Package org.apache.commons.collections.map

Class IdentityMap

java.lang.Object
java.util.AbstractMap
org.apache.commons.collections.map.AbstractHashedMap
org.apache.commons.collections.map.IdentityMap
All Implemented Interfaces:
Serializable, Cloneable, Map, IterableMap
public class IdentityMap extends AbstractHashedMap implements Serializable, Cloneable
A Map implementation that matches keys and values based on == not equals().

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.

Note that IdentityMap 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(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
Commons Collections 3.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
java util HashMap, Stephen Colebourne
See Also:

  • Constructor Details

    • IdentityMap

      public IdentityMap()
      Constructs a new empty map with default size and load factor.

    • IdentityMap

      public IdentityMap(int initialCapacity)
      Constructs a new, empty map with the specified initial capacity.
      Parameters:
      initialCapacity - the initial capacity
      Throws:
      IllegalArgumentException - if the initial capacity is less than one

    • IdentityMap

      public IdentityMap(int initialCapacity, float loadFactor)
      Constructs a new, empty map with the specified initial capacity and load factor.
      Parameters:
      initialCapacity - the initial capacity
      loadFactor - the load factor
      Throws:
      IllegalArgumentException - if the initial capacity is less than one
      IllegalArgumentException - if the load factor is less than zero

    • IdentityMap

      public IdentityMap(Map map)
      Constructor copying elements from another map.
      Parameters:
      map - the map to copy
      Throws:
      NullPointerException - if the map is null

  • Method Details

    • hash

      protected int hash(Object key)
      Gets the hash code for the key specified. This implementation uses the identity hash code.
      Overrides:
      hash in class AbstractHashedMap
      Parameters:
      key - the key to get a hash code for
      Returns:
      the hash code

    • isEqualKey

      protected boolean isEqualKey(Object key1, Object key2)
      Compares two keys for equals. This implementation uses ==.
      Overrides:
      isEqualKey in class AbstractHashedMap
      Parameters:
      key1 - the first key to compare
      key2 - the second key to compare
      Returns:
      true if equal by identity

    • isEqualValue

      protected boolean isEqualValue(Object value1, Object value2)
      Compares two values for equals. This implementation uses ==.
      Overrides:
      isEqualValue in class AbstractHashedMap
      Parameters:
      value1 - the first value to compare
      value2 - the second value to compare
      Returns:
      true if equal by identity

    • createEntry

      protected AbstractHashedMap.HashEntry createEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)
      Creates an entry to store the data. This implementation creates an IdentityEntry instance.
      Overrides:
      createEntry in class AbstractHashedMap
      Parameters:
      next - the next entry in sequence
      hashCode - the hash code to use
      key - the key to store
      value - the value to store
      Returns:
      the newly created entry

    • clone

      public Object clone()
      Clones the map without cloning the keys or values.
      Overrides:
      clone in class AbstractHashedMap
      Returns:
      a shallow clone