public class WeakFastHashMap<K,V> extends HashMap<K,V>
A customized implementation of java.util.HashMap designed
to operate in a multithreaded environment where the large majority of
method calls are read-only, instead of structural changes. When operating
in "fast" mode, read calls are non-synchronized and write calls perform the
following steps:
When first created, objects of this class default to "slow" mode, where
all accesses of any type are synchronized but no cloning takes place. This
is appropriate for initially populating the collection, followed by a switch
to "fast" mode (by calling setFast(true)) after initialization
is complete.
NOTE: If you are creating and accessing a
HashMap only within a single thread, you should use
java.util.HashMap directly (with no synchronization), for
maximum performance.
NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declaration.
AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>| Constructor and Description |
|---|
WeakFastHashMap()
Construct an empty map.
|
WeakFastHashMap(int capacity)
Construct an empty map with the specified capacity.
|
WeakFastHashMap(int capacity,
float factor)
Construct an empty map with the specified capacity and load factor.
|
WeakFastHashMap(Map<? extends K,? extends V> map)
Construct a new map with the same mappings as the specified map.
|
| Modifier and Type | Method and Description |
|---|---|
void |
clear()
Remove all mappings from this map.
|
Object |
clone()
Return a shallow copy of this
FastHashMap instance. |
protected Map<K,V> |
cloneMap(Map<? extends K,? extends V> map) |
boolean |
containsKey(Object key)
Return
true if this map contains a mapping for the
specified key. |
boolean |
containsValue(Object value)
Return
true if this map contains one or more keys mapping
to the specified value. |
protected Map<K,V> |
createMap() |
protected Map<K,V> |
createMap(int capacity) |
protected Map<K,V> |
createMap(int capacity,
float factor) |
protected Map<K,V> |
createMap(Map<? extends K,? extends V> map) |
Set<Map.Entry<K,V>> |
entrySet()
Return a collection view of the mappings contained in this map.
|
boolean |
equals(Object o)
Compare the specified object with this list for equality.
|
V |
get(Object key)
Return the value to which this map maps the specified key.
|
boolean |
getFast()
Returns true if this map is operating in fast mode.
|
int |
hashCode()
Return the hash code value for this map.
|
boolean |
isEmpty()
Return
true if this map contains no mappings. |
Set<K> |
keySet()
Return a set view of the keys contained in this map.
|
V |
put(K key,
V value)
Associate the specified value with the specified key in this map.
|
void |
putAll(Map<? extends K,? extends V> in)
Copy all of the mappings from the specified map to this one, replacing
any mappings with the same keys.
|
V |
remove(Object key)
Remove any mapping for this key, and return any previously
mapped value.
|
void |
setFast(boolean fast)
Sets whether this map is operating in fast mode.
|
int |
size()
Return the number of key-value mappings in this map.
|
Collection<V> |
values()
Return a collection view of the values contained in this map.
|
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAlltoStringpublic WeakFastHashMap()
public WeakFastHashMap(int capacity)
capacity - the initial capacity of the empty mappublic WeakFastHashMap(int capacity,
float factor)
capacity - the initial capacity of the empty mapfactor - the load factor of the new mappublic boolean getFast()
public void setFast(boolean fast)
fast - true if this map should operate in fast modepublic V get(Object key)
null if the map contains no mapping for this key, or if
there is a mapping with a value of null. Use the
containsKey() method to disambiguate these cases.public int size()
public boolean isEmpty()
true if this map contains no mappings.public boolean containsKey(Object key)
true if this map contains a mapping for the
specified key.containsKey in interface Map<K,V>containsKey in class HashMap<K,V>key - the key to be searched forpublic boolean containsValue(Object value)
true if this map contains one or more keys mapping
to the specified value.containsValue in interface Map<K,V>containsValue in class HashMap<K,V>value - the value to be searched forpublic V put(K key, V value)
public void putAll(Map<? extends K,? extends V> in)
public V remove(Object key)
public void clear()
public boolean equals(Object o)
Map.equals method.public int hashCode()
Map.hashCode method.public Object clone()
FastHashMap instance.
The keys and values themselves are not copied.public Set<Map.Entry<K,V>> entrySet()
Map.Entry.public Collection<V> values()
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