org.jboss.util.collection

Class WeakIdentityHashMap

java.lang.Object

org.jboss.util.collection.WeakIdentityHashMap

All Implemented Interfaces:

java.util.Map

public class WeakIdentityHashMap
extends java.lang.Object
implements java.util.Map

A hashtable-based Map implementation with weak keys and using reference-equality in place of object-equality when comparing keys (and values). In an WeakIdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1==k2). An entry in a WeakIdentityHashMap will automatically be removed when its key is no longer in ordinary use. More precisely, the presence of a mapping for a given key will not prevent the key from being discarded by the garbage collector, that is, made finalizable, finalized, and then reclaimed. When a key has been discarded its entry is effectively removed from the map.

Based on java.util.WeakHashMap

Version:

$Revision$

See Also:

IdentityHashMap, WeakHashMap

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	WeakIdentityHashMap.Entry The entries in this hash table extend WeakReference, using its main ref field as the key.
private class	WeakIdentityHashMap.EntryIterator
private class	WeakIdentityHashMap.EntrySet
private class	WeakIdentityHashMap.HashIterator
private class	WeakIdentityHashMap.KeyIterator
private class	WeakIdentityHashMap.KeySet
(package private) static class	WeakIdentityHashMap.SimpleEntry
private class	WeakIdentityHashMap.ValueIterator
private class	WeakIdentityHashMap.Values

Field Summary

Fields

Modifier and Type	Field and Description
private static int	DEFAULT_INITIAL_CAPACITY The default initial capacity -- MUST be a power of two.
private static float	DEFAULT_LOAD_FACTOR The load fast used when none specified in constructor.
private java.util.Set	entrySet
(package private) java.util.Set	keySet Each of these fields are initialized to contain an instance of the appropriate view the first time this view is requested.
private float	loadFactor The load factor for the hash table.
private static int	MAXIMUM_CAPACITY The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments.
private int	modCount The number of times this HashMap has been structurally modified Structural modifications are those that change the number of mappings in the HashMap or otherwise modify its internal structure (e.g., rehash).
private static java.lang.Object	NULL_KEY Value representing null keys inside tables.
private java.lang.ref.ReferenceQueue	queue Reference queue for cleared WeakEntries
private int	size The number of key-value mappings contained in this weak hash map.
private WeakIdentityHashMap.Entry[]	table The table, resized as necessary.
private int	threshold The next size value at which to resize (capacity * load factor).
(package private) java.util.Collection	values

Constructor Summary

Constructors

Constructor and Description
WeakIdentityHashMap() Constructs a new, empty WeakIdentityHashMap with the default initial capacity (16) and the default load factor (0.75).
WeakIdentityHashMap(int initialCapacity) Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the default load factor, which is 0.75.
WeakIdentityHashMap(int initialCapacity, float loadFactor) Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the given load factor.
WeakIdentityHashMap(java.util.Map t) Constructs a new WeakIdentityHashMap with the same mappings as the specified Map.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all mappings from this map.
boolean	containsKey(java.lang.Object key) Returns true if this map contains a mapping for the specified key.
private boolean	containsNullValue() Special-case code for containsValue with null argument
boolean	containsValue(java.lang.Object value) Returns true if this map maps one or more keys to the specified value.
java.util.Set	entrySet() Returns a collection view of the mappings contained in this map.
private void	expungeStaleEntries() Expunge stale entries from the table.
java.lang.Object	get(java.lang.Object key) Returns the value to which the specified key is mapped in this weak hash map, or null if the map contains no mapping for this key.
(package private) WeakIdentityHashMap.Entry	getEntry(java.lang.Object key) Returns the entry associated with the specified key in the HashMap.
private WeakIdentityHashMap.Entry[]	getTable() Return the table after first expunging stale entries
(package private) int	hash(java.lang.Object x) Return a hash code for non-null Object x.
(package private) static int	indexFor(int h, int length) Return index for hash code h.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
java.util.Set	keySet() Returns a set view of the keys contained in this map.
private static java.lang.Object	maskNull(java.lang.Object key) Use NULL_KEY for key if it is null.
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	remove(java.lang.Object key) Removes the mapping for this key from this map if present.
(package private) WeakIdentityHashMap.Entry	removeMapping(java.lang.Object o) Special version of remove needed by Entry set
(package private) void	resize(int newCapacity) Rehashes the contents of this map into a new HashMap instance with a larger capacity.
int	size() Returns the number of key-value mappings in this map.
private void	transfer(WeakIdentityHashMap.Entry[] src, WeakIdentityHashMap.Entry[] dest) Transfer all entries from src to dest tables
private static java.lang.Object	unmaskNull(java.lang.Object key) Return internal representation of null key back to caller as null
java.util.Collection	values() Returns a collection view of the values contained in this map.

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_INITIAL_CAPACITY

private static final int DEFAULT_INITIAL_CAPACITY

The default initial capacity -- MUST be a power of two.

See Also:

Constant Field Values

MAXIMUM_CAPACITY

private static final int MAXIMUM_CAPACITY

The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments. MUST be a power of two <= 1<<30.

See Also:

Constant Field Values

DEFAULT_LOAD_FACTOR

private static final float DEFAULT_LOAD_FACTOR

The load fast used when none specified in constructor.

See Also:

Constant Field Values

table

private WeakIdentityHashMap.Entry[] table

The table, resized as necessary. Length MUST Always be a power of two.

size

private int size

The number of key-value mappings contained in this weak hash map.

threshold

private int threshold

The next size value at which to resize (capacity * load factor).

loadFactor

private final float loadFactor

The load factor for the hash table.

queue

private final java.lang.ref.ReferenceQueue queue

Reference queue for cleared WeakEntries

modCount

private volatile int modCount

The number of times this HashMap has been structurally modified Structural modifications are those that change the number of mappings in the HashMap or otherwise modify its internal structure (e.g., rehash). This field is used to make iterators on Collection-views of the HashMap fail-fast. (See ConcurrentModificationException).

keySet

transient volatile java.util.Set keySet

Each of these fields are initialized to contain an instance of the appropriate view the first time this view is requested. The views are stateless, so there's no reason to create more than one of each.

values

transient volatile java.util.Collection values

NULL_KEY

private static final java.lang.Object NULL_KEY

Value representing null keys inside tables.

entrySet

private transient java.util.Set entrySet

Constructor Detail

WeakIdentityHashMap

public WeakIdentityHashMap(int initialCapacity,
                           float loadFactor)

Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the given load factor.

Parameters:

initialCapacity - The initial capacity of the WeakIdentityHashMap

loadFactor - The load factor of the WeakIdentityHashMap

Throws:

java.lang.IllegalArgumentException - If the initial capacity is negative, or if the load factor is nonpositive.

WeakIdentityHashMap

public WeakIdentityHashMap(int initialCapacity)

Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the default load factor, which is 0.75.

Parameters:

initialCapacity - The initial capacity of the WeakIdentityHashMap

Throws:

java.lang.IllegalArgumentException - If the initial capacity is negative.

WeakIdentityHashMap

public WeakIdentityHashMap()

Constructs a new, empty WeakIdentityHashMap with the default initial capacity (16) and the default load factor (0.75).

WeakIdentityHashMap

public WeakIdentityHashMap(java.util.Map t)

Constructs a new WeakIdentityHashMap with the same mappings as the specified Map. The WeakIdentityHashMap is created with default load factor, which is 0.75 and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters:

t - the map whose mappings are to be placed in this map.

Throws:

java.lang.NullPointerException - if the specified map is null.

Method Detail

maskNull

private static java.lang.Object maskNull(java.lang.Object key)

Use NULL_KEY for key if it is null.

unmaskNull

private static java.lang.Object unmaskNull(java.lang.Object key)

Return internal representation of null key back to caller as null

hash

int hash(java.lang.Object x)

Return a hash code for non-null Object x.

indexFor

static int indexFor(int h,
                    int length)

Return index for hash code h.

expungeStaleEntries

private void expungeStaleEntries()

Expunge stale entries from the table.

getTable

private WeakIdentityHashMap.Entry[] getTable()

Return the table after first expunging stale entries

size

public int size()

Returns the number of key-value mappings in this map. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.

Specified by:

size in interface java.util.Map

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.

Specified by:

isEmpty in interface java.util.Map

get

public java.lang.Object get(java.lang.Object key)

Returns the value to which the specified key is mapped in this weak 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

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 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

Parameters:

key - The key whose presence in this map is to be tested

Returns:

true if there is a mapping for key; false otherwise

getEntry

WeakIdentityHashMap.Entry getEntry(java.lang.Object key)

Returns the entry associated with the specified key in the HashMap. Returns null if the HashMap 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

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 HashMap previously associated null with the specified key.

resize

void resize(int newCapacity)

Rehashes the contents of this map into a new HashMap instance with a larger capacity. This method is called automatically when the number of keys in this map exceeds its capacity and load factor. Note that this method is a no-op if it's called with newCapacity == 2*MAXIMUM_CAPACITY (which is Integer.MIN_VALUE).

Parameters:

newCapacity - the new capacity, MUST be a power of two.

transfer

private void transfer(WeakIdentityHashMap.Entry[] src,
                      WeakIdentityHashMap.Entry[] dest)

Transfer all entries from src to dest tables

putAll

public 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

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

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.

removeMapping

WeakIdentityHashMap.Entry removeMapping(java.lang.Object o)

Special version of remove needed by Entry set

clear

public void clear()

Removes all mappings from this map.

Specified by:

clear in interface java.util.Map

containsValue

public 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

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.

containsNullValue

private boolean containsNullValue()

Special-case code for containsValue with null argument

keySet

public 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

Returns:

a set view of the keys contained in this map.

values

public 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

Returns:

a collection view of the values contained in this map.

entrySet

public 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

Returns:

a collection view of the mappings contained in this map.

See Also:

Map.Entry