Class WeakFastHashMap<K,V>
- java.lang.Object
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- java.util.AbstractMap<K,V>
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- java.util.HashMap<K,V>
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- org.apache.commons.beanutils.WeakFastHashMap<K,V>
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- All Implemented Interfaces:
java.io.Serializable
,java.lang.Cloneable
,java.util.Map<K,V>
class WeakFastHashMap<K,V> extends java.util.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:- Clone the existing collection
- Perform the modification on the clone
- Replace the existing collection with the (modified) clone
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 usejava.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.
- Since:
- Commons Collections 1.0
- Version:
- $Id$
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Nested Class Summary
Nested Classes Modifier and Type Class Description private class
WeakFastHashMap.CollectionView<E>
Abstract collection implementation shared by keySet(), values() and entrySet().private class
WeakFastHashMap.EntrySet
Set implementation over the entries of the FastHashMapprivate class
WeakFastHashMap.KeySet
Set implementation over the keys of the FastHashMapprivate class
WeakFastHashMap.Values
Collection implementation over the values of the FastHashMap
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Constructor Summary
Constructors Constructor 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(java.util.Map<? extends K,? extends V> map)
Construct a new map with the same mappings as the specified map.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
clear()
Remove all mappings from this map.java.lang.Object
clone()
Return a shallow copy of thisFastHashMap
instance.protected java.util.Map<K,V>
cloneMap(java.util.Map<? extends K,? extends V> map)
boolean
containsKey(java.lang.Object key)
Returntrue
if this map contains a mapping for the specified key.boolean
containsValue(java.lang.Object value)
Returntrue
if this map contains one or more keys mapping to the specified value.protected java.util.Map<K,V>
createMap()
protected java.util.Map<K,V>
createMap(int capacity)
protected java.util.Map<K,V>
createMap(int capacity, float factor)
protected java.util.Map<K,V>
createMap(java.util.Map<? extends K,? extends V> map)
java.util.Set<java.util.Map.Entry<K,V>>
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.V
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()
Returntrue
if this map contains no mappings.java.util.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(java.util.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(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<V>
values()
Return a collection view of the values contained in this map.
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Constructor Detail
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WeakFastHashMap
public WeakFastHashMap()
Construct an empty map.
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WeakFastHashMap
public WeakFastHashMap(int capacity)
Construct an empty map with the specified capacity.- Parameters:
capacity
- the initial capacity of the empty map
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WeakFastHashMap
public WeakFastHashMap(int capacity, float factor)
Construct an empty map with the specified capacity and load factor.- Parameters:
capacity
- the initial capacity of the empty mapfactor
- the load factor of the new map
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Method Detail
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getFast
public boolean getFast()
Returns true if this map is operating in fast mode.- Returns:
- true if this map is operating in fast mode
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setFast
public void setFast(boolean fast)
Sets whether this map is operating in fast mode.- Parameters:
fast
- true if this map should operate in fast mode
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get
public V get(java.lang.Object key)
Return the value to which this map maps the specified key. Returnsnull
if the map contains no mapping for this key, or if there is a mapping with a value ofnull
. Use thecontainsKey()
method to disambiguate these cases.
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size
public int size()
Return the number of key-value mappings in this map.
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isEmpty
public boolean isEmpty()
Returntrue
if this map contains no mappings.
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containsKey
public boolean containsKey(java.lang.Object key)
Returntrue
if this map contains a mapping for the specified key.
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containsValue
public boolean containsValue(java.lang.Object value)
Returntrue
if this map contains one or more keys mapping to the specified value.
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put
public V put(K key, V value)
Associate 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 and returned.
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putAll
public void putAll(java.util.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.
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remove
public V remove(java.lang.Object key)
Remove any mapping for this key, and return any previously mapped value.
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clear
public void clear()
Remove all mappings from this map.
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equals
public boolean equals(java.lang.Object o)
Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for theMap.equals
method.
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hashCode
public int hashCode()
Return the hash code value for this map. This implementation uses exactly the code that is used to define the list hash function in the documentation for theMap.hashCode
method.
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clone
public java.lang.Object clone()
Return a shallow copy of thisFastHashMap
instance. The keys and values themselves are not copied.
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entrySet
public java.util.Set<java.util.Map.Entry<K,V>> entrySet()
Return a collection view of the mappings contained in this map. Each element in the returned collection is aMap.Entry
.
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keySet
public java.util.Set<K> keySet()
Return a set view of the keys contained in this map.
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values
public java.util.Collection<V> values()
Return a collection view of the values contained in this map.
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