A
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.
This map is similar to
ReferenceIdentityMap
.
It differs in that keys and values in this class are compared using
equals()
.
This
Map
implementation does
not allow null elements.
Attempting to add a null key or value to the map will raise a
NullPointerException
.
This implementation is not synchronized.
You can use
java.util.Collections.synchronizedMap
to
provide synchronized access to a
ReferenceMap
.
Remember that synchronization will not stop the garbage collecter removing entries.
All the available iterators can be reset back to the start by casting to
ResettableIterator
and calling
reset()
.
NOTE: As from Commons Collections 3.1 this map extends
AbstractReferenceMap
(previously it extended AbstractMap). As a result, the implementation is now
extensible and provides a
MapIterator
.
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 ReferenceMap
, ReferenceMap
, ReferenceMap
valueType
- the type of reference to use for values;
must be ReferenceMap
, ReferenceMap
, ReferenceMap
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 ReferenceMap
, ReferenceMap
, ReferenceMap
valueType
- the type of reference to use for values;
must be ReferenceMap
, ReferenceMap
, ReferenceMap
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 ReferenceMap
, ReferenceMap
, ReferenceMap
valueType
- the type of reference to use for values;
must be ReferenceMap
, ReferenceMap
, ReferenceMap
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 ReferenceMap
, ReferenceMap
, ReferenceMap
valueType
- the type of reference to use for values;
must be ReferenceMap
, ReferenceMap
, ReferenceMap
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