Package org.apache.xbean.propertyeditor

Class ReferenceIdentityMap

  • All Implemented Interfaces:
    java.util.Map
    public class ReferenceIdentityMap
extends java.lang.Object
implements java.util.Map
    Streamlined version of a WeakIdentityHashMap. Provides Identity semantics with Weak References to keys. This allows proxies to be GC'ed when no longer referenced by clients. BasicProxymanager.destroyProxy() need not be invoked when a proxy is no longer needed. Note that this is not a full Map implementation. The iteration and collection capabilities of Map have been discarded to keep the implementation lightweight.

    Much of this code was cribbed from the Commons Collection 3.1 implementation of ReferenceIdentityMap and AbstractReferenceMap.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private static class  ReferenceIdentityMap.ReferenceEntry
      Each entry in the Map is represented with a ReferenceEntry.

      • 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
      private int calculateThreshold​(int newCapacity, float factor)
      Calculates the new threshold of the map, where it will be resized.
      private void checkCapacity()
      Checks the capacity of the map and enlarges it if necessary.
      void clear()
      Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
      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.
      private ReferenceIdentityMap.ReferenceEntry createEntry​(int index, int hashCode, java.lang.Object key, java.lang.Object value)
      Creates a new ReferenceEntry.
      private void ensureCapacity​(int newCapacity)
      Changes the size of the data structure to the capacity proposed.
      java.util.Set entrySet()  
      java.lang.Object get​(java.lang.Object key)
      Gets the value mapped to the key specified.
      private ReferenceIdentityMap.ReferenceEntry getEntry​(java.lang.Object key)
      Gets the entry mapped to the key specified.
      private int hash​(java.lang.Object key)
      Gets the hash code for the key specified.
      private int hashIndex​(int hashCode, int dataSize)
      Gets the index into the data storage for the hashCode specified.
      boolean isEmpty()
      Checks whether the map is currently empty.
      java.util.Set keySet()  
      private void purge()
      Purges stale mappings from this map.
      private void purge​(java.lang.ref.Reference purgedEntry)
      Purges the specified reference.
      java.lang.Object put​(java.lang.Object key, java.lang.Object value)
      Puts a key-value entry into this map.
      void putAll​(java.util.Map t)  
      java.lang.Object remove​(java.lang.Object key)
      Removes the specified mapping from this map.
      private void removeEntry​(ReferenceIdentityMap.ReferenceEntry entry, int hashIndex, ReferenceIdentityMap.ReferenceEntry previous)
      Removes an entry from the chain stored in a particular index.
      int size()
      Gets the size of the map.
      java.util.Collection values()  

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

      • Methods inherited from interface java.util.Map

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

    • Field Detail

      • DEFAULT_CAPACITY

        private static final int DEFAULT_CAPACITY
        The default capacity to use. Always use a power of 2!!!
        See Also:
        Constant Field Values

      • DEFAULT_LOAD_FACTOR

        private static final float DEFAULT_LOAD_FACTOR
        The default load factor to use
        See Also:
        Constant Field Values

      • MAXIMUM_CAPACITY

        private static final int MAXIMUM_CAPACITY
        The maximum capacity allowed
        See Also:
        Constant Field Values

      • loadFactor

        private float loadFactor
        Load factor, normally 0.75

      • size

        private transient int size
        The size of the map

      • threshold

        private transient int threshold
        Size at which to rehash

      • purgeQueue

        private java.lang.ref.ReferenceQueue purgeQueue
        ReferenceQueue used to eliminate GC'ed entries.

    • Constructor Detail

      • ReferenceIdentityMap

        public ReferenceIdentityMap()

    • Method Detail

      • size

        public int size()
        Gets the size of the map.
        Specified by:
        size in interface java.util.Map
        Returns:
        the size

      • isEmpty

        public boolean isEmpty()
        Checks whether the map is currently empty.
        Specified by:
        isEmpty in interface java.util.Map
        Returns:
        true if the map is currently size zero

      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Checks whether the map contains the specified key.
        Specified by:
        containsKey in interface java.util.Map
        Parameters:
        key - the key to search for
        Returns:
        true if the map contains the key

      • containsValue

        public boolean containsValue​(java.lang.Object value)
        Checks whether the map contains the specified value.
        Specified by:
        containsValue in interface java.util.Map
        Parameters:
        value - the value to search for
        Returns:
        true if the map contains the value

      • get

        public java.lang.Object get​(java.lang.Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface java.util.Map
        Parameters:
        key - the key
        Returns:
        the mapped value, null if no match

      • put

        public java.lang.Object put​(java.lang.Object key,
                            java.lang.Object value)
        Puts a key-value entry into this map. Neither the key nor the value may be null.
        Specified by:
        put in interface java.util.Map
        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

      • remove

        public java.lang.Object remove​(java.lang.Object key)
        Removes the specified mapping from this map.
        Specified by:
        remove in interface java.util.Map
        Parameters:
        key - the mapping to remove
        Returns:
        the value mapped to the removed key, null if key not in map

      • clear

        public void clear()
        Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
        Specified by:
        clear in interface java.util.Map

      • values

        public java.util.Collection values()
        Specified by:
        values in interface java.util.Map

      • putAll

        public void putAll​(java.util.Map t)
        Specified by:
        putAll in interface java.util.Map

      • entrySet

        public java.util.Set entrySet()
        Specified by:
        entrySet in interface java.util.Map

      • keySet

        public java.util.Set keySet()
        Specified by:
        keySet in interface java.util.Map

      • getEntry

        private ReferenceIdentityMap.ReferenceEntry getEntry​(java.lang.Object key)
        Gets the entry mapped to the key specified.
        Parameters:
        key - the key
        Returns:
        the entry, null if no match

      • createEntry

        private ReferenceIdentityMap.ReferenceEntry createEntry​(int index,
                                                        int hashCode,
                                                        java.lang.Object key,
                                                        java.lang.Object value)
        Creates a new ReferenceEntry.
        Parameters:
        index - the index into the data map
        hashCode - the hash code for the new entry
        key - the key to store
        value - the value to store
        Returns:
        the newly created entry

      • removeEntry

        private void removeEntry​(ReferenceIdentityMap.ReferenceEntry entry,
                         int hashIndex,
                         ReferenceIdentityMap.ReferenceEntry previous)
        Removes an entry from the chain stored in a particular index.

        This implementation removes the entry from the data storage table. The size is not updated.

        Parameters:
        entry - the entry to remove
        hashIndex - the index into the data structure
        previous - the previous entry in the chain

      • checkCapacity

        private void checkCapacity()
        Checks the capacity of the map and enlarges it if necessary.

        This implementation uses the threshold to check if the map needs enlarging

      • ensureCapacity

        private void ensureCapacity​(int newCapacity)
        Changes the size of the data structure to the capacity proposed.
        Parameters:
        newCapacity - the new capacity of the array (a power of two, less or equal to max)

      • calculateThreshold

        private int calculateThreshold​(int newCapacity,
                               float factor)
        Calculates the new threshold of the map, where it will be resized. This implementation uses the load factor.
        Parameters:
        newCapacity - the new capacity
        factor - the load factor
        Returns:
        the new resize threshold

      • hash

        private int hash​(java.lang.Object key)
        Gets the hash code for the key specified.

        This implementation uses the identity hash code.

        Parameters:
        key - the key to get a hash code for
        Returns:
        the hash code

      • hashIndex

        private int hashIndex​(int hashCode,
                      int dataSize)
        Gets the index into the data storage for the hashCode specified. This implementation uses the least significant bits of the hashCode.
        Parameters:
        hashCode - the hash code to use
        dataSize - the size of the data to pick a bucket from
        Returns:
        the bucket index

      • purge

        private void purge()
        Purges stale mappings from this map.

        Note that this method is not synchronized! Special care must be taken if, for instance, you want stale mappings to be removed on a periodic basis by some background thread.

      • purge

        private void purge​(java.lang.ref.Reference purgedEntry)
        Purges the specified reference.
        Parameters:
        purgedEntry - the reference to purge