Class SoftValueHashMap<K,​V>

  • Type Parameters:
    K - The type of keys in the map.
    V - The type of values in the map.
    All Implemented Interfaces:
    Map<K,​V>

    public class SoftValueHashMap<K,​V>
    extends AbstractMap<K,​V>
    A hash map implementation that uses soft references, leaving memory when an entry is not used anymore and memory is low.

    This map implementation actually maintains some of the first entries as hard references. Only oldest entries are retained by soft references, in order to avoid too aggressive garbage collection. The amount of entries to retain by hard reference is specified at construction time.

    This map is thread-safe. It accepts the null key; it does not accept the null value. Usage of value, key or entry collections are supported. The iterator on the ConcurrentHashMap is weakly consistent.

    Since:
    2.3
    Author:
    Simone Giannecchini, Martin Desruisseaux, Ugo Moschini
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static interface  SoftValueHashMap.ValueCleaner<K,​V>
      A delegate that can be used to perform clean up operation, such as resource closing, before the values cached in soft part of the cache gets disposed of
      • Nested classes/interfaces inherited from class AbstractMap

        AbstractMap.SimpleEntry<K extends Object,​V extends Object>, AbstractMap.SimpleImmutableEntry<K extends Object,​V extends Object>
      • Nested classes/interfaces inherited from interface Map

        Map.Entry<K extends Object,​V extends Object>
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Removes all mappings from this map.
      boolean containsKey​(Object key)
      Returns true if this map contains a mapping for the specified key.
      boolean containsValue​(Object value)
      Returns true if this map maps one or more keys to this value.
      Set<Map.Entry<K,​V>> entrySet()
      Returns a set view of the mappings contained in this map.
      boolean equals​(Object object)
      Compares the specified object with this map for equality.
      V get​(Object key)
      Returns the value to which this map maps the specified key.
      int getHardReferencesCount()
      Returns the number of hard references kept in this cache
      int hashCode()
      Returns the hash code value for this map.
      V put​(K key, V value)
      Associates the specified value with the specified key in this map.
      void putAll​(Map<? extends K,​? extends V> map)
      Copies all of the mappings from the specified map to this map.
      V remove​(Object key)
      Removes the mapping for this key from this map if present.
      int size()
      Returns the number of entries in this map.
      String toString()
      Returns a string representation of this map.
      • Methods inherited from class AbstractMap

        clone, isEmpty, keySet, values
      • Methods inherited from class Object

        finalize, getClass, notify, notifyAll, wait, wait, wait
      • Methods inherited from interface Map

        compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
    • Constructor Detail

      • SoftValueHashMap

        public SoftValueHashMap()
        Creates a map with the default hard references count.
      • SoftValueHashMap

        public SoftValueHashMap​(int hardReferencesCount)
        Creates a map with the specified hard references count.
        Parameters:
        hardReferencesCount - The maximal number of hard references to keep.
      • SoftValueHashMap

        public SoftValueHashMap​(int hardReferencesCount,
                                SoftValueHashMap.ValueCleaner cleaner)
        Creates a map with the specified hard references count.
        Parameters:
        hardReferencesCount - The maximal number of hard references to keep.
    • Method Detail

      • getHardReferencesCount

        public int getHardReferencesCount()
        Returns the number of hard references kept in this cache
      • size

        public int size()
        Returns the number of entries in this map.
        Specified by:
        size in interface Map<K,​V>
        Overrides:
        size in class AbstractMap<K,​V>
      • containsKey

        public boolean containsKey​(Object key)
        Returns true if this map contains a mapping for the specified key.
        Specified by:
        containsKey in interface Map<K,​V>
        Overrides:
        containsKey in class AbstractMap<K,​V>
      • containsValue

        public boolean containsValue​(Object value)
        Returns true if this map maps one or more keys to this value.
        Specified by:
        containsValue in interface Map<K,​V>
        Overrides:
        containsValue in class AbstractMap<K,​V>
      • get

        public V get​(Object key)
        Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key, or the value has been garbage collected.
        Specified by:
        get in interface Map<K,​V>
        Overrides:
        get in class AbstractMap<K,​V>
        Parameters:
        key - key whose associated value is to be returned.
        Returns:
        the value to which this map maps the specified key, or null if none.
      • put

        public V put​(K key,
                     V value)
        Associates the specified value with the specified key in this map.
        Specified by:
        put in interface Map<K,​V>
        Overrides:
        put in class AbstractMap<K,​V>
        Parameters:
        key - Key with which the specified value is to be associated.
        value - Value to be associated with the specified key. The value can't be null.
        Returns:
        Previous value associated with specified key, or null if there was no mapping for key.
      • putAll

        public void putAll​(Map<? extends K,​? extends V> map)
        Copies all of the mappings from the specified map to this map.
        Specified by:
        putAll in interface Map<K,​V>
        Overrides:
        putAll in class AbstractMap<K,​V>
        Parameters:
        map - Mappings to be stored in this map.
      • remove

        public V remove​(Object key)
        Removes the mapping for this key from this map if present.
        Specified by:
        remove in interface Map<K,​V>
        Overrides:
        remove in class AbstractMap<K,​V>
        Parameters:
        key - Key whose mapping is to be removed from the map.
        Returns:
        previous value associated with specified key, or null if there was no entry for key.
      • clear

        public void clear()
        Removes all mappings from this map.
        Specified by:
        clear in interface Map<K,​V>
        Overrides:
        clear in class AbstractMap<K,​V>
      • entrySet

        public Set<Map.Entry<K,​V>> entrySet()
        Returns a set view of the mappings contained in this map.
        Specified by:
        entrySet in interface Map<K,​V>
        Specified by:
        entrySet in class AbstractMap<K,​V>
      • equals

        public boolean equals​(Object object)
        Compares the specified object with this map for equality.
        Specified by:
        equals in interface Map<K,​V>
        Overrides:
        equals in class AbstractMap<K,​V>
        Parameters:
        object - The object to compare with this map for equality.
      • hashCode

        public int hashCode()
        Returns the hash code value for this map.
        Specified by:
        hashCode in interface Map<K,​V>
        Overrides:
        hashCode in class AbstractMap<K,​V>
      • toString

        public String toString()
        Returns a string representation of this map.
        Overrides:
        toString in class AbstractMap<K,​V>