Flat3Map (Apache Commons Collections 4.4 API)

java.lang.Object
- org.apache.commons.collections4.map.Flat3Map<K,V>

Type Parameters:

K - the type of the keys in this map

V - the type of the values in this map

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>
```
public class Flat3Map<K,V>
extends Object
implements IterableMap<K,V>, Serializable, Cloneable
```
A Map implementation that stores data in simple fields until the size is greater than 3.
This map is designed for performance and can outstrip HashMap. It also has good garbage collection characteristics.
- Optimised for operation at size 3 or less.
- Still works well once size 3 exceeded.
- Gets at size 3 or less are about 0-10% faster than HashMap,
- Puts at size 3 or less are over 4 times faster than HashMap.
- Performance 5% slower than HashMap once size 3 exceeded once.
The design uses two distinct modes of operation - flat and delegate. While the map is size 3 or less, operations map straight onto fields using switch statements. Once size 4 is reached, the map switches to delegate mode and only switches back when cleared. In delegate mode, all operations are forwarded straight to a HashMap resulting in the 5% performance loss.

The performance gains on puts are due to not needing to create a Map Entry object. This is a large saving not only in performance but in garbage collection.

Whilst in flat mode this map is also easy for the garbage collector to dispatch. This is because it contains no complex objects or arrays which slow the progress.

Do not use Flat3Map if the size is likely to grow beyond 3.

Note that Flat3Map is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.
Since:

3.0

See Also:

Serialized Form

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  Map.Entry<K,V>

Constructor Summary

Constructors
Constructor and Description

Flat3Map()
Constructor.

Flat3Map(Map<? extends K,? extends V> map)
Constructor copying elements from another map.

Constructors
Constructor and Description
`Flat3Map()` Constructor.
`Flat3Map(Map<? extends K,? extends V> map)` Constructor copying elements from another map.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`clear()` Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
`Flat3Map<K,V>`	`clone()` Clones the map without cloning the keys or values.
`boolean`	`containsKey(Object key)` Checks whether the map contains the specified key.
`boolean`	`containsValue(Object value)` Checks whether the map contains the specified value.
`protected AbstractHashedMap<K,V>`	`createDelegateMap()` Create an instance of the map used for storage when in delegation mode.
`Set<Map.Entry<K,V>>`	`entrySet()` Gets the entrySet view of the map.
`boolean`	`equals(Object obj)` Compares this map with another.
`V`	`get(Object key)` Gets the value mapped to the key specified.
`int`	`hashCode()` Gets the standard Map hashCode.
`boolean`	`isEmpty()` Checks whether the map is currently empty.
`Set<K>`	`keySet()` Gets the keySet view of the map.
`MapIterator<K,V>`	`mapIterator()` Gets an iterator over the map.
`V`	`put(K key, V value)` Puts a key-value mapping into this map.
`void`	`putAll(Map<? extends K,? extends V> map)` Puts all the values from the specified map into this map.
`V`	`remove(Object key)` Removes the specified mapping from this map.
`int`	`size()` Gets the size of the map.
`String`	`toString()` Gets the map as a String.
`Collection<V>`	`values()` Gets the values view of the map.

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

Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

- Constructor Detail
  - Flat3Map
```
public Flat3Map()
```
    Constructor.
  - Flat3Map
```
public Flat3Map(Map<? extends K,? extends V> map)
```
    Constructor copying elements from another map.
    
    Parameters:
    
    map - the map to copy
    
    Throws:
    
    NullPointerException - if the map is null
- Method Detail
  - get
```
public V get(Object key)
```
    Gets the value mapped to the key specified.
    
    Specified by:
    
    get in interface Map<K,V>
    
    Specified by:
    
    get in interface Get<K,V>
    
    Parameters:
    
    key - the key
    
    Returns:
    
    the mapped value, null if no match
    
    See Also:
    
    Map.get(Object)
  - size
```
public int size()
```
    Gets the size of the map.
    
    Specified by:
    
    size in interface Map<K,V>
    
    Specified by:
    
    size in interface Get<K,V>
    
    Returns:
    
    the size
    
    See Also:
    
    Map.size()
  - isEmpty
```
public boolean isEmpty()
```
    Checks whether the map is currently empty.
    
    Specified by:
    
    isEmpty in interface Map<K,V>
    
    Specified by:
    
    isEmpty in interface Get<K,V>
    
    Returns:
    
    true if the map is currently size zero
    
    See Also:
    
    Map.isEmpty()
  - containsKey
```
public boolean containsKey(Object key)
```
    Checks whether the map contains the specified key.
    
    Specified by:
    
    containsKey in interface Map<K,V>
    
    Specified by:
    
    containsKey in interface Get<K,V>
    
    Parameters:
    
    key - the key to search for
    
    Returns:
    
    true if the map contains the key
    
    See Also:
    
    Map.containsKey(Object)
  - containsValue
```
public boolean containsValue(Object value)
```
    Checks whether the map contains the specified value.
    
    Specified by:
    
    containsValue in interface Map<K,V>
    
    Specified by:
    
    containsValue in interface Get<K,V>
    
    Parameters:
    
    value - the value to search for
    
    Returns:
    
    true if the map contains the key
    
    See Also:
    
    Map.containsValue(Object)
  - put
```
public V put(K key,
             V value)
```
    Puts a key-value mapping into this map.
    
    Specified by:
    
    put in interface Map<K,V>
    
    Specified by:
    
    put in interface Put<K,V>
    
    Parameters:
    
    key - the key to add
    
    value - the value to add
    
    Returns:
    
    the value previously mapped to this key, null if none
    
    See Also:
    
    Map.put(Object, Object)
  - putAll
```
public void putAll(Map<? extends K,? extends V> map)
```
    Puts all the values from the specified map into this map.
    
    Specified by:
    
    putAll in interface Map<K,V>
    
    Specified by:
    
    putAll in interface Put<K,V>
    
    Parameters:
    
    map - the map to add
    
    Throws:
    
    NullPointerException - if the map is null
    
    See Also:
    
    Map.putAll(Map)
  - createDelegateMap
```
protected AbstractHashedMap<K,V> createDelegateMap()
```
    Create an instance of the map used for storage when in delegation mode.
    This can be overridden by subclasses to provide a different map implementation. Not every AbstractHashedMap is suitable, identity and reference based maps would be poor choices.
    
    Returns:
    
    a new AbstractHashedMap or subclass
    
    Since:
    
    3.1
  - remove
```
public V remove(Object key)
```
    Removes the specified mapping from this map.
    
    Specified by:
    
    remove in interface Map<K,V>
    
    Specified by:
    
    remove in interface Get<K,V>
    
    Parameters:
    
    key - the mapping to remove
    
    Returns:
    
    the value mapped to the removed key, null if key not in map
    
    See Also:
    
    Map.remove(Object)
  - clear
```
public void clear()
```
    Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
    
    Specified by:
    
    clear in interface Map<K,V>
    
    Specified by:
    
    clear in interface Put<K,V>
    
    See Also:
    
    Map.clear()
  - mapIterator
```
public MapIterator<K,V> mapIterator()
```
    Gets an iterator over the map. Changes made to the iterator affect this map.
    A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map Entry object.
    
    Specified by:
    
    mapIterator in interface IterableGet<K,V>
    
    Returns:
    
    the map iterator
  - entrySet
```
public Set<Map.Entry<K,V>> entrySet()
```
    Gets the entrySet view of the map. Changes made to the view affect this map.
    NOTE: from 4.0, the returned Map Entry will be an independent object and will not change anymore as the iterator progresses. To avoid this additional object creation and simply iterate through the entries, use mapIterator().
    
    Specified by:
    
    entrySet in interface Map<K,V>
    
    Specified by:
    
    entrySet in interface Get<K,V>
    
    Returns:
    
    the entrySet view
    
    See Also:
    
    Map.entrySet()
  - keySet
```
public Set<K> keySet()
```
    Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator().
    
    Specified by:
    
    keySet in interface Map<K,V>
    
    Specified by:
    
    keySet in interface Get<K,V>
    
    Returns:
    
    the keySet view
    
    See Also:
    
    Map.keySet()
  - values
```
public Collection<V> values()
```
    Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, use mapIterator().
    
    Specified by:
    
    values in interface Map<K,V>
    
    Specified by:
    
    values in interface Get<K,V>
    
    Returns:
    
    the values view
    
    See Also:
    
    Map.values()
  - clone
```
public Flat3Map<K,V> clone()
```
    Clones the map without cloning the keys or values.
    
    Overrides:
    
    clone in class Object
    
    Returns:
    
    a shallow clone
    
    Since:
    
    3.1
  - equals
```
public boolean equals(Object obj)
```
    Compares this map with another.
    
    Specified by:
    
    equals in interface Map<K,V>
    
    Overrides:
    
    equals in class Object
    
    Parameters:
    
    obj - the object to compare to
    
    Returns:
    
    true if equal
  - hashCode
```
public int hashCode()
```
    Gets the standard Map hashCode.
    
    Specified by:
    
    hashCode in interface Map<K,V>
    
    Overrides:
    
    hashCode in class Object
    
    Returns:
    
    the hash code defined in the Map interface
  - toString
```
public String toString()
```
    Gets the map as a String.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    
    a string version of the map

Class Flat3Map<K,V>

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Constructor Detail

Flat3Map

Flat3Map

Method Detail

get

size

isEmpty

containsKey

containsValue

put

putAll

createDelegateMap

remove

clear

mapIterator

entrySet

keySet

values

clone

equals

hashCode

toString