FastHashMap (Apache Commons Collections 3.2.2 API)

java.lang.Object
- java.util.AbstractMap
- - java.util.HashMap
  - - org.apache.commons.collections.FastHashMap

All Implemented Interfaces:

Serializable, Cloneable, Map
```
public class FastHashMap
extends 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:
- 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 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.
Since:

Commons Collections 1.0

Version:

$Revision: 972404 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $

Author:

Craig R. McClanahan, Stephen Colebourne

See Also:
Serialized Form

Nested Class Summary
- Nested classes/interfaces inherited from class java.util.AbstractMap
  AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry

Field Summary

Fields
Modifier and Type Field and Description

protected boolean fast
Are we currently operating in "fast" mode?

protected HashMap map
The underlying map we are managing.

Fields
Modifier and Type	Field and Description
`protected boolean`	`fast` Are we currently operating in "fast" mode?
`protected HashMap`	`map` The underlying map we are managing.

Constructor Summary

Constructors
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(Map map)` Construct a new map with the same mappings as the specified map.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`clear()` Remove all mappings from this map.
`Object`	`clone()` Return a shallow copy of this `FastHashMap` instance.
`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.
`Set`	`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.
`Object`	`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`	`keySet()` Return a set view of the keys contained in this map.
`Object`	`put(Object key, Object value)` Associate the specified value with the specified key in this map.
`void`	`putAll(Map in)` Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.
`Object`	`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`	`values()` Return a collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap
toString

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - map
```
protected HashMap map
```
    The underlying map we are managing.
  - fast
```
protected boolean fast
```
    Are we currently operating in "fast" mode?
- Constructor Detail
  - FastHashMap
```
public FastHashMap()
```
    Construct an empty map.
  - FastHashMap
```
public FastHashMap(int capacity)
```
    Construct an empty map with the specified capacity.
    
    Parameters:
    capacity - the initial capacity of the empty map
  - FastHashMap
```
public FastHashMap(int capacity,
           float factor)
```
    Construct an empty map with the specified capacity and load factor.
    
    Parameters:
    capacity - the initial capacity of the empty map
    factor - the load factor of the new map
  - FastHashMap
```
public FastHashMap(Map map)
```
    Construct a new map with the same mappings as the specified map.
    
    Parameters:
    map - the map whose mappings are to be copied
- Method Detail
  - getFast
```
public boolean getFast()
```
    Returns true if this map is operating in fast mode.
    
    Returns:
    true if this map is operating in fast mode
  - 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
  - get
```
public Object get(Object key)
```
    Return the value to which this map maps the specified key. Returns 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.
    
    Specified by:
    
    get in interface Map
    
    Overrides:
    
    get in class HashMap
    
    Parameters:
    key - the key whose value is to be returned
    
    Returns:
    the value mapped to that key, or null
  - size
```
public int size()
```
    Return the number of key-value mappings in this map.
    
    Specified by:
    
    size in interface Map
    
    Overrides:
    
    size in class HashMap
    
    Returns:
    the current size of the map
  - isEmpty
```
public boolean isEmpty()
```
    Return true if this map contains no mappings.
    
    Specified by:
    
    isEmpty in interface Map
    
    Overrides:
    
    isEmpty in class HashMap
    
    Returns:
    is the map currently empty
  - containsKey
```
public boolean containsKey(Object key)
```
    Return true if this map contains a mapping for the specified key.
    
    Specified by:
    
    containsKey in interface Map
    
    Overrides:
    
    containsKey in class HashMap
    
    Parameters:
    key - the key to be searched for
    
    Returns:
    true if the map contains the key
  - containsValue
```
public boolean containsValue(Object value)
```
    Return true if this map contains one or more keys mapping to the specified value.
    
    Specified by:
    
    containsValue in interface Map
    
    Overrides:
    
    containsValue in class HashMap
    
    Parameters:
    value - the value to be searched for
    
    Returns:
    true if the map contains the value
  - put
```
public Object put(Object key,
         Object 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.
    
    Specified by:
    
    put in interface Map
    
    Overrides:
    
    put in class HashMap
    
    Parameters:
    key - the key with which the value is to be associated
    value - the value to be associated with this key
    
    Returns:
    the value previously mapped to the key, or null
  - putAll
```
public void putAll(Map in)
```
    Copy all of the mappings from the specified map to this one, replacing any mappings with the same keys.
    
    Specified by:
    
    putAll in interface Map
    
    Overrides:
    
    putAll in class HashMap
    
    Parameters:
    in - the map whose mappings are to be copied
  - remove
```
public Object remove(Object key)
```
    Remove any mapping for this key, and return any previously mapped value.
    
    Specified by:
    
    remove in interface Map
    
    Overrides:
    
    remove in class HashMap
    
    Parameters:
    key - the key whose mapping is to be removed
    
    Returns:
    the value removed, or null
  - clear
```
public void clear()
```
    Remove all mappings from this map.
    
    Specified by:
    
    clear in interface Map
    
    Overrides:
    
    clear in class HashMap
  - equals
```
public boolean equals(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 the Map.equals method.
    
    Specified by:
    
    equals in interface Map
    
    Overrides:
    
    equals in class AbstractMap
    
    Parameters:
    o - the object to be compared to this list
    
    Returns:
    true if the two maps are equal
  - 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 the Map.hashCode method.
    
    Specified by:
    
    hashCode in interface Map
    
    Overrides:
    
    hashCode in class AbstractMap
    
    Returns:
    suitable integer hash code
  - clone
```
public Object clone()
```
    Return a shallow copy of this FastHashMap instance. The keys and values themselves are not copied.
    
    Overrides:
    
    clone in class HashMap
    
    Returns:
    a clone of this map
  - entrySet
```
public Set entrySet()
```
    Return a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry.
    
    Specified by:
    
    entrySet in interface Map
    
    Overrides:
    
    entrySet in class HashMap
  - keySet
```
public Set keySet()
```
    Return a set view of the keys contained in this map.
    
    Specified by:
    
    keySet in interface Map
    
    Overrides:
    
    keySet in class HashMap
  - values
```
public Collection values()
```
    Return a collection view of the values contained in this map.
    
    Specified by:
    
    values in interface Map
    
    Overrides:
    
    values in class HashMap

Class FastHashMap

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractMap

Methods inherited from class java.lang.Object

Field Detail

map

fast

Constructor Detail

FastHashMap

FastHashMap

FastHashMap

FastHashMap

Method Detail

getFast

setFast

get

size

isEmpty

containsKey

containsValue

put

putAll

remove

clear

equals

hashCode

clone

entrySet

keySet

values