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) $
See Also:

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    private class 
    ReferenceMap.Entry
    Deprecated.
     
    private class 
    ReferenceMap.EntryIterator
    Deprecated.
     
    private class 
    ReferenceMap.KeyIterator
    Deprecated.
     
    private static class 
    ReferenceMap.SoftRef
    Deprecated.
     
    private class 
    ReferenceMap.ValueIterator
    Deprecated.
     
    private static class 
    ReferenceMap.WeakRef
    Deprecated.
     

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

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

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private Set
    entrySet
    Deprecated.
    Cached entry set.
    static final int
    HARD
    Deprecated.
    Constant indicating that hard references should be used.
    private Set
    keySet
    Deprecated.
    Cached key set.
    private int
    keyType
    Deprecated.
    The reference type for keys.
    private float
    loadFactor
    Deprecated.
    The threshold variable is calculated by multiplying table.length and loadFactor.
    private int
    modCount
    Deprecated.
    Number of times this map has been modified.
    private boolean
    purgeValues
    Deprecated.
    Should the value be automatically purged when the associated key has been collected?
    private ReferenceQueue
    queue
    Deprecated.
    ReferenceQueue used to eliminate stale mappings.
    private static final long
    serialVersionUID
    Deprecated.
    For serialization.
    private int
    size
    Deprecated.
    Number of mappings in this map.
    static final int
    SOFT
    Deprecated.
    Constant indicating that soft references should be used.
    private ReferenceMap.Entry[]
    table
    Deprecated.
    The hash table.
    private int
    threshold
    Deprecated.
    When size reaches threshold, the map is resized.
    private Collection
    values
    Deprecated.
    Cached values.
    private int
    valueType
    Deprecated.
    The reference type for values.
    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.
    private ReferenceMap.Entry
    getEntry(Object key)
    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.
    Returns true if this map is empty.
    Set
    keySet()
    Deprecated.
    Returns a set view of this map's keys.
    private void
    purge()
    Deprecated.
    Purges stale mappings from this map.
    private void
    purge(Reference ref)
    Deprecated.
     
    Object
    put(Object key, Object value)
    Deprecated.
    Associates the given key with the given value.
    private void
    readObject(ObjectInputStream inp)
    Deprecated.
    Reads the contents of this object from the given input stream.
    Object
    remove(Object key)
    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.
    Collection
    values()
    Deprecated.
    Returns a collection view of this map's values.
    private static void
    verify(String name, int type)
    Deprecated.
     
    private void
    writeObject(ObjectOutputStream out)
    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 serialVersionUID
      Deprecated.
      For serialization.
      See Also:

    • 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:

    • keyType

      private int keyType
      Deprecated.
      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 valueType
      Deprecated.
      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 loadFactor
      Deprecated.
      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 purgeValues
      Deprecated.
      Should the value be automatically purged when the associated key has been collected?

    • queue

      private transient ReferenceQueue queue
      Deprecated.
      ReferenceQueue used to eliminate stale mappings. See purge.

    • table

      private transient ReferenceMap.Entry[] table
      Deprecated.
      The hash table. Its length is always a power of two.

    • size

      private transient int size
      Deprecated.
      Number of mappings in this map.

    • threshold

      private transient int threshold
      Deprecated.
      When size reaches threshold, the map is resized. See resize().

    • modCount

      private transient volatile int modCount
      Deprecated.
      Number of times this map has been modified.

    • keySet

      private transient Set keySet
      Deprecated.
      Cached key set. May be null if key set is never accessed.

    • entrySet

      private transient Set entrySet
      Deprecated.
      Cached entry set. May be null if entry set is never accessed.

    • values

      private transient Collection values
      Deprecated.
      Cached values. May be null if values() is never accessed.

  • 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

    • verify

      private static void verify(String name, int type)
      Deprecated.

    • writeObject

      private void writeObject(ObjectOutputStream out) throws IOException
      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

      private void readObject(ObjectInputStream inp) throws IOException, ClassNotFoundException
      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 it
      ClassNotFoundException - if the stream raises it

    • toReference

      private Object toReference(int type, Object referent, int hash)
      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 WEAK
      referent - the object to refer to
      hash - 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

      private ReferenceMap.Entry getEntry(Object key)
      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

      private void purge(Reference ref)
      Deprecated.

    • 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.