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

Class ConcurrentHashMap

java.lang.Object
java.util.AbstractMap
org.apache.openjpa.lib.util.concurrent.ConcurrentHashMap
All Implemented Interfaces:
Serializable, Cloneable, Map, ConcurrentMap, SizedMap
public class ConcurrentHashMap extends AbstractMap implements ConcurrentMap, SizedMap, Cloneable, 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:

  • Constructor Details

    • 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:
      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:
      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(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:
      NullPointerException - if the specified map is null.

  • Method Details

    • 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(Object key, 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 Map
      Overrides:
      size in class 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 Map
      Overrides:
      isEmpty in class AbstractMap
      Returns:
      true if this map contains no key-value mappings.

    • get

      public Object get(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 Map
      Overrides:
      get in class 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:

    • containsKey

      public final boolean containsKey(Object key)
      Returns true if this map contains a mapping for the specified key.
      Specified by:
      containsKey in interface Map
      Overrides:
      containsKey in class 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(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 Object put(Object key, 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 Map
      Overrides:
      put in class 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 Object putIfAbsent(Object key, Object value)
      Specified by:
      putIfAbsent in interface Map

    • putAll

      public final void putAll(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 Map
      Overrides:
      putAll in class AbstractMap
      Parameters:
      t - mappings to be stored in this map.
      Throws:
      NullPointerException - if the specified map is null.

    • remove

      public Object remove(Object key)
      Removes the mapping for this key from this map if present.
      Specified by:
      remove in interface Map
      Overrides:
      remove in class 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 Map
      Overrides:
      clear in class AbstractMap

    • removeRandom

      public 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 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(Object value)
      Returns true if this map maps one or more keys to the specified value.
      Specified by:
      containsValue in interface Map
      Overrides:
      containsValue in class 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 Object clone()
      Returns a shallow copy of this ConcurrentHashMap instance: the keys and values themselves are not cloned.
      Overrides:
      clone in class AbstractMap
      Returns:
      a shallow copy of this map.

    • createEntry

      protected ConcurrentHashMap.Entry createEntry(int h, Object k, Object v, ConcurrentHashMap.Entry n)

    • keySet

      public final 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 Map
      Overrides:
      keySet in class AbstractMap
      Returns:
      a set view of the keys contained in this map.

    • values

      public final 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 Map
      Overrides:
      values in class AbstractMap
      Returns:
      a collection view of the values contained in this map.

    • entrySet

      public final 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 Map
      Specified by:
      entrySet in class AbstractMap
      Returns:
      a collection view of the mappings contained in this map.
      See Also: