Package org.apache.commons.collections

Class FastHashMap

  • All Implemented Interfaces:
    java.io.Serializable, java.lang.Cloneable, java.util.Map
    public class FastHashMap
extends java.util.HashMap

    A customized implementation of java.util.HashMap designed to operate in a multithreaded environment where the large majority of method calls are read-only, instead of structural changes. When operating in "fast" mode, read calls are non-synchronized and write calls perform the following steps:

    • Clone the existing collection
    • Perform the modification on the clone
    • Replace the existing collection with the (modified) clone

    When first created, objects of this class default to "slow" mode, where all accesses of any type are synchronized but no cloning takes place. This is appropriate for initially populating the collection, followed by a switch to "fast" mode (by calling setFast(true)) after initialization is complete.

    NOTE: If you are creating and accessing a HashMap only within a single thread, you should use java.util.HashMap directly (with no synchronization), for maximum performance.

    NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declaration.

    Since:
    Commons Collections 1.0
    See Also:
    Serialized Form

    • Nested Class Summary

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

        java.util.AbstractMap.SimpleEntry<K extends java.lang.Object,​V extends java.lang.Object>, java.util.AbstractMap.SimpleImmutableEntry<K extends java.lang.Object,​V extends java.lang.Object>

      • Nested classes/interfaces inherited from interface java.util.Map

        java.util.Map.Entry<K extends java.lang.Object,​V extends java.lang.Object>

    • Constructor Summary

      Constructors 
      Constructor Description
      FastHashMap()
      Construct an empty map.
      FastHashMap​(int capacity)
      Construct an empty map with the specified capacity.
      FastHashMap​(int capacity, float factor)
      Construct an empty map with the specified capacity and load factor.
      FastHashMap​(java.util.Map map)
      Construct a new map with the same mappings as the specified map.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Remove all mappings from this map.
      java.lang.Object clone()
      Return a shallow copy of this FastHashMap instance.
      boolean containsKey​(java.lang.Object key)
      Return true if this map contains a mapping for the specified key.
      boolean containsValue​(java.lang.Object value)
      Return true if this map contains one or more keys mapping to the specified value.
      java.util.Set entrySet()
      Return a collection view of the mappings contained in this map.
      boolean equals​(java.lang.Object o)
      Compare the specified object with this list for equality.
      java.lang.Object get​(java.lang.Object key)
      Return the value to which this map maps the specified key.
      boolean getFast()
      Returns true if this map is operating in fast mode.
      int hashCode()
      Return the hash code value for this map.
      boolean isEmpty()
      Return true if this map contains no mappings.
      java.util.Set keySet()
      Return a set view of the keys contained in this map.
      java.lang.Object put​(java.lang.Object key, java.lang.Object value)
      Associate the specified value with the specified key in this map.
      void putAll​(java.util.Map in)
      Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.
      java.lang.Object remove​(java.lang.Object key)
      Remove any mapping for this key, and return any previously mapped value.
      void setFast​(boolean fast)
      Sets whether this map is operating in fast mode.
      int size()
      Return the number of key-value mappings in this map.
      java.util.Collection values()
      Return a collection view of the values contained in this map.

      • Methods inherited from class java.util.HashMap

        compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

      • Methods inherited from class java.util.AbstractMap

        toString

      • Methods inherited from class java.lang.Object

        getClass, notify, notifyAll, wait, wait, wait

    • Constructor Detail

      • FastHashMap

        public FastHashMap()
        Construct an empty map.

      • FastHashMap

        public FastHashMap​(int capacity)
        Construct an empty map with the specified capacity.
        Parameters:
        capacity - the initial capacity of the empty map

      • FastHashMap

        public FastHashMap​(int capacity,
                   float factor)
        Construct an empty map with the specified capacity and load factor.
        Parameters:
        capacity - the initial capacity of the empty map
        factor - the load factor of the new map

      • FastHashMap

        public FastHashMap​(java.util.Map map)
        Construct a new map with the same mappings as the specified map.
        Parameters:
        map - the map whose mappings are to be copied

    • Method Detail

      • getFast

        public boolean getFast()
        Returns true if this map is operating in fast mode.
        Returns:
        true if this map is operating in fast mode

      • setFast

        public void setFast​(boolean fast)
        Sets whether this map is operating in fast mode.
        Parameters:
        fast - true if this map should operate in fast mode

      • get

        public java.lang.Object get​(java.lang.Object key)
        Return the value to which this map maps the specified key. Returns null if the map contains no mapping for this key, or if there is a mapping with a value of null. Use the containsKey() method to disambiguate these cases.
        Specified by:
        get in interface java.util.Map
        Overrides:
        get in class java.util.HashMap
        Parameters:
        key - the key whose value is to be returned
        Returns:
        the value mapped to that key, or null

      • size

        public int size()
        Return the number of key-value mappings in this map.
        Specified by:
        size in interface java.util.Map
        Overrides:
        size in class java.util.HashMap
        Returns:
        the current size of the map

      • isEmpty

        public boolean isEmpty()
        Return true if this map contains no mappings.
        Specified by:
        isEmpty in interface java.util.Map
        Overrides:
        isEmpty in class java.util.HashMap
        Returns:
        is the map currently empty

      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Return true if this map contains a mapping for the specified key.
        Specified by:
        containsKey in interface java.util.Map
        Overrides:
        containsKey in class java.util.HashMap
        Parameters:
        key - the key to be searched for
        Returns:
        true if the map contains the key

      • containsValue

        public boolean containsValue​(java.lang.Object value)
        Return true if this map contains one or more keys mapping to the specified value.
        Specified by:
        containsValue in interface java.util.Map
        Overrides:
        containsValue in class java.util.HashMap
        Parameters:
        value - the value to be searched for
        Returns:
        true if the map contains the value

      • put

        public java.lang.Object put​(java.lang.Object key,
                            java.lang.Object value)
        Associate the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced and returned.
        Specified by:
        put in interface java.util.Map
        Overrides:
        put in class java.util.HashMap
        Parameters:
        key - the key with which the value is to be associated
        value - the value to be associated with this key
        Returns:
        the value previously mapped to the key, or null

      • putAll

        public void putAll​(java.util.Map in)
        Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.
        Specified by:
        putAll in interface java.util.Map
        Overrides:
        putAll in class java.util.HashMap
        Parameters:
        in - the map whose mappings are to be copied

      • remove

        public java.lang.Object remove​(java.lang.Object key)
        Remove any mapping for this key, and return any previously mapped value.
        Specified by:
        remove in interface java.util.Map
        Overrides:
        remove in class java.util.HashMap
        Parameters:
        key - the key whose mapping is to be removed
        Returns:
        the value removed, or null

      • clear

        public void clear()
        Remove all mappings from this map.
        Specified by:
        clear in interface java.util.Map
        Overrides:
        clear in class java.util.HashMap

      • equals

        public boolean equals​(java.lang.Object o)
        Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for the Map.equals method.
        Specified by:
        equals in interface java.util.Map
        Overrides:
        equals in class java.util.AbstractMap
        Parameters:
        o - the object to be compared to this list
        Returns:
        true if the two maps are equal

      • hashCode

        public int hashCode()
        Return the hash code value for this map. This implementation uses exactly the code that is used to define the list hash function in the documentation for the Map.hashCode method.
        Specified by:
        hashCode in interface java.util.Map
        Overrides:
        hashCode in class java.util.AbstractMap
        Returns:
        suitable integer hash code

      • clone

        public java.lang.Object clone()
        Return a shallow copy of this FastHashMap instance. The keys and values themselves are not copied.
        Overrides:
        clone in class java.util.HashMap
        Returns:
        a clone of this map

      • entrySet

        public java.util.Set entrySet()
        Return a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry.
        Specified by:
        entrySet in interface java.util.Map
        Overrides:
        entrySet in class java.util.HashMap

      • keySet

        public java.util.Set keySet()
        Return a set view of the keys contained in this map.
        Specified by:
        keySet in interface java.util.Map
        Overrides:
        keySet in class java.util.HashMap

      • values

        public java.util.Collection values()
        Return a collection view of the values contained in this map.
        Specified by:
        values in interface java.util.Map
        Overrides:
        values in class java.util.HashMap