Package org.apache.commons.collections.map

Class Flat3Map

  • All Implemented Interfaces:
    java.io.Serializable, java.lang.Cloneable, java.util.Map, IterableMap
    public class Flat3Map
extends java.lang.Object
implements IterableMap, java.io.Serializable, java.lang.Cloneable
    A Map implementation that stores data in simple fields until the size is greater than 3.

    This map is designed for performance and can outstrip HashMap. It also has good garbage collection characteristics.

    • Optimised for operation at size 3 or less.
    • Still works well once size 3 exceeded.
    • Gets at size 3 or less are about 0-10% faster than HashMap,
    • Puts at size 3 or less are over 4 times faster than HashMap.
    • Performance 5% slower than HashMap once size 3 exceeded once.
    The design uses two distinct modes of operation - flat and delegate. While the map is size 3 or less, operations map straight onto fields using switch statements. Once size 4 is reached, the map switches to delegate mode and only switches back when cleared. In delegate mode, all operations are forwarded straight to a HashMap resulting in the 5% performance loss.

    The performance gains on puts are due to not needing to create a Map Entry object. This is a large saving not only in performance but in garbage collection.

    Whilst in flat mode this map is also easy for the garbage collector to dispatch. This is because it contains no complex objects or arrays which slow the progress.

    Do not use Flat3Map if the size is likely to grow beyond 3.

    Note that Flat3Map 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: 1713293 $ $Date: 2015-11-08 22:04:34 +0100 (Sun, 08 Nov 2015) $
    See Also:
    Serialized Form

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private AbstractHashedMap delegateMap
      Map, used while in delegate mode
      private int hash1
      Hash, used while in flat mode
      private int hash2
      Hash, used while in flat mode
      private int hash3
      Hash, used while in flat mode
      private java.lang.Object key1
      Key, used while in flat mode
      private java.lang.Object key2
      Key, used while in flat mode
      private java.lang.Object key3
      Key, used while in flat mode
      private static long serialVersionUID
      Serialization version
      private int size
      The size of the map, used while in flat mode
      private java.lang.Object value1
      Value, used while in flat mode
      private java.lang.Object value2
      Value, used while in flat mode
      private java.lang.Object value3
      Value, used while in flat mode

    • Constructor Summary

      Constructors 
      Constructor Description
      Flat3Map()
      Constructor.
      Flat3Map​(java.util.Map map)
      Constructor copying elements from another map.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
      java.lang.Object clone()
      Clones the map without cloning the keys or values.
      boolean containsKey​(java.lang.Object key)
      Checks whether the map contains the specified key.
      boolean containsValue​(java.lang.Object value)
      Checks whether the map contains the specified value.
      private void convertToMap()
      Converts the flat map data to a map.
      protected AbstractHashedMap createDelegateMap()
      Create an instance of the map used for storage when in delegation mode.
      java.util.Set entrySet()
      Gets the entrySet view of the map.
      boolean equals​(java.lang.Object obj)
      Compares this map with another.
      java.lang.Object get​(java.lang.Object key)
      Gets the value mapped to the key specified.
      int hashCode()
      Gets the standard Map hashCode.
      boolean isEmpty()
      Checks whether the map is currently empty.
      java.util.Set keySet()
      Gets the keySet view of the map.
      MapIterator mapIterator()
      Gets an iterator over the map.
      java.lang.Object put​(java.lang.Object key, java.lang.Object value)
      Puts a key-value mapping into this map.
      void putAll​(java.util.Map map)
      Puts all the values from the specified map into this map.
      private void readObject​(java.io.ObjectInputStream in)
      Read the map in using a custom routine.
      java.lang.Object remove​(java.lang.Object key)
      Removes the specified mapping from this map.
      int size()
      Gets the size of the map.
      java.lang.String toString()
      Gets the map as a String.
      java.util.Collection values()
      Gets the values view of the map.
      private void writeObject​(java.io.ObjectOutputStream out)
      Write the map out using a custom routine.

      • 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 Detail

      • serialVersionUID

        private static final long serialVersionUID
        Serialization version
        See Also:
        Constant Field Values

      • size

        private transient int size
        The size of the map, used while in flat mode

      • hash1

        private transient int hash1
        Hash, used while in flat mode

      • hash2

        private transient int hash2
        Hash, used while in flat mode

      • hash3

        private transient int hash3
        Hash, used while in flat mode

      • key1

        private transient java.lang.Object key1
        Key, used while in flat mode

      • key2

        private transient java.lang.Object key2
        Key, used while in flat mode

      • key3

        private transient java.lang.Object key3
        Key, used while in flat mode

      • value1

        private transient java.lang.Object value1
        Value, used while in flat mode

      • value2

        private transient java.lang.Object value2
        Value, used while in flat mode

      • value3

        private transient java.lang.Object value3
        Value, used while in flat mode

      • delegateMap

        private transient AbstractHashedMap delegateMap
        Map, used while in delegate mode

    • Constructor Detail

      • Flat3Map

        public Flat3Map()
        Constructor.

      • Flat3Map

        public Flat3Map​(java.util.Map map)
        Constructor copying elements from another map.
        Parameters:
        map - the map to copy
        Throws:
        java.lang.NullPointerException - if the map is null

    • Method Detail

      • get

        public java.lang.Object get​(java.lang.Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface java.util.Map
        Parameters:
        key - the key
        Returns:
        the mapped value, null if no match

      • size

        public int size()
        Gets the size of the map.
        Specified by:
        size in interface java.util.Map
        Returns:
        the size

      • isEmpty

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

      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Checks whether the map contains the specified key.
        Specified by:
        containsKey in interface java.util.Map
        Parameters:
        key - the key to search for
        Returns:
        true if the map contains the key

      • containsValue

        public boolean containsValue​(java.lang.Object value)
        Checks whether the map contains the specified value.
        Specified by:
        containsValue in interface java.util.Map
        Parameters:
        value - the value to search for
        Returns:
        true if the map contains the key

      • put

        public java.lang.Object put​(java.lang.Object key,
                            java.lang.Object value)
        Puts a key-value mapping into this map.
        Specified by:
        put in interface java.util.Map
        Parameters:
        key - the key to add
        value - the value to add
        Returns:
        the value previously mapped to this key, null if none

      • putAll

        public void putAll​(java.util.Map map)
        Puts all the values from the specified map into this map.
        Specified by:
        putAll in interface java.util.Map
        Parameters:
        map - the map to add
        Throws:
        java.lang.NullPointerException - if the map is null

      • convertToMap

        private void convertToMap()
        Converts the flat map data to a map.

      • createDelegateMap

        protected AbstractHashedMap createDelegateMap()
        Create an instance of the map used for storage when in delegation mode.

        This can be overridden by subclasses to provide a different map implementation. Not every AbstractHashedMap is suitable, identity and reference based maps would be poor choices.

        Returns:
        a new AbstractHashedMap or subclass
        Since:
        Commons Collections 3.1

      • remove

        public java.lang.Object remove​(java.lang.Object key)
        Removes the specified mapping from this map.
        Specified by:
        remove in interface java.util.Map
        Parameters:
        key - the mapping to remove
        Returns:
        the value mapped to the removed key, null if key not in map

      • clear

        public void clear()
        Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
        Specified by:
        clear in interface java.util.Map

      • mapIterator

        public MapIterator mapIterator()
        Gets an iterator over the map. Changes made to the iterator affect this map.

        A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map Entry object.

        Specified by:
        mapIterator in interface IterableMap
        Returns:
        the map iterator

      • entrySet

        public java.util.Set entrySet()
        Gets the entrySet view of the map. Changes made to the view affect this map. The Map Entry is not an independent object and changes as the iterator progresses. To simply iterate through the entries, use mapIterator().
        Specified by:
        entrySet in interface java.util.Map
        Returns:
        the entrySet view

      • keySet

        public java.util.Set keySet()
        Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator().
        Specified by:
        keySet in interface java.util.Map
        Returns:
        the keySet view

      • values

        public java.util.Collection values()
        Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, use mapIterator().
        Specified by:
        values in interface java.util.Map
        Returns:
        the values view

      • writeObject

        private void writeObject​(java.io.ObjectOutputStream out)
                  throws java.io.IOException
        Write the map out using a custom routine.
        Throws:
        java.io.IOException

      • readObject

        private void readObject​(java.io.ObjectInputStream in)
                 throws java.io.IOException,
                        java.lang.ClassNotFoundException
        Read the map in using a custom routine.
        Throws:
        java.io.IOException
        java.lang.ClassNotFoundException

      • clone

        public java.lang.Object clone()
        Clones the map without cloning the keys or values.
        Overrides:
        clone in class java.lang.Object
        Returns:
        a shallow clone
        Since:
        Commons Collections 3.1

      • equals

        public boolean equals​(java.lang.Object obj)
        Compares this map with another.
        Specified by:
        equals in interface java.util.Map
        Overrides:
        equals in class java.lang.Object
        Parameters:
        obj - the object to compare to
        Returns:
        true if equal

      • hashCode

        public int hashCode()
        Gets the standard Map hashCode.
        Specified by:
        hashCode in interface java.util.Map
        Overrides:
        hashCode in class java.lang.Object
        Returns:
        the hash code defined in the Map interface

      • toString

        public java.lang.String toString()
        Gets the map as a String.
        Overrides:
        toString in class java.lang.Object
        Returns:
        a string version of the map