Package org.apache.commons.collections4.map

Class AbstractReferenceMap<K,​V>

  • Type Parameters:
    K - the type of the keys in this map
    V - the type of the values in this map
    All Implemented Interfaces:
    java.util.Map<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, Put<K,​V>
    Direct Known Subclasses:
    ReferenceIdentityMap, ReferenceMap
    public abstract class AbstractReferenceMap<K,​V>
extends AbstractHashedMap<K,​V>
    An abstract implementation of a hash-based map that allows the entries to be removed by the garbage collector.

    This class implements all the features necessary for a subclass reference hash-based map. Key-value entries are stored in instances of the ReferenceEntry class which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

    Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

    When you construct an AbstractReferenceMap, you can specify what kind of references are used to store the map's keys and values. If non-hard references are used, then the garbage collector can remove mappings if a key or value becomes unreachable, or if the JVM's memory is running low. For information on how the different reference types behave, see Reference.

    Different types of references can be specified for keys and values. The keys can be configured to be weak but the values hard, in which case this class will behave like a WeakHashMap. However, you can also specify hard keys and weak values, or any other combination. The default constructor uses hard keys and soft values, providing a memory-sensitive cache.

    This Map implementation does not allow null elements. Attempting to add a null key or value to the map will raise a NullPointerException.

    All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

    This implementation is not synchronized. You can use Collections.synchronizedMap(java.util.Map<K, V>) to provide synchronized access to a ReferenceMap.

    Since:
    3.1 (extracted from ReferenceMap in 3.0)
    See Also:
    Reference

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static class  AbstractReferenceMap.ReferenceStrength
      Reference type enum.

      • 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>

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Clears this map.
      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.
      java.util.Set<java.util.Map.Entry<K,​V>> entrySet()
      Returns a set view of this map's entries.
      V get​(java.lang.Object key)
      Gets the value mapped to the key specified.
      boolean isEmpty()
      Checks whether the map is currently empty.
      java.util.Set<K> keySet()
      Returns a set view of this map's keys.
      MapIterator<K,​V> mapIterator()
      Gets a MapIterator over the reference map.
      V put​(K key, V value)
      Puts a key-value mapping into this map.
      V remove​(java.lang.Object key)
      Removes the specified mapping from this map.
      int size()
      Gets the size of the map.
      java.util.Collection<V> values()
      Returns a collection view of this map's values.

      • Methods inherited from class java.lang.Object

        getClass, notify, notifyAll, wait, wait, wait

      • Methods inherited from interface java.util.Map

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

    • Method Detail

      • size

        public int size()
        Gets the size of the map.
        Specified by:
        size in interface Get<K,​V>
        Specified by:
        size in interface java.util.Map<K,​V>
        Overrides:
        size in class AbstractHashedMap<K,​V>
        Returns:
        the size
        See Also:
        Map.size()

      • isEmpty

        public boolean isEmpty()
        Checks whether the map is currently empty.
        Specified by:
        isEmpty in interface Get<K,​V>
        Specified by:
        isEmpty in interface java.util.Map<K,​V>
        Overrides:
        isEmpty in class AbstractHashedMap<K,​V>
        Returns:
        true if the map is currently size zero
        See Also:
        Map.isEmpty()

      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Checks whether the map contains the specified key.
        Specified by:
        containsKey in interface Get<K,​V>
        Specified by:
        containsKey in interface java.util.Map<K,​V>
        Overrides:
        containsKey in class AbstractHashedMap<K,​V>
        Parameters:
        key - the key to search for
        Returns:
        true if the map contains the key
        See Also:
        Map.containsKey(Object)

      • containsValue

        public boolean containsValue​(java.lang.Object value)
        Checks whether the map contains the specified value.
        Specified by:
        containsValue in interface Get<K,​V>
        Specified by:
        containsValue in interface java.util.Map<K,​V>
        Overrides:
        containsValue in class AbstractHashedMap<K,​V>
        Parameters:
        value - the value to search for
        Returns:
        true if the map contains the value
        See Also:
        Map.containsValue(Object)

      • get

        public V get​(java.lang.Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface Get<K,​V>
        Specified by:
        get in interface java.util.Map<K,​V>
        Overrides:
        get in class AbstractHashedMap<K,​V>
        Parameters:
        key - the key
        Returns:
        the mapped value, null if no match
        See Also:
        Map.get(Object)

      • put

        public V put​(K key,
             V value)
        Puts a key-value mapping into this map. Neither the key nor the value may be null.
        Specified by:
        put in interface java.util.Map<K,​V>
        Specified by:
        put in interface Put<K,​V>
        Overrides:
        put in class AbstractHashedMap<K,​V>
        Parameters:
        key - the key to add, must not be null
        value - the value to add, must not be null
        Returns:
        the value previously mapped to this key, null if none
        Throws:
        java.lang.NullPointerException - if either the key or value is null
        See Also:
        Map.put(Object, Object)

      • remove

        public V remove​(java.lang.Object key)
        Removes the specified mapping from this map.
        Specified by:
        remove in interface Get<K,​V>
        Specified by:
        remove in interface java.util.Map<K,​V>
        Overrides:
        remove in class AbstractHashedMap<K,​V>
        Parameters:
        key - the mapping to remove
        Returns:
        the value mapped to the removed key, null if key not in map
        See Also:
        Map.remove(Object)

      • clear

        public void clear()
        Clears this map.
        Specified by:
        clear in interface java.util.Map<K,​V>
        Specified by:
        clear in interface Put<K,​V>
        Overrides:
        clear in class AbstractHashedMap<K,​V>
        See Also:
        Map.clear()

      • entrySet

        public java.util.Set<java.util.Map.Entry<K,​V>> entrySet()
        Returns a set view of this map's entries. An iterator returned entry is valid until next() is called again. The setValue() method on the toArray entries has no effect.
        Specified by:
        entrySet in interface Get<K,​V>
        Specified by:
        entrySet in interface java.util.Map<K,​V>
        Overrides:
        entrySet in class AbstractHashedMap<K,​V>
        Returns:
        a set view of this map's entries
        See Also:
        Map.entrySet()

      • keySet

        public java.util.Set<K> keySet()
        Returns a set view of this map's keys.
        Specified by:
        keySet in interface Get<K,​V>
        Specified by:
        keySet in interface java.util.Map<K,​V>
        Overrides:
        keySet in class AbstractHashedMap<K,​V>
        Returns:
        a set view of this map's keys
        See Also:
        Map.keySet()

      • values

        public java.util.Collection<V> values()
        Returns a collection view of this map's values.
        Specified by:
        values in interface Get<K,​V>
        Specified by:
        values in interface java.util.Map<K,​V>
        Overrides:
        values in class AbstractHashedMap<K,​V>
        Returns:
        a set view of this map's values
        See Also:
        Map.values()