Package org.apache.commons.collections

Class ReferenceMap

java.lang.Object
java.util.AbstractMap
org.apache.commons.collections.ReferenceMap
All Implemented Interfaces:
Map
public class ReferenceMap extends AbstractMap
Deprecated.
Moved to map subpackage. Due to be removed in v4.0.
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 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) $
Author:
Paul Jack
See Also:

  • Nested Class Summary

    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

    Fields
    Modifier and Type
    Field
    Description
    static final int
    HARD
    Deprecated.
    Constant indicating that hard references should be used.
    static final int
    SOFT
    Deprecated.
    Constant indicating that soft references should be used.
    static final int
    WEAK
    Deprecated.
    Constant indicating that weak references should be used.

  • 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

    Modifier and Type
    Method
    Description
    void
    clear()
    Deprecated.
    Clears this map.
    boolean
    containsKey(Object key)
    Deprecated.
    Returns true if this map contains the given key.
    Set
    entrySet()
    Deprecated.
    Returns a set view of this map's entries.
    Object
    get(Object key)
    Deprecated.
    Returns the value associated with the given key, if any.
    boolean
    isEmpty()
    Deprecated.
    Returns true if this map is empty.
    Set
    keySet()
    Deprecated.
    Returns a set view of this map's keys.
    Object
    put(Object key, Object value)
    Deprecated.
    Associates the given key with the given value.
    Object
    remove(Object key)
    Deprecated.
    Removes the key and its associated value from this map.
    int
    size()
    Deprecated.
    Returns the size of this map.
    Collection
    values()
    Deprecated.
    Returns a collection view of this map's values.

    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

    • 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:

  • 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, 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 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

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

    • 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 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

    • 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 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

  • Method Details

    • size

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

    • isEmpty

      public boolean isEmpty()
      Deprecated.
      Returns true if this map is empty.
      Specified by:
      isEmpty in interface Map
      Overrides:
      isEmpty in class AbstractMap
      Returns:
      true if this map is empty

    • containsKey

      public boolean containsKey(Object key)
      Deprecated.
      Returns true if this map contains the given key.
      Specified by:
      containsKey in interface Map
      Overrides:
      containsKey in class AbstractMap
      Returns:
      true if the given key is in this map

    • get

      public Object get(Object key)
      Deprecated.
      Returns the value associated with the given key, if any.
      Specified by:
      get in interface Map
      Overrides:
      get in class AbstractMap
      Returns:
      the value associated with the given key, or null if the key maps to no value

    • put

      public Object put(Object key, Object value)
      Deprecated.
      Associates the given key with the given value.

      Neither the key nor the value may be null.

      Specified by:
      put in interface Map
      Overrides:
      put in class AbstractMap
      Parameters:
      key - the key of the mapping
      value - 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

      public Object remove(Object key)
      Deprecated.
      Removes the key and its associated value from this map.
      Specified by:
      remove in interface Map
      Overrides:
      remove in class AbstractMap
      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 interface Map
      Overrides:
      clear in class AbstractMap

    • entrySet

      public Set entrySet()
      Deprecated.
      Returns a set view of this map's entries.
      Specified by:
      entrySet in interface Map
      Specified by:
      entrySet in class AbstractMap
      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 AbstractMap
      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 AbstractMap
      Returns:
      a collection view of this map's values.