Package org.apache.commons.collections.map

Class ReferenceMap

java.lang.Object

java.util.AbstractMap

org.apache.commons.collections.map.AbstractHashedMap

org.apache.commons.collections.map.AbstractReferenceMap

org.apache.commons.collections.map.ReferenceMap

All Implemented Interfaces:

Serializable, Map, IterableMap

@Deprecated(since="2021-04-30")
public class ReferenceMap
extends AbstractReferenceMap
implements Serializable

Deprecated.

Apache Commons Collections version 3.x is being deprecated from AEMaaCS. The upgraded version 4.4 of Commons Collections is already included as replacement. Customers are advised to upgrade to this version of the library. Please note: the package name was changed to org.apache.commons.collections4. Further note that there are AEM APIs currently exposing the old collections classes; these will be updated in upcoming releases.

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 Collections.synchronizedMap(java.util.Map<K, V>) 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 that ReferenceMap 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 Collections.synchronizedMap(java.util.Map<K, V>). This class may throw exceptions when accessed by concurrent threads without synchronization.

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.

Since:

Commons Collections 3.0 (previously in main package v2.1)

See Also:

• Reference
• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Field Summary

Fields inherited from class org.apache.commons.collections.map.AbstractReferenceMap

HARD, SOFT, WEAK

Constructor Summary

Constructors

Constructor	Description
ReferenceMap()	Deprecated. Constructs a new ReferenceMap that will use hard references to keys and soft references to values.
ReferenceMap(int keyType, int valueType)	Deprecated. Constructs a new ReferenceMap that will use the specified types of references.
ReferenceMap(int keyType, int valueType, boolean purgeValues)	Deprecated. Constructs a new ReferenceMap that will use the specified types of references.
ReferenceMap(int keyType, int valueType, int capacity, float loadFactor)	Deprecated. Constructs a new ReferenceMap with the specified reference types, load factor and initial capacity.
ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues)	Deprecated. Constructs a new ReferenceMap with the specified reference types, load factor and initial capacity.

Method Summary

Methods inherited from class org.apache.commons.collections.map.AbstractReferenceMap

clear, containsKey, containsValue, entrySet, get, isEmpty, keySet, mapIterator, put, remove, size, values

Methods inherited from class org.apache.commons.collections.map.AbstractHashedMap

equals, hashCode, putAll, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

Constructor Details

ReferenceMap

public ReferenceMap()

Deprecated.

Constructs a new ReferenceMap that will use hard references to keys and soft references to values.

ReferenceMap

public ReferenceMap(int keyType,
 int valueType)

Deprecated.

Constructs a new ReferenceMap that will use the specified types of references.

Parameters:

keyType - the type of reference to use for keys; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

valueType - the type of reference to use for values; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

ReferenceMap

public ReferenceMap(int keyType,
 int valueType,
 boolean purgeValues)

Deprecated.

Constructs a new ReferenceMap that will use the specified types of references.

Parameters:

keyType - the type of reference to use for keys; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

valueType - the type of reference to use for values; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

purgeValues - 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 new ReferenceMap with the specified reference types, load factor and initial capacity.

Parameters:

keyType - the type of reference to use for keys; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

valueType - the type of reference to use for values; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

capacity - the initial capacity for the map

loadFactor - the load factor for the map

ReferenceMap

public ReferenceMap(int keyType,
 int valueType,
 int capacity,
 float loadFactor,
 boolean purgeValues)

Deprecated.

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 AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

valueType - the type of reference to use for values; must be AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT, AbstractReferenceMap.WEAK

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