org.apache.commons.collections.map
public class ReferenceIdentityMap extends AbstractReferenceMap implements Serializable
Map
implementation that allows mappings to be
removed by the garbage collector and matches keys and values based
on ==
not equals()
.
When you construct a ReferenceIdentityMap
, 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 default constructor uses hard keys and soft values, providing a memory-sensitive cache.
This map is similar to
ReferenceMap
.
It differs in that keys and values in this class are compared using ==
.
This map will violate the detail of various Map and map view contracts. As a general rule, don't compare this map to other maps.
This java.util.Map 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 ReferenceIdentityMap
.
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 that ReferenceIdentityMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using java.util.Collections#synchronizedMap. This class may throw exceptions when accessed by concurrent threads without synchronization.
Since: Commons Collections 3.0 (previously in main package v2.1)
Version: $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
See Also: java.lang.ref.Reference
Constructor Summary | |
---|---|
ReferenceIdentityMap()
Constructs a new ReferenceIdentityMap that will
use hard references to keys and soft references to values. | |
ReferenceIdentityMap(int keyType, int valueType)
Constructs a new ReferenceIdentityMap that will
use the specified types of references.
| |
ReferenceIdentityMap(int keyType, int valueType, boolean purgeValues)
Constructs a new ReferenceIdentityMap that will
use the specified types of references.
| |
ReferenceIdentityMap(int keyType, int valueType, int capacity, float loadFactor)
Constructs a new ReferenceIdentityMap with the
specified reference types, load factor and initial capacity.
| |
ReferenceIdentityMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues)
Constructs a new ReferenceIdentityMap with the
specified reference types, load factor and initial capacity.
|
Method Summary | |
---|---|
protected int | hash(Object key)
Gets the hash code for the key specified.
|
protected int | hashEntry(Object key, Object value)
Gets the hash code for a MapEntry.
|
protected boolean | isEqualKey(Object key1, Object key2)
Compares two keys for equals.
|
protected boolean | isEqualValue(Object value1, Object value2)
Compares two values for equals.
|
ReferenceIdentityMap
that will
use hard references to keys and soft references to values.ReferenceIdentityMap
that will
use the specified types of references.
Parameters: keyType the type of reference to use for keys; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap valueType the type of reference to use for values; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap
ReferenceIdentityMap
that will
use the specified types of references.
Parameters: keyType the type of reference to use for keys; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap valueType the type of reference to use for values; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap purgeValues should the value be automatically purged when the key is garbage collected
ReferenceIdentityMap
with the
specified reference types, load factor and initial capacity.
Parameters: keyType the type of reference to use for keys; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap valueType the type of reference to use for values; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap capacity the initial capacity for the map loadFactor the load factor for the map
ReferenceIdentityMap
with the
specified reference types, load factor and initial capacity.
Parameters: keyType the type of reference to use for keys; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap valueType the type of reference to use for values; must be ReferenceIdentityMap, ReferenceIdentityMap, ReferenceIdentityMap 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
This implementation uses the identity hash code.
Parameters: key the key to get a hash code for
Returns: the hash code
This implementation uses the identity hash code.
Parameters: key the key to get a hash code for, may be null value the value to get a hash code for, may be null
Returns: the hash code, as per the MapEntry specification
This implementation converts the key from the entry to a real reference
before comparison and uses ==
.
Parameters: key1 the first key to compare passed in from outside key2 the second key extracted from the entry via entry.key
Returns: true if equal by identity
This implementation uses ==
.
Parameters: value1 the first value to compare passed in from outside value2 the second value extracted from the entry via getValue()
Returns: true if equal by identity