Package 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 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 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 WeakEntriesprivate 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 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
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method 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 argumentboolean
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 tablesprivate static java.lang.Object
unmaskNull(java.lang.Object key)
Return internal representation of null key back to caller as nulljava.util.Collection
values()
Returns a collection view of the values contained in this map.
-
-
-
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 WeakIdentityHashMaploadFactor
- 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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.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 interfacejava.util.Map
- Returns:
- a collection view of the mappings contained in this map.
- See Also:
Map.Entry
-
-