Package org.apache.commons.collections4.map

Class ReferenceIdentityMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.commons.collections4.map.AbstractHashedMap<K,V>
org.apache.commons.collections4.map.AbstractReferenceMap<K,V>
org.apache.commons.collections4.map.ReferenceIdentityMap<K,V>
Type Parameters:
K - the type of the keys in this map
V - the type of the values in this map
All Implemented Interfaces:
Serializable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>
public class ReferenceIdentityMap<K,V> extends AbstractReferenceMap<K,V> implements Serializable
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 Collections.synchronizedMap(java.util.Map<K, V>) to provide synchronized access to a ReferenceIdentityMap. Remember that synchronization will not stop the garbage collector 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 Collections.synchronizedMap(java.util.Map<K, V>). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
3.0 (previously in main package v2.1)
See Also:

  • Constructor Details

    • ReferenceIdentityMap

      public ReferenceIdentityMap()
      Constructs a new ReferenceIdentityMap that will use hard references to keys and soft references to values.

    • ReferenceIdentityMap

      public ReferenceIdentityMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType)
      Constructs a new ReferenceIdentityMap that will use the specified types of references.
      Parameters:
      keyType - the type of reference to use for keys; must be HARD, SOFT, WEAK
      valueType - the type of reference to use for values; must be HARD, SOFT, WEAK

    • ReferenceIdentityMap

      public ReferenceIdentityMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, boolean purgeValues)
      Constructs a new ReferenceIdentityMap that will use the specified types of references.
      Parameters:
      keyType - the type of reference to use for keys; must be HARD, SOFT, WEAK
      valueType - the type of reference to use for values; must be HARD, SOFT, WEAK
      purgeValues - should the value be automatically purged when the key is garbage collected

    • ReferenceIdentityMap

      public ReferenceIdentityMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int capacity, float loadFactor)
      Constructs a new ReferenceIdentityMap with the specified reference types, load factor and initial capacity.
      Parameters:
      keyType - the type of reference to use for keys; must be HARD, SOFT, WEAK
      valueType - the type of reference to use for values; must be HARD, SOFT, WEAK
      capacity - the initial capacity for the map
      loadFactor - the load factor for the map

    • ReferenceIdentityMap

      public ReferenceIdentityMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int capacity, float loadFactor, boolean purgeValues)
      Constructs a new ReferenceIdentityMap with the specified reference types, load factor and initial capacity.
      Parameters:
      keyType - the type of reference to use for keys; must be HARD, SOFT, WEAK
      valueType - the type of reference to use for values; must be HARD, SOFT, 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