Package org.apache.commons.collections.map

Class AbstractReferenceMap

java.lang.Object
java.util.AbstractMap
org.apache.commons.collections.map.AbstractHashedMap
org.apache.commons.collections.map.AbstractReferenceMap
All Implemented Interfaces:
Map, IterableMap
Direct Known Subclasses:
ReferenceIdentityMap, ReferenceMap
@Deprecated(since="2021-04-30") public abstract class AbstractReferenceMap extends AbstractHashedMap
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.
An abstract implementation of a hash-based map that allows the entries to be removed by the garbage collector.

This class implements all the features necessary for a subclass reference hash-based map. Key-value entries are stored in instances of the ReferenceEntry class which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

When you construct an AbstractReferenceMap, 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 implementation does not allow null elements. Attempting to add a null key or value to the map will raise a NullPointerException.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

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 3.1 (extracted from ReferenceMap in 3.0)
See Also:

  • Field Details

    • HARD

      public static final int HARD
      Deprecated.
      Constant indicating that hard references should be used
      See Also:

    • SOFT

      public static final int SOFT
      Deprecated.
      Constant indicating that soft references should be used
      See Also:

    • WEAK

      public static final int WEAK
      Deprecated.
      Constant indicating that weak references should be used
      See Also:

  • Method Details

    • size

      public int size()
      Deprecated.
      Gets the size of the map.
      Specified by:
      size in interface Map
      Overrides:
      size in class AbstractHashedMap
      Returns:
      the size

    • isEmpty

      public boolean isEmpty()
      Deprecated.
      Checks whether the map is currently empty.
      Specified by:
      isEmpty in interface Map
      Overrides:
      isEmpty in class AbstractHashedMap
      Returns:
      true if the map is currently size zero

    • containsKey

      public boolean containsKey(Object key)
      Deprecated.
      Checks whether the map contains the specified key.
      Specified by:
      containsKey in interface Map
      Overrides:
      containsKey in class AbstractHashedMap
      Parameters:
      key - the key to search for
      Returns:
      true if the map contains the key

    • containsValue

      public boolean containsValue(Object value)
      Deprecated.
      Checks whether the map contains the specified value.
      Specified by:
      containsValue in interface Map
      Overrides:
      containsValue in class AbstractHashedMap
      Parameters:
      value - the value to search for
      Returns:
      true if the map contains the value

    • get

      public Object get(Object key)
      Deprecated.
      Gets the value mapped to the key specified.
      Specified by:
      get in interface Map
      Overrides:
      get in class AbstractHashedMap
      Parameters:
      key - the key
      Returns:
      the mapped value, null if no match

    • put

      public Object put(Object key, Object value)
      Deprecated.
      Puts a key-value mapping into this map. Neither the key nor the value may be null.
      Specified by:
      put in interface Map
      Overrides:
      put in class AbstractHashedMap
      Parameters:
      key - the key to add, must not be null
      value - the value to add, must not be null
      Returns:
      the value previously mapped to this key, null if none
      Throws:
      NullPointerException - if either the key or value is null

    • remove

      public Object remove(Object key)
      Deprecated.
      Removes the specified mapping from this map.
      Specified by:
      remove in interface Map
      Overrides:
      remove in class AbstractHashedMap
      Parameters:
      key - the mapping to remove
      Returns:
      the value mapped to the removed key, null if key not in map

    • clear

      public void clear()
      Deprecated.
      Clears this map.
      Specified by:
      clear in interface Map
      Overrides:
      clear in class AbstractHashedMap

    • mapIterator

      public MapIterator mapIterator()
      Deprecated.
      Gets a MapIterator over the reference map. The iterator only returns valid key/value pairs.
      Specified by:
      mapIterator in interface IterableMap
      Overrides:
      mapIterator in class AbstractHashedMap
      Returns:
      a map iterator

    • entrySet

      public Set entrySet()
      Deprecated.
      Returns a set view of this map's entries. An iterator returned entry is valid until next() is called again. The setValue() method on the toArray entries has no effect.
      Specified by:
      entrySet in interface Map
      Overrides:
      entrySet in class AbstractHashedMap
      Returns:
      a set view of this map's entries

    • keySet

      public Set keySet()
      Deprecated.
      Returns a set view of this map's keys.
      Specified by:
      keySet in interface Map
      Overrides:
      keySet in class AbstractHashedMap
      Returns:
      a set view of this map's keys

    • values

      public Collection values()
      Deprecated.
      Returns a collection view of this map's values.
      Specified by:
      values in interface Map
      Overrides:
      values in class AbstractHashedMap
      Returns:
      a set view of this map's values