Class ReferenceMap
- All Implemented Interfaces:
Map
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 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 Collections.synchronizedMap(java.util.Map<K, V>)
to
provide synchronized access to a ReferenceMap
.
- Since:
- Commons Collections 2.1
- Version:
- $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
- See Also:
-
Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionprivate class
Deprecated.private class
Deprecated.private class
Deprecated.private static class
Deprecated.private class
Deprecated.private static class
Deprecated.Nested classes/interfaces inherited from class java.util.AbstractMap
AbstractMap.SimpleEntry<K extends Object,
V extends Object>, AbstractMap.SimpleImmutableEntry<K extends Object, V extends Object> -
Field Summary
FieldsModifier and TypeFieldDescriptionprivate Set
Deprecated.Cached entry set.static final int
Deprecated.Constant indicating that hard references should be used.private Set
Deprecated.Cached key set.private int
Deprecated.The reference type for keys.private float
Deprecated.The threshold variable is calculated by multiplying table.length and loadFactor.private int
Deprecated.Number of times this map has been modified.private boolean
Deprecated.Should the value be automatically purged when the associated key has been collected?private ReferenceQueue
Deprecated.ReferenceQueue used to eliminate stale mappings.private static final long
Deprecated.For serialization.private int
Deprecated.Number of mappings in this map.static final int
Deprecated.Constant indicating that soft references should be used.private ReferenceMap.Entry[]
Deprecated.The hash table.private int
Deprecated.When size reaches threshold, the map is resized.private Collection
Deprecated.Cached values.private int
Deprecated.The reference type for values.static final int
Deprecated.Constant indicating that weak references should be used. -
Constructor Summary
ConstructorsConstructorDescriptionDeprecated.Constructs a newReferenceMap
that will use hard references to keys and soft references to values.ReferenceMap
(int keyType, int valueType) Deprecated.Constructs a newReferenceMap
that will use the specified types of references.ReferenceMap
(int keyType, int valueType, boolean purgeValues) Deprecated.Constructs a newReferenceMap
that will use the specified types of references.ReferenceMap
(int keyType, int valueType, int capacity, float loadFactor) Deprecated.Constructs a newReferenceMap
with the specified reference types, load factor and initial capacity.ReferenceMap
(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues) Deprecated.Constructs a newReferenceMap
with the specified reference types, load factor and initial capacity. -
Method Summary
Modifier and TypeMethodDescriptionvoid
clear()
Deprecated.Clears this map.boolean
containsKey
(Object key) Deprecated.Returnstrue
if this map contains the given key.entrySet()
Deprecated.Returns a set view of this map's entries.Deprecated.Returns the value associated with the given key, if any.private ReferenceMap.Entry
Deprecated.Returns the entry associated with the given key.private int
indexFor
(int hash) Deprecated.Converts the given hash code into an index into the hash table.boolean
isEmpty()
Deprecated.Returnstrue
if this map is empty.keySet()
Deprecated.Returns a set view of this map's keys.private void
purge()
Deprecated.Purges stale mappings from this map.private void
Deprecated.Deprecated.Associates the given key with the given value.private void
Deprecated.Reads the contents of this object from the given input stream.Deprecated.Removes the key and its associated value from this map.private void
resize()
Deprecated.Resizes this hash table by doubling its capacity.int
size()
Deprecated.Returns the size of this map.private Object
toReference
(int type, Object referent, int hash) Deprecated.Constructs a reference of the given type to the given referent.values()
Deprecated.Returns a collection view of this map's values.private static void
Deprecated.private void
Deprecated.Writes this object to the given output stream.Methods inherited from class java.util.AbstractMap
clone, containsValue, equals, hashCode, putAll, toString
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
-
Field Details
-
serialVersionUID
private static final long serialVersionUIDDeprecated.For serialization.- See Also:
-
HARD
public static final int HARDDeprecated.Constant indicating that hard references should be used.- See Also:
-
SOFT
public static final int SOFTDeprecated.Constant indicating that soft references should be used.- See Also:
-
WEAK
public static final int WEAKDeprecated.Constant indicating that weak references should be used.- See Also:
-
keyType
private int keyTypeDeprecated.The reference type for keys. Must be HARD, SOFT, WEAK. Note: I originally marked this field as final, but then this class didn't compile under JDK1.2.2. -
valueType
private int valueTypeDeprecated.The reference type for values. Must be HARD, SOFT, WEAK. Note: I originally marked this field as final, but then this class didn't compile under JDK1.2.2. -
loadFactor
private float loadFactorDeprecated.The threshold variable is calculated by multiplying table.length and loadFactor. Note: I originally marked this field as final, but then this class didn't compile under JDK1.2.2. -
purgeValues
private boolean purgeValuesDeprecated.Should the value be automatically purged when the associated key has been collected? -
queue
Deprecated.ReferenceQueue used to eliminate stale mappings. See purge. -
table
Deprecated.The hash table. Its length is always a power of two. -
size
private transient int sizeDeprecated.Number of mappings in this map. -
threshold
private transient int thresholdDeprecated.When size reaches threshold, the map is resized. See resize(). -
modCount
private transient volatile int modCountDeprecated.Number of times this map has been modified. -
keySet
Deprecated.Cached key set. May be null if key set is never accessed. -
entrySet
Deprecated.Cached entry set. May be null if entry set is never accessed. -
values
Deprecated.Cached values. May be null if values() is never accessed.
-
-
Constructor Details
-
ReferenceMap
public ReferenceMap()Deprecated.Constructs a newReferenceMap
that will use hard references to keys and soft references to values. -
ReferenceMap
public ReferenceMap(int keyType, int valueType, boolean purgeValues) Deprecated.Constructs a newReferenceMap
that will use the specified types of references. -
ReferenceMap
public ReferenceMap(int keyType, int valueType) Deprecated.Constructs a newReferenceMap
that will use the specified types of references. -
ReferenceMap
public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues) Deprecated.Constructs a newReferenceMap
with the specified reference types, load factor and initial capacity.- Parameters:
keyType
- the type of reference to use for keys; must beHARD
,SOFT
,WEAK
valueType
- the type of reference to use for values; must beHARD
,SOFT
,WEAK
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
-
ReferenceMap
public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor) Deprecated.Constructs a newReferenceMap
with the specified reference types, load factor and initial capacity.
-
-
Method Details
-
verify
Deprecated. -
writeObject
Deprecated.Writes this object to the given output stream.- Parameters:
out
- the output stream to write to- Throws:
IOException
- if the stream raises it
-
readObject
Deprecated.Reads the contents of this object from the given input stream.- Parameters:
inp
- the input stream to read from- Throws:
IOException
- if the stream raises itClassNotFoundException
- if the stream raises it
-
toReference
Deprecated.Constructs a reference of the given type to the given referent. The reference is registered with the queue for later purging.- Parameters:
type
- HARD, SOFT or WEAKreferent
- the object to refer tohash
- the hash code of the key of the mapping; this number might be different from referent.hashCode() if the referent represents a value and not a key
-
getEntry
Deprecated.Returns the entry associated with the given key.- Parameters:
key
- the key of the entry to look up- Returns:
- the entry associated with that key, or null if the key is not in this map
-
indexFor
private int indexFor(int hash) Deprecated.Converts the given hash code into an index into the hash table. -
resize
private void resize()Deprecated.Resizes this hash table by doubling its capacity. This is an expensive operation, as entries must be copied from the old smaller table to the new bigger table. -
purge
private void purge()Deprecated.Purges stale mappings from this map.Ordinarily, stale mappings are only removed during a write operation, although this method is called for both read and write operations to maintain a consistent state.
Note that this method is not synchronized! Special care must be taken if, for instance, you want stale mappings to be removed on a periodic basis by some background thread.
-
purge
Deprecated. -
size
public int size()Deprecated.Returns the size of this map.- Specified by:
size
in interfaceMap
- Overrides:
size
in classAbstractMap
- Returns:
- the size of this map
-
isEmpty
public boolean isEmpty()Deprecated.Returnstrue
if this map is empty.- Specified by:
isEmpty
in interfaceMap
- Overrides:
isEmpty
in classAbstractMap
- Returns:
true
if this map is empty
-
containsKey
Deprecated.Returnstrue
if this map contains the given key.- Specified by:
containsKey
in interfaceMap
- Overrides:
containsKey
in classAbstractMap
- Returns:
- true if the given key is in this map
-
get
Deprecated.Returns the value associated with the given key, if any.- Specified by:
get
in interfaceMap
- Overrides:
get
in classAbstractMap
- Returns:
- the value associated with the given key, or
null
if the key maps to no value
-
put
Deprecated.Associates the given key with the given value.Neither the key nor the value may be null.
- Specified by:
put
in interfaceMap
- Overrides:
put
in classAbstractMap
- Parameters:
key
- the key of the mappingvalue
- 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
-
remove
Deprecated.Removes the key and its associated value from this map.- Specified by:
remove
in interfaceMap
- Overrides:
remove
in classAbstractMap
- Parameters:
key
- the key to remove- Returns:
- the value associated with that key, or null if the key was not in the map
-
clear
public void clear()Deprecated.Clears this map.- Specified by:
clear
in interfaceMap
- Overrides:
clear
in classAbstractMap
-
entrySet
Deprecated.Returns a set view of this map's entries.- Specified by:
entrySet
in interfaceMap
- Specified by:
entrySet
in classAbstractMap
- Returns:
- a set view of this map's entries
-
keySet
Deprecated.Returns a set view of this map's keys.- Specified by:
keySet
in interfaceMap
- Overrides:
keySet
in classAbstractMap
- Returns:
- a set view of this map's keys
-
values
Deprecated.Returns a collection view of this map's values.- Specified by:
values
in interfaceMap
- Overrides:
values
in classAbstractMap
- Returns:
- a collection view of this map's values.
-