
- the type of reference to use for keys;
must be HARD
, SOFT
, WEAK
valueType
- the type of reference to use for values;
must be HARD
, SOFT
, WEAK
purgeValues
- should the value be automatically purged when the
key is garbage collected
ReferenceMap
public ReferenceMap(int keyType,
int valueType,
int capacity,
float loadFactor)
Constructs a new ReferenceMap
with the
specified reference types, load factor and initial
capacity.
keyType
- the type of reference to use for keys;
must be HARD
, SOFT
, WEAK
valueType
- the type of reference to use for values;
must be HARD
, SOFT
, WEAK
capacity
- the initial capacity for the maploadFactor
- the load factor for the map
ReferenceMap
public ReferenceMap(int keyType,
int valueType,
int capacity,
float loadFactor,
boolean purgeValues)
Constructs a new ReferenceMap
with the
specified reference types, load factor and initial
capacity.
keyType
- the type of reference to use for keys;
must be HARD
, SOFT
, WEAK
valueType
- the type of reference to use for values;
must be HARD
, SOFT
, WEAK
capacity
- the initial capacity for the maploadFactor
- the load factor for the mappurgeValues
- should the value be automatically purged when the
key is garbage collected
clear
public void clear()
Clears this map.
containsKey
public boolean containsKey(Object key)
Returns true
if this map contains the given key.
- true if the given key is in this map
entrySet
public Set entrySet()
Returns a set view of this map's entries.
- a set view of this map's entries
get
public Object get(Object key)
Returns the value associated with the given key, if any.
- the value associated with the given key, or
null
if the key maps to no value
isEmpty
public boolean isEmpty()
Returns true
if this map is empty.
true
if this map is empty
keySet
public Set keySet()
Returns a set view of this map's keys.
- a set view of this map's keys
put
public Object put(Object key,
Object value)
Associates the given key with the given value.
Neither the key nor the value may be null.
key
- the key of the mappingvalue
- the value of the mapping
- the last value associated with that key, or
null if no value was associated with the key
remove
public Object remove(Object key)
Removes the key and its associated value from this map.
- the value associated with that key, or null if
the key was not in the map
size
public int size()
Returns the size of this map.
values
public Collection values()
Returns a collection view of this map's values.
- a collection view of this map's values.
Copyright © 2001-2006 Apache Software Foundation. All Rights Reserved.