Package org.apache.commons.collections.map

Class 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:
    Serialized Form

    • Constructor Detail

      • 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 Detail

      • 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

      • clone

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