org.apache.commons.collections
public class ReferenceMap extends AbstractMap
Deprecated: Moved to map subpackage. Due to be removed in v4.0.
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
.
Since: Commons Collections 2.1
Version: $Revision: 348444 $ $Date: 2005-11-23 14:06:56 +0000 (Wed, 23 Nov 2005) $
See Also: java.lang.ref.Reference
Field Summary | |
---|---|
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. |
Constructor Summary | |
---|---|
ReferenceMap()
Constructs a new ReferenceMap that will
use hard references to keys and soft references to values. | |
ReferenceMap(int keyType, int valueType, boolean purgeValues)
Constructs a new ReferenceMap that will
use the specified types of references.
| |
ReferenceMap(int keyType, int valueType)
Constructs a new ReferenceMap that will
use the specified types of references.
| |
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.
| |
ReferenceMap(int keyType, int valueType, int capacity, float loadFactor)
Constructs a new ReferenceMap with the
specified reference types, load factor and initial
capacity.
|
Method Summary | |
---|---|
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. Neither the key nor the value may be null. |
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.
|
ReferenceMap
that will
use hard references to keys and soft references to values.ReferenceMap
that will
use the specified types of references.
Parameters: 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
that will
use the specified types of references.
Parameters: 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
with the
specified reference types, load factor and initial
capacity.
Parameters: 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 map loadFactor the load factor for the map purgeValues should the value be automatically purged when the key is garbage collected
ReferenceMap
with the
specified reference types, load factor and initial
capacity.
Parameters: 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 map loadFactor the load factor for the map
true
if this map contains the given key.
Returns: true if the given key is in this map
Returns: a set view of this map's entries
Returns: the value associated with the given key, or null
if the key maps to no value
true
if this map is empty.
Returns: true
if this map is empty
Returns: a set view of this map's keys
Neither the key nor the value may be null.
Parameters: key the key of the mapping value the value of the mapping
Returns: the last value associated with that key, or null if no value was associated with the key
Throws: NullPointerException if either the key or value is null
Parameters: key the key to remove
Returns: the value associated with that key, or null if the key was not in the map
Returns: the size of this map
Returns: a collection view of this map's values.