public class FastHashMap
extends java.util.HashMap
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.
Constructor and Description |
---|
FastHashMap()
Construct an empty map.
|
FastHashMap(int capacity)
Construct an empty map with the specified capacity.
|
FastHashMap(int capacity,
float factor)
Construct an empty map with the specified capacity and load factor.
|
FastHashMap(java.util.Map 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.
|
java.lang.Object |
clone()
Return a shallow copy of this
FastHashMap instance. |
boolean |
containsKey(java.lang.Object key)
Return
true if this map contains a mapping for the
specified key. |
boolean |
containsValue(java.lang.Object value)
Return
true if this map contains one or more keys mapping
to the specified value. |
java.util.Set |
entrySet()
Return a collection view of the mappings contained in this map.
|
boolean |
equals(java.lang.Object o)
Compare the specified object with this list for equality.
|
java.lang.Object |
get(java.lang.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. |
java.util.Set |
keySet()
Return a set view of the keys contained in this map.
|
java.lang.Object |
put(java.lang.Object key,
java.lang.Object value)
Associate the specified value with the specified key in this map.
|
void |
putAll(java.util.Map in)
Copy all of the mappings from the specified map to this one, replacing
any mappings with the same keys.
|
java.lang.Object |
remove(java.lang.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.
|
java.util.Collection |
values()
Return a collection view of the values contained in this map.
|
public FastHashMap()
public FastHashMap(int capacity)
capacity
- the initial capacity of the empty mappublic FastHashMap(int capacity, float factor)
capacity
- the initial capacity of the empty mapfactor
- the load factor of the new mappublic FastHashMap(java.util.Map map)
map
- the map whose mappings are to be copiedpublic boolean getFast()
public void setFast(boolean fast)
fast
- true if this map should operate in fast modepublic java.lang.Object get(java.lang.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.get
in interface java.util.Map
get
in class java.util.HashMap
key
- the key whose value is to be returnedpublic int size()
size
in interface java.util.Map
size
in class java.util.HashMap
public boolean isEmpty()
true
if this map contains no mappings.isEmpty
in interface java.util.Map
isEmpty
in class java.util.HashMap
public boolean containsKey(java.lang.Object key)
true
if this map contains a mapping for the
specified key.containsKey
in interface java.util.Map
containsKey
in class java.util.HashMap
key
- the key to be searched forpublic boolean containsValue(java.lang.Object value)
true
if this map contains one or more keys mapping
to the specified value.containsValue
in interface java.util.Map
containsValue
in class java.util.HashMap
value
- the value to be searched forpublic java.lang.Object put(java.lang.Object key, java.lang.Object value)
put
in interface java.util.Map
put
in class java.util.HashMap
key
- the key with which the value is to be associatedvalue
- the value to be associated with this keypublic void putAll(java.util.Map in)
putAll
in interface java.util.Map
putAll
in class java.util.HashMap
in
- the map whose mappings are to be copiedpublic java.lang.Object remove(java.lang.Object key)
remove
in interface java.util.Map
remove
in class java.util.HashMap
key
- the key whose mapping is to be removedpublic void clear()
clear
in interface java.util.Map
clear
in class java.util.HashMap
public boolean equals(java.lang.Object o)
Map.equals
method.equals
in interface java.util.Map
equals
in class java.util.AbstractMap
o
- the object to be compared to this listpublic int hashCode()
Map.hashCode
method.hashCode
in interface java.util.Map
hashCode
in class java.util.AbstractMap
public java.lang.Object clone()
FastHashMap
instance.
The keys and values themselves are not copied.clone
in class java.util.HashMap
public java.util.Set entrySet()
Map.Entry
.entrySet
in interface java.util.Map
entrySet
in class java.util.HashMap
public java.util.Set keySet()
keySet
in interface java.util.Map
keySet
in class java.util.HashMap
public java.util.Collection values()
values
in interface java.util.Map
values
in class java.util.HashMap
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