| java.lang.Object
 java.util.AbstractMap
org.apache.commons.collections.ReferenceMap
| ReferenceMap | | public class ReferenceMap extends AbstractMap (Code) | | 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.
See Also: java.lang.ref.Reference
since:
Commons Collections 2.1
version:
$Revision: 348444 $ $Date: 2005-11-23 14:06:56 +0000 (Wed, 23 Nov 2005) $
author:
Paul Jack |
| Field Summary | |
| final public static int | HARD
Constant indicating that hard references should be used. | | final public static int | SOFT
Constant indicating that soft references should be used. | | final public static int | WEAK
Constant indicating that weak references should be used. |
| Constructor Summary | |
| public | ReferenceMap()
Constructs a new ReferenceMap that will
use hard references to keys and soft references to values. | | public | ReferenceMap(int keyType, int valueType, boolean purgeValues)
Constructs a new ReferenceMap that will
use the specified types of references. | | public | ReferenceMap(int keyType, int valueType)
Constructs a new ReferenceMap that will
use the specified types of references. | | 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. | | public | 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 | |
| public void | clear()
Clears this map. | | public boolean | containsKey(Object key)
Returns true if this map contains the given key. | | public Set | entrySet()
Returns a set view of this map's entries. | | public Object | get(Object key)
Returns the value associated with the given key, if any. | | public boolean | isEmpty()
Returns true if this map is empty. | | public Set | keySet()
Returns a set view of this map's keys. | | public Object | put(Object key, Object value)
Associates the given key with the given value.
Neither the key nor the value may be null. | | public Object | remove(Object key)
Removes the key and its associated value from this map. | | public int | size()
Returns the size of this map. | | public Collection | values()
Returns a collection view of this map's values. |
| HARD | | final public static int HARD(Code) | | Constant indicating that hard references should be used.
|
| SOFT | | final public static int SOFT(Code) | | Constant indicating that soft references should be used.
|
| WEAK | | final public static int WEAK(Code) | | Constant indicating that weak references should be used.
|
| ReferenceMap | | public ReferenceMap()(Code) | | Constructs a new ReferenceMap that will
use hard references to keys and soft references to values.
|
| ReferenceMap | | public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues)(Code) | | Constructs a new ReferenceMap with the
specified reference types, load factor and initial
capacity.
Parameters:
keyType - the type of reference to use for keys;must be ReferenceMap.HARD, ReferenceMap.SOFT, ReferenceMap.WEAK
Parameters:
valueType - the type of reference to use for values;must be ReferenceMap.HARD, ReferenceMap.SOFT, ReferenceMap.WEAK
Parameters:
capacity - the initial capacity for the map
Parameters:
loadFactor - the load factor for the map
Parameters:
purgeValues - should the value be automatically purged when the key is garbage collected |
| ReferenceMap | | public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor)(Code) | | Constructs a new ReferenceMap with the
specified reference types, load factor and initial
capacity.
Parameters:
keyType - the type of reference to use for keys;must be ReferenceMap.HARD, ReferenceMap.SOFT, ReferenceMap.WEAK
Parameters:
valueType - the type of reference to use for values;must be ReferenceMap.HARD, ReferenceMap.SOFT, ReferenceMap.WEAK
Parameters:
capacity - the initial capacity for the map
Parameters:
loadFactor - the load factor for the map |
| clear | | public void clear()(Code) | | Clears this map.
|
| containsKey | | public boolean containsKey(Object key)(Code) | | Returns true if this map contains the given key.
true if the given key is in this map |
| entrySet | | public Set entrySet()(Code) | | Returns a set view of this map's entries.
a set view of this map's entries |
| get | | public Object get(Object key)(Code) | | Returns the value associated with the given key, if any.
the value associated with the given key, or nullif the key maps to no value |
| isEmpty | | public boolean isEmpty()(Code) | | Returns true if this map is empty.
true if this map is empty |
| keySet | | public Set keySet()(Code) | | 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)(Code) | | Associates the given key with the given value.
Neither the key nor the value may be null.
Parameters:
key - the key of the mapping
Parameters:
value - the value of the mapping the last value associated with that key, or null if no value was associated with the key
throws:
NullPointerException - if either the key or valueis null |
| remove | | public Object remove(Object key)(Code) | | Removes the key and its associated value from this map.
Parameters:
key - the key to remove the value associated with that key, or null ifthe key was not in the map |
| size | | public int size()(Code) | | Returns the size of this map.
the size of this map |
| values | | public Collection values()(Code) | | Returns a collection view of this map's values.
a collection view of this map's values. |
|
|