Package org.apache.openjpa.lib.util.concurrent

Class ConcurrentHashMap

  • All Implemented Interfaces:
    java.io.Serializable, java.lang.Cloneable, java.util.Map, ConcurrentMap, SizedMap
    public class ConcurrentHashMap
extends java.util.AbstractMap
implements ConcurrentMap, SizedMap, java.lang.Cloneable, java.io.Serializable
    This class implements a HashMap which has limited synchronization. In particular mutators are generally synchronized while accessors are generally not. Additionally the Iterators returned by this class are not "fail-fast", but instead try to continue to iterate over the data structure after changes have been made. The synchronization semantics are built right in to the implementation rather than using a delegating wrapper like the other collection classes do because it wasn't clear to me that the how the two should be seperated or that it would be useful to do so. This can probably be a topic for further debate in the future. This class is based heavily on the HashMap class in the Java collections package.
    See Also:
    Serialized Form

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      protected static class  ConcurrentHashMap.Entry  

      • 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>

    • Constructor Summary

      Constructors 
      Constructor Description
      ConcurrentHashMap()
      Constructs an empty ConcurrentHashMap with the default initial capacity(16) and the default load factor(0.75).
      ConcurrentHashMap​(int initialCapacity)
      Constructs an empty ConcurrentHashMap with the specified initial capacity and the default load factor(0.75).
      ConcurrentHashMap​(int initialCapacity, float loadFactor)
      Constructs an empty ConcurrentHashMap with the specified initial capacity and load factor.
      ConcurrentHashMap​(java.util.Map m)
      Constructs a new ConcurrentHashMap with the same mappings as the specified Map.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      int capacity()
      Returns the current capacity of backing table in this map.
      void clear()
      Removes all mappings from this map.
      java.lang.Object clone()
      Returns a shallow copy of this ConcurrentHashMap instance: the keys and values themselves are not cloned.
      boolean containsKey​(java.lang.Object key)
      Returns true if this map contains a mapping for the specified key.
      boolean containsValue​(java.lang.Object value)
      Returns true if this map maps one or more keys to the specified value.
      protected ConcurrentHashMap.Entry createEntry​(int h, java.lang.Object k, java.lang.Object v, ConcurrentHashMap.Entry n)  
      java.util.Set entrySet()
      Returns a collection view of the mappings contained in this map.
      java.lang.Object get​(java.lang.Object key)
      Returns the value to which the specified key is mapped in this identity hash map, or null if the map contains no mapping for this key.
      protected ConcurrentHashMap.Entry getEntry​(java.lang.Object key)
      Returns the entry associated with the specified key in the ConcurrentHashMap.
      int getMaxSize()
      The maximum number of entries, or Integer.MAX_VALUE for no limit.
      boolean isEmpty()
      Returns true if this map contains no key-value mappings.
      boolean isFull()
      Whether the map is full.
      java.util.Set keySet()
      Returns a set view of the keys contained in this map.
      float loadFactor()
      Returns the load factor for this map.
      void overflowRemoved​(java.lang.Object key, java.lang.Object value)
      Overridable callback for when an overflow entry is automatically removed.
      java.lang.Object put​(java.lang.Object key, java.lang.Object value)
      Associates the specified value with the specified key in this map.
      void putAll​(java.util.Map t)
      Copies all of the mappings from the specified map to this map These mappings will replace any mappings that this map had for any of the keys currently in the specified map.
      java.lang.Object putIfAbsent​(java.lang.Object key, java.lang.Object value)  
      java.util.Iterator randomEntryIterator()
      Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
      java.lang.Object remove​(java.lang.Object key)
      Removes the mapping for this key from this map if present.
      java.util.Map.Entry removeRandom()
      Remove an arbitrary(not strictly random) entry from the map.
      void setMaxSize​(int maxSize)
      The maximum number of entries, or Integer.MAX_VALUE for no limit.
      int size()
      Returns the number of key-value mappings in this map.
      java.util.Collection values()
      Returns a collection view of the values contained in this map.

      • Methods inherited from class java.util.AbstractMap

        equals, hashCode, toString

      • Methods inherited from class java.lang.Object

        finalize, getClass, notify, notifyAll, wait, wait, wait

      • Methods inherited from interface java.util.Map

        compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, remove, replace, replace, replaceAll

    • Constructor Detail

      • ConcurrentHashMap

        public ConcurrentHashMap​(int initialCapacity,
                         float loadFactor)
        Constructs an empty ConcurrentHashMap with the specified initial capacity and load factor.
        Parameters:
        initialCapacity - The initial capacity.
        loadFactor - The load factor.
        Throws:
        java.lang.IllegalArgumentException - if the initial capacity is negative or the load factor is nonpositive.

      • ConcurrentHashMap

        public ConcurrentHashMap​(int initialCapacity)
        Constructs an empty ConcurrentHashMap with the specified initial capacity and the default load factor(0.75).
        Parameters:
        initialCapacity - the initial capacity.
        Throws:
        java.lang.IllegalArgumentException - if the initial capacity is negative.

      • ConcurrentHashMap

        public ConcurrentHashMap()
        Constructs an empty ConcurrentHashMap with the default initial capacity(16) and the default load factor(0.75).

      • ConcurrentHashMap

        public ConcurrentHashMap​(java.util.Map m)
        Constructs a new ConcurrentHashMap with the same mappings as the specified Map. The ConcurrentHashMap is created with default load factor(0.75) and an initial capacity sufficient to hold the mappings in the specified Map.
        Parameters:
        m - the map whose mappings are to be placed in this map.
        Throws:
        java.lang.NullPointerException - if the specified map is null.

    • Method Detail

      • capacity

        public final int capacity()
        Returns the current capacity of backing table in this map.
        Returns:
        the current capacity of backing table in this map.

      • loadFactor

        public final float loadFactor()
        Returns the load factor for this map.
        Returns:
        the load factor for this map.

      • getMaxSize

        public int getMaxSize()
        Description copied from interface: SizedMap
        The maximum number of entries, or Integer.MAX_VALUE for no limit.
        Specified by:
        getMaxSize in interface SizedMap

      • setMaxSize

        public void setMaxSize​(int maxSize)
        Description copied from interface: SizedMap
        The maximum number of entries, or Integer.MAX_VALUE for no limit.
        Specified by:
        setMaxSize in interface SizedMap

      • isFull

        public boolean isFull()
        Description copied from interface: SizedMap
        Whether the map is full.
        Specified by:
        isFull in interface SizedMap

      • overflowRemoved

        public void overflowRemoved​(java.lang.Object key,
                            java.lang.Object value)
        Description copied from interface: SizedMap
        Overridable callback for when an overflow entry is automatically removed.
        Specified by:
        overflowRemoved in interface SizedMap

      • size

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

      • isEmpty

        public final boolean isEmpty()
        Returns true if this map contains no key-value mappings.
        Specified by:
        isEmpty in interface java.util.Map
        Overrides:
        isEmpty in class java.util.AbstractMap
        Returns:
        true if this map contains no key-value mappings.

      • get

        public java.lang.Object get​(java.lang.Object key)
        Returns the value to which the specified key is mapped in this identity hash map, or null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it is also possible that the map explicitly maps the key to null. The containsKey method may be used to distinguish these two cases.
        Specified by:
        get in interface java.util.Map
        Overrides:
        get in class java.util.AbstractMap
        Parameters:
        key - the key whose associated value is to be returned.
        Returns:
        the value to which this map maps the specified key, or null if the map contains no mapping for this key.
        See Also:
        put(Object, Object)

      • containsKey

        public final boolean containsKey​(java.lang.Object key)
        Returns 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.AbstractMap
        Parameters:
        key - The key whose presence in this map is to be tested
        Returns:
        true if this map contains a mapping for the specified key.

      • getEntry

        protected ConcurrentHashMap.Entry getEntry​(java.lang.Object key)
        Returns the entry associated with the specified key in the ConcurrentHashMap. Returns null if the ConcurrentHashMap contains no mapping for this key.

      • put

        public java.lang.Object put​(java.lang.Object key,
                            java.lang.Object value)
        Associates 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.
        Specified by:
        put in interface java.util.Map
        Overrides:
        put in class java.util.AbstractMap
        Parameters:
        key - key with which the specified value is to be associated.
        value - value to be associated with the specified key.
        Returns:
        previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the ConcurrentHashMap previously associated null with the specified key.

      • putIfAbsent

        public java.lang.Object putIfAbsent​(java.lang.Object key,
                                    java.lang.Object value)
        Specified by:
        putIfAbsent in interface java.util.Map

      • putAll

        public final void putAll​(java.util.Map t)
        Copies all of the mappings from the specified map to this map These mappings will 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
        Overrides:
        putAll in class java.util.AbstractMap
        Parameters:
        t - mappings to be stored in this map.
        Throws:
        java.lang.NullPointerException - if the specified map is null.

      • remove

        public java.lang.Object remove​(java.lang.Object key)
        Removes the mapping for this key from this map if present.
        Specified by:
        remove in interface java.util.Map
        Overrides:
        remove in class java.util.AbstractMap
        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 mapping for key. A null return can also indicate that the map previously associated null with the specified key.

      • clear

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

      • removeRandom

        public java.util.Map.Entry removeRandom()
        Description copied from interface: ConcurrentMap
        Remove an arbitrary(not strictly random) entry from the map. This allows implementation of concurrent caches with size ceilings.
        Specified by:
        removeRandom in interface ConcurrentMap
        Returns:
        the removed entry, or null if map is empty

      • randomEntryIterator

        public java.util.Iterator randomEntryIterator()
        Description copied from interface: ConcurrentMap
        Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
        Specified by:
        randomEntryIterator in interface ConcurrentMap

      • containsValue

        public final boolean containsValue​(java.lang.Object value)
        Returns true if this map maps one or more keys to the specified value.
        Specified by:
        containsValue in interface java.util.Map
        Overrides:
        containsValue in class java.util.AbstractMap
        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.

      • clone

        public final java.lang.Object clone()
        Returns a shallow copy of this ConcurrentHashMap instance: the keys and values themselves are not cloned.
        Overrides:
        clone in class java.util.AbstractMap
        Returns:
        a shallow copy of this map.

      • keySet

        public final java.util.Set 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.
        Specified by:
        keySet in interface java.util.Map
        Overrides:
        keySet in class java.util.AbstractMap
        Returns:
        a set view of the keys contained in this map.

      • values

        public final java.util.Collection 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.
        Specified by:
        values in interface java.util.Map
        Overrides:
        values in class java.util.AbstractMap
        Returns:
        a collection view of the values contained in this map.

      • entrySet

        public final java.util.Set entrySet()
        Returns a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry. 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 the map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.
        Specified by:
        entrySet in interface java.util.Map
        Specified by:
        entrySet in class java.util.AbstractMap
        Returns:
        a collection view of the mappings contained in this map.
        See Also:
        Map.Entry