Class ConcurrentWeakKeyHashMap<K,​V>

  • Type Parameters:
    K - the type of keys maintained by this map
    V - the type of mapped values
    All Implemented Interfaces:
    java.util.concurrent.ConcurrentMap<K,​V>, java.util.Map<K,​V>

    public final class ConcurrentWeakKeyHashMap<K,​V>
    extends java.util.AbstractMap<K,​V>
    implements java.util.concurrent.ConcurrentMap<K,​V>
    An alternative weak-key ConcurrentMap which is similar to ConcurrentHashMap.
    Version:
    $Rev: 2371 $, $Date: 2010-10-19 15:00:42 +0900 (Tue, 19 Oct 2010) $
    Author:
    The Netty Project, Doug Lea, Jason T. Greene, Trustin Lee
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static interface  ConcurrentWeakKeyHashMap.ReusableIterator<E>  
      • Nested classes/interfaces inherited from class java.util.AbstractMap

        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
      ConcurrentWeakKeyHashMap()
      Creates a new, empty map with a default initial capacity (16), reference types (weak keys, strong values), default load factor (0.75) and concurrencyLevel (16).
      ConcurrentWeakKeyHashMap​(int initialCapacity)
      Creates a new, empty map with the specified initial capacity, and with default reference types (weak keys, strong values), load factor (0.75) and concurrencyLevel (16).
      ConcurrentWeakKeyHashMap​(int initialCapacity, float loadFactor)
      Creates a new, empty map with the specified initial capacity and load factor and with the default reference types (weak keys, strong values), and concurrencyLevel (16).
      ConcurrentWeakKeyHashMap​(int initialCapacity, float loadFactor, int concurrencyLevel)
      Creates a new, empty map with the specified initial capacity, load factor and concurrency level.
      ConcurrentWeakKeyHashMap​(java.util.Map<? extends K,​? extends V> m)
      Creates a new map with the same mappings as the given map.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Removes all of the mappings from this map.
      boolean contains​(java.lang.Object value)
      Legacy method testing if some key maps into the specified value in this table.
      boolean containsKey​(java.lang.Object key)
      Tests if the specified object is a key in this table.
      boolean containsValue​(java.lang.Object value)
      Returns true if this map maps one or more keys to the specified value.
      java.util.Enumeration<V> elements()
      Returns an enumeration of the values in this table.
      java.util.Set<java.util.Map.Entry<K,​V>> entrySet()
      Returns a Set view of the mappings contained in this map.
      V get​(java.lang.Object key)
      Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
      boolean isEmpty()
      Returns true if this map contains no key-value mappings.
      java.util.Enumeration<K> keys()
      Returns an enumeration of the keys in this table.
      java.util.Set<K> keySet()
      Returns a Set view of the keys contained in this map.
      void purgeStaleEntries()
      Removes any stale entries whose keys have been finalized.
      V put​(K key, V value)
      Maps the specified key to the specified value in this table.
      void putAll​(java.util.Map<? extends K,​? extends V> m)
      Copies all of the mappings from the specified map to this one.
      V putIfAbsent​(K key, V value)
      V remove​(java.lang.Object key)
      Removes the key (and its corresponding value) from this map.
      boolean remove​(java.lang.Object key, java.lang.Object value)
      V replace​(K key, V value)
      boolean replace​(K key, V oldValue, V newValue)
      int size()
      Returns the number of key-value mappings in this map.
      java.util.Collection<V> values()
      Returns a Collection view of the values contained in this map.
      • Methods inherited from class java.util.AbstractMap

        clone, equals, hashCode, toString
      • Methods inherited from class java.lang.Object

        finalize, getClass, notify, notifyAll, wait, wait, wait
      • Methods inherited from interface java.util.concurrent.ConcurrentMap

        compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, replaceAll
      • Methods inherited from interface java.util.Map

        equals, hashCode
    • Constructor Detail

      • ConcurrentWeakKeyHashMap

        public ConcurrentWeakKeyHashMap​(int initialCapacity,
                                        float loadFactor,
                                        int concurrencyLevel)
        Creates a new, empty map with the specified initial capacity, load factor and concurrency level.
        Parameters:
        initialCapacity - the initial capacity. The implementation performs internal sizing to accommodate this many elements.
        loadFactor - the load factor threshold, used to control resizing. Resizing may be performed when the average number of elements per bin exceeds this threshold.
        concurrencyLevel - the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
        Throws:
        java.lang.IllegalArgumentException - if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
      • ConcurrentWeakKeyHashMap

        public ConcurrentWeakKeyHashMap​(int initialCapacity,
                                        float loadFactor)
        Creates a new, empty map with the specified initial capacity and load factor and with the default reference types (weak keys, strong values), and concurrencyLevel (16).
        Parameters:
        initialCapacity - The implementation performs internal sizing to accommodate this many elements.
        loadFactor - the load factor threshold, used to control resizing. Resizing may be performed when the average number of elements per bin exceeds this threshold.
        Throws:
        java.lang.IllegalArgumentException - if the initial capacity of elements is negative or the load factor is nonpositive
      • ConcurrentWeakKeyHashMap

        public ConcurrentWeakKeyHashMap​(int initialCapacity)
        Creates a new, empty map with the specified initial capacity, and with default reference types (weak keys, strong values), load factor (0.75) and concurrencyLevel (16).
        Parameters:
        initialCapacity - the initial capacity. The implementation performs internal sizing to accommodate this many elements.
        Throws:
        java.lang.IllegalArgumentException - if the initial capacity of elements is negative.
      • ConcurrentWeakKeyHashMap

        public ConcurrentWeakKeyHashMap()
        Creates a new, empty map with a default initial capacity (16), reference types (weak keys, strong values), default load factor (0.75) and concurrencyLevel (16).
      • ConcurrentWeakKeyHashMap

        public ConcurrentWeakKeyHashMap​(java.util.Map<? extends K,​? extends V> m)
        Creates a new map with the same mappings as the given map. The map is created with a capacity of 1.5 times the number of mappings in the given map or 16 (whichever is greater), and a default load factor (0.75) and concurrencyLevel (16).
        Parameters:
        m - the map
    • Method Detail

      • isEmpty

        public boolean isEmpty()
        Returns true if this map contains no key-value mappings.
        Specified by:
        isEmpty in interface java.util.Map<K,​V>
        Overrides:
        isEmpty in class java.util.AbstractMap<K,​V>
        Returns:
        true if this map contains no key-value mappings
      • size

        public int size()
        Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
        Specified by:
        size in interface java.util.Map<K,​V>
        Overrides:
        size in class java.util.AbstractMap<K,​V>
        Returns:
        the number of key-value mappings in this map
      • get

        public V get​(java.lang.Object key)
        Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

        More formally, if this map contains a mapping from a key k to a value v such that key.equals(k), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

        Specified by:
        get in interface java.util.Map<K,​V>
        Overrides:
        get in class java.util.AbstractMap<K,​V>
        Throws:
        java.lang.NullPointerException - if the specified key is null
      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Tests if the specified object is a key in this table.
        Specified by:
        containsKey in interface java.util.Map<K,​V>
        Overrides:
        containsKey in class java.util.AbstractMap<K,​V>
        Parameters:
        key - possible key
        Returns:
        true if and only if the specified object is a key in this table, as determined by the equals method; false otherwise.
        Throws:
        java.lang.NullPointerException - if the specified key is null
      • containsValue

        public boolean containsValue​(java.lang.Object value)
        Returns true if this map maps one or more keys to the specified value. Note: This method requires a full internal traversal of the hash table, and so is much slower than method containsKey.
        Specified by:
        containsValue in interface java.util.Map<K,​V>
        Overrides:
        containsValue in class java.util.AbstractMap<K,​V>
        Parameters:
        value - value whose presence in this map is to be tested
        Returns:
        true if this map maps one or more keys to the specified value
        Throws:
        java.lang.NullPointerException - if the specified value is null
      • contains

        public boolean contains​(java.lang.Object value)
        Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality to containsValue(java.lang.Object), and exists solely to ensure full compatibility with class Hashtable, which supported this method prior to introduction of the Java Collections framework.
        Parameters:
        value - a value to search for
        Returns:
        true if and only if some key maps to the value argument in this table as determined by the equals method; false otherwise
        Throws:
        java.lang.NullPointerException - if the specified value is null
      • put

        public V put​(K key,
                     V value)
        Maps the specified key to the specified value in this table. Neither the key nor the value can be null.

        The value can be retrieved by calling the get method with a key that is equal to the original key.

        Specified by:
        put in interface java.util.Map<K,​V>
        Overrides:
        put in class java.util.AbstractMap<K,​V>
        Parameters:
        key - key with which the specified value is to be associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with key, or null if there was no mapping for key
        Throws:
        java.lang.NullPointerException - if the specified key or value is null
      • putIfAbsent

        public V putIfAbsent​(K key,
                             V value)
        Specified by:
        putIfAbsent in interface java.util.concurrent.ConcurrentMap<K,​V>
        Specified by:
        putIfAbsent in interface java.util.Map<K,​V>
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        java.lang.NullPointerException - if the specified key or value is null
      • putAll

        public void putAll​(java.util.Map<? extends K,​? extends V> m)
        Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified map.
        Specified by:
        putAll in interface java.util.Map<K,​V>
        Overrides:
        putAll in class java.util.AbstractMap<K,​V>
        Parameters:
        m - mappings to be stored in this map
      • remove

        public V remove​(java.lang.Object key)
        Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the map.
        Specified by:
        remove in interface java.util.Map<K,​V>
        Overrides:
        remove in class java.util.AbstractMap<K,​V>
        Parameters:
        key - the key that needs to be removed
        Returns:
        the previous value associated with key, or null if there was no mapping for key
        Throws:
        java.lang.NullPointerException - if the specified key is null
      • remove

        public boolean remove​(java.lang.Object key,
                              java.lang.Object value)
        Specified by:
        remove in interface java.util.concurrent.ConcurrentMap<K,​V>
        Specified by:
        remove in interface java.util.Map<K,​V>
        Throws:
        java.lang.NullPointerException - if the specified key is null
      • replace

        public boolean replace​(K key,
                               V oldValue,
                               V newValue)
        Specified by:
        replace in interface java.util.concurrent.ConcurrentMap<K,​V>
        Specified by:
        replace in interface java.util.Map<K,​V>
        Throws:
        java.lang.NullPointerException - if any of the arguments are null
      • replace

        public V replace​(K key,
                         V value)
        Specified by:
        replace in interface java.util.concurrent.ConcurrentMap<K,​V>
        Specified by:
        replace in interface java.util.Map<K,​V>
        Returns:
        the previous value associated with the specified key, or null if there was no mapping for the key
        Throws:
        java.lang.NullPointerException - if the specified key or value is null
      • clear

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

        public void purgeStaleEntries()
        Removes any stale entries whose keys have been finalized. Use of this method is normally not necessary since stale entries are automatically removed lazily, when blocking operations are required. However, there are some cases where this operation should be performed eagerly, such as cleaning up old references to a ClassLoader in a multi-classloader environment.

        Note: this method will acquire locks, one at a time, across all segments of this table, so if it is to be used, it should be used sparingly.

      • keySet

        public java.util.Set<K> keySet()
        Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        Specified by:
        keySet in interface java.util.Map<K,​V>
        Overrides:
        keySet in class java.util.AbstractMap<K,​V>
      • values

        public java.util.Collection<V> values()
        Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        Specified by:
        values in interface java.util.Map<K,​V>
        Overrides:
        values in class java.util.AbstractMap<K,​V>
      • entrySet

        public java.util.Set<java.util.Map.Entry<K,​V>> entrySet()
        Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        Specified by:
        entrySet in interface java.util.Map<K,​V>
        Specified by:
        entrySet in class java.util.AbstractMap<K,​V>
      • keys

        public java.util.Enumeration<K> keys()
        Returns an enumeration of the keys in this table.
        Returns:
        an enumeration of the keys in this table
        See Also:
        keySet()
      • elements

        public java.util.Enumeration<V> elements()
        Returns an enumeration of the values in this table.
        Returns:
        an enumeration of the values in this table
        See Also:
        values()