Package com.globalmentor.collections
Class AbstractPurgeOnWriteReferenceValueMap<K,V,R extends java.lang.ref.Reference<V> & AbstractPurgeOnWriteReferenceValueMap.Keyed<K>>
- java.lang.Object
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- com.globalmentor.collections.AbstractPurgeOnWriteReferenceValueMap<K,V,R>
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- Type Parameters:
K
- The type of key.V
- The type of value.R
- The type of reference.
- All Implemented Interfaces:
java.util.Map<K,V>
- Direct Known Subclasses:
PurgeOnWriteSoftValueHashMap
,PurgeOnWriteWeakValueHashMap
public abstract class AbstractPurgeOnWriteReferenceValueMap<K,V,R extends java.lang.ref.Reference<V> & AbstractPurgeOnWriteReferenceValueMap.Keyed<K>> extends java.lang.Object implements java.util.Map<K,V>
A map that uses references to store map values. Cleared references are only purged when map write operations occur.null
values are not supported.- Author:
- Garret Wilson
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Nested Class Summary
Nested Classes Modifier and Type Class Description protected static interface
AbstractPurgeOnWriteReferenceValueMap.Keyed<K>
An object that remembers the key associated with it.
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Constructor Summary
Constructors Constructor Description AbstractPurgeOnWriteReferenceValueMap(java.util.Map<K,R> map)
Decorated map constructor.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description void
clear()
Removes all mappings from this map (optional operation).boolean
containsKey(java.lang.Object key)
Returnstrue
if this map contains a mapping for the specified key.boolean
containsValue(java.lang.Object value)
Returnstrue
if this map maps one or more keys to the specified value.protected abstract R
createReference(K key, V value, java.lang.ref.ReferenceQueue<V> referenceQueue)
Creates the appropriate reference for associating the given value with the given key.java.util.Set<java.util.Map.Entry<K,V>>
entrySet()
Returns a set view of the mappings contained in this map.boolean
equals(java.lang.Object o)
Compares the specified object with this map for equality.V
get(java.lang.Object key)
Returns the value to which this map maps the specified key.int
hashCode()
Returns the hash code value for this map.boolean
isEmpty()
Returnstrue
if this map contains no key-value mappings.java.util.Set<K>
keySet()
Returns a set view of the keys contained in this map.void
purge()
Purges all enqueued references.protected void
purgeExcept(R exceptReference)
Purges all enqueued references except for the given reference.V
put(K key, V value)
Associates the specified value with the specified key in this map (optional operation).void
putAll(java.util.Map<? extends K,? extends V> t)
Copies all of the mappings from the specified map to this map (optional operation).V
remove(java.lang.Object key)
Removes the mapping for this key from this map if it is present (optional operation).int
size()
Returns the number of key-value mappings in this map.java.util.Collection<V>
values()
Returns a collection view of the values contained in this map.
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Method Detail
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size
public int size()
Returns the number of key-value mappings in this map. If the map contains more thanInteger.MAX_VALUE
elements, returnsInteger.MAX_VALUE
.
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isEmpty
public boolean isEmpty()
Returnstrue
if this map contains no key-value mappings.
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containsKey
public boolean containsKey(java.lang.Object key)
Returnstrue
if this map contains a mapping for the specified key. More formally, returnstrue
if and only if this map contains a mapping for a keyk
such that(key==null ? k==null : key.equals(k))
. (There can be at most one such mapping.)- Specified by:
containsKey
in interfacejava.util.Map<K,V>
- Parameters:
key
- key whose presence in this map is to be tested.- Returns:
true
if this map contains a mapping for the specified key.- Throws:
java.lang.ClassCastException
- if the key is of an inappropriate type for this map (optional).java.lang.NullPointerException
- if the key isnull
and this map does not permitnull
keys (optional).
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containsValue
public boolean containsValue(java.lang.Object value)
Returnstrue
if this map maps one or more keys to the specified value. More formally, returnstrue
if and only if this map contains at least one mapping to a valuev
such that(value==null ? v==null : value.equals(v))
. This operation will probably require time linear in the map size for most implementations of theMap
interface.- Specified by:
containsValue
in interfacejava.util.Map<K,V>
- 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.- Throws:
java.lang.ClassCastException
- if the value is of an inappropriate type for this map (optional).java.lang.NullPointerException
- if the value isnull
and this map does not permitnull
values (optional).
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get
public V get(java.lang.Object key)
Returns the value to which this map maps the specified key. Returnsnull
if the map contains no mapping for this key. A return value ofnull
does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key tonull
. ThecontainsKey
operation may be used to distinguish these two cases.More formally, if this map contains a mapping from a key
k
to a valuev
such that(key==null ? k==null : key.equals(k))
, then this method returnsv
; otherwise it returnsnull
. (There can be at most one such mapping.)- Specified by:
get
in interfacejava.util.Map<K,V>
- Parameters:
key
- 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. - Throws:
java.lang.ClassCastException
- if the key is of an inappropriate type for this map (optional).java.lang.NullPointerException
- if the key isnull
and this map does not permitnull
keys (optional).- See Also:
containsKey(Object)
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put
public V put(K key, V value)
Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A mapm
is said to contain a mapping for a keyk
if and only ifm.containsKey(k)
would returntrue
.))- Specified by:
put
in interfacejava.util.Map<K,V>
- 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. Anull
return can also indicate that the map previously associatednull
with the specified key, if the implementation supportsnull
values. - Throws:
java.lang.UnsupportedOperationException
- if theput
operation is not supported by this map.java.lang.ClassCastException
- if the class of the specified key or value prevents it from being stored in this map.java.lang.IllegalArgumentException
- if some aspect of this key or value prevents it from being stored in this map.java.lang.NullPointerException
- if this map does not permitnull
keys or values, and the specified key or value isnull
.
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remove
public V remove(java.lang.Object key)
Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from keyk
to valuev
such that(key==null ? k==null : key.equals(k))
, that mapping is removed. (The map can contain at most one such mapping.)Returns the value to which the map previously associated the key, or
null
if the map contained no mapping for this key. (Anull
return can also indicate that the map previously associatednull
with the specified key if the implementation supportsnull
values.) The map will not contain a mapping for the specified key once the call returns.- Specified by:
remove
in interfacejava.util.Map<K,V>
- 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. - Throws:
java.lang.ClassCastException
- if the key is of an inappropriate type for this map (optional).java.lang.NullPointerException
- if the key isnull
and this map does not permitnull
keys (optional).java.lang.UnsupportedOperationException
- if theremove
method is not supported by this map.
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putAll
public void putAll(java.util.Map<? extends K,? extends V> t)
Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of callingput(k, v)
on this map once for each mapping from keyk
to valuev
in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.- Specified by:
putAll
in interfacejava.util.Map<K,V>
- Parameters:
t
- Mappings to be stored in this map.- Throws:
java.lang.UnsupportedOperationException
- if theputAll
method is not supported by this map.java.lang.ClassCastException
- if the class of a key or value in the specified map prevents it from being stored in this map.java.lang.IllegalArgumentException
- some aspect of a key or value in the specified map prevents it from being stored in this map.java.lang.NullPointerException
- if the specified map isnull
, or if this map does not permitnull
keys or values, and the specified map containsnull
keys or values.
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clear
public void clear()
Removes all mappings from this map (optional operation).
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keySet
public java.util.Set<K> 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. If the map is modified while an iteration over the set is in progress (except through the iterator's ownremove
operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via theIterator.remove
,Set.remove
,removeAll
retainAll
, andclear
operations. It does not support the add oraddAll
operations.
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values
public java.util.Collection<V> 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. If the map is modified while an iteration over the collection is in progress (except through the iterator's ownremove
operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via theIterator.remove
,Collection.remove
,removeAll
,retainAll
andclear
operations. It does not support the add oraddAll
operations.
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entrySet
public java.util.Set<java.util.Map.Entry<K,V>> entrySet()
Returns a set view of the mappings contained in this map. Each element in the returned set is aMap.Entry
. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's ownremove
operation, or through thesetValue
operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via theIterator.remove
,Set.remove
,removeAll
,retainAll
andclear
operations. It does not support theadd
oraddAll
operations.
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equals
public boolean equals(java.lang.Object o)
Compares the specified object with this map for equality. Returnstrue
if the given object is also a map and the two Maps represent the same mappings. More formally, two mapst1
andt2
represent the same mappings ift1.entrySet().equals(t2.entrySet())
. This ensures that theequals
method works properly across different implementations of theMap
interface.
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hashCode
public int hashCode()
Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hashCodes of each entry in the map's entrySet view. This ensures thatt1.equals(t2)
implies thatt1.hashCode()==t2.hashCode()
for any two mapst1
andt2
, as required by the general contract of Object.hashCode.- Specified by:
hashCode
in interfacejava.util.Map<K,V>
- Overrides:
hashCode
in classjava.lang.Object
- Returns:
- the hash code value for this map.
- See Also:
Map.Entry.hashCode()
,Object.hashCode()
,Object.equals(Object)
,equals(Object)
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purge
public void purge()
Purges all enqueued references.
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purgeExcept
protected void purgeExcept(R exceptReference)
Purges all enqueued references except for the given reference.- Parameters:
exceptReference
- The reference not to purge, ornull
if all enqueued references should be purged.
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createReference
protected abstract R createReference(K key, V value, java.lang.ref.ReferenceQueue<V> referenceQueue)
Creates the appropriate reference for associating the given value with the given key. The reference will be registered with the given queue.- Parameters:
key
- The key with which the value is being associated.value
- The value to be stored.referenceQueue
- The queue with which the reference will be registered.- Returns:
- A reference to the given value that also indicates the key being used.
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