A
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
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()
.
ReferenceIdentityMap
public ReferenceIdentityMap()
Constructs a new ReferenceIdentityMap
that will
use hard references to keys and soft references to values.
ReferenceIdentityMap
public ReferenceIdentityMap(int keyType,
int valueType)
Constructs a new ReferenceIdentityMap
that will
use the specified types of references.
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
public ReferenceIdentityMap(int keyType,
int valueType,
boolean purgeValues)
Constructs a new ReferenceIdentityMap
that will
use the specified types of references.
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
public ReferenceIdentityMap(int keyType,
int valueType,
int capacity,
float loadFactor)
Constructs a new ReferenceIdentityMap
with the
specified reference types, load factor and initial capacity.
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 maploadFactor
- the load factor for the map
ReferenceIdentityMap
public 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.
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 maploadFactor
- the load factor for the mappurgeValues
- should the value be automatically purged when the
key is garbage collected
hash
protected int hash(Object key)
Gets the hash code for the key specified.
This implementation uses the identity hash code.
- hash in interface AbstractHashedMap
key
- the key to get a hash code for
- the hash code
hashEntry
protected int hashEntry(Object key,
Object value)
Gets the hash code for a MapEntry.
This implementation uses the identity hash code.
- hashEntry in interface AbstractReferenceMap
key
- the key to get a hash code for, may be nullvalue
- the value to get a hash code for, may be null
- the hash code, as per the MapEntry specification
isEqualKey
protected boolean isEqualKey(Object key1,
Object key2)
Compares two keys for equals.
This implementation converts the key from the entry to a real reference
before comparison and uses
==
.
- isEqualKey in interface AbstractReferenceMap
key1
- the first key to compare passed in from outsidekey2
- the second key extracted from the entry via entry.key
- true if equal by identity
isEqualValue
protected boolean isEqualValue(Object value1,
Object value2)
Compares two values for equals.
This implementation uses
==
.
- isEqualValue in interface AbstractHashedMap
value1
- the first value to compare passed in from outsidevalue2
- the second value extracted from the entry via getValue()
- true if equal by identity