Class Flat3Map<K,V>
- Type Parameters:
K
- the type of the keys in this mapV
- 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>
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:
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Nested Class Summary
Nested ClassesModifier and TypeClassDescription(package private) static class
(package private) static class
EntrySet(package private) static class
EntrySetIterator and MapEntry(package private) static class
(package private) static class
FlatMapIterator(package private) static class
KeySet(package private) static class
KeySetIterator(package private) static class
Values(package private) static class
ValuesIterator -
Field Summary
FieldsModifier and TypeFieldDescriptionprivate AbstractHashedMap
<K, V> Map, used while in delegate modeprivate int
Hash, used while in flat modeprivate int
Hash, used while in flat modeprivate int
Hash, used while in flat modeprivate K
Key, used while in flat modeprivate K
Key, used while in flat modeprivate K
Key, used while in flat modeprivate static final long
Serialization versionprivate int
The size of the map, used while in flat modeprivate V
Value, used while in flat modeprivate V
Value, used while in flat modeprivate V
Value, used while in flat mode -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.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.private void
Converts the flat map data to a map.protected AbstractHashedMap
<K, V> Create an instance of the map used for storage when in delegation mode.entrySet()
Gets the entrySet view of the map.boolean
Compares this map with another.Gets the value mapped to the key specified.int
hashCode()
Gets the standard Map hashCode.boolean
isEmpty()
Checks whether the map is currently empty.keySet()
Gets the keySet view of the map.Gets an iterator over the map.Puts a key-value mapping into this map.void
Puts all the values from the specified map into this map.private void
Read the map in using a custom routine.Removes the specified mapping from this map.int
size()
Gets the size of the map.toString()
Gets the map as a String.values()
Gets the values view of the map.private void
Write the map out using a custom routine.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
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Field Details
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serialVersionUID
private static final long serialVersionUIDSerialization version- See Also:
-
size
private transient int sizeThe size of the map, used while in flat mode -
hash1
private transient int hash1Hash, used while in flat mode -
hash2
private transient int hash2Hash, used while in flat mode -
hash3
private transient int hash3Hash, used while in flat mode -
key1
Key, used while in flat mode -
key2
Key, used while in flat mode -
key3
Key, used while in flat mode -
value1
Value, used while in flat mode -
value2
Value, used while in flat mode -
value3
Value, used while in flat mode -
delegateMap
Map, used while in delegate mode
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Constructor Details
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Flat3Map
public Flat3Map()Constructor. -
Flat3Map
Constructor copying elements from another map.- Parameters:
map
- the map to copy- Throws:
NullPointerException
- if the map is null
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Method Details
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get
Gets the value mapped to the key specified. -
size
public int size()Gets the size of the map. -
isEmpty
public boolean isEmpty()Checks whether the map is currently empty. -
containsKey
Checks whether the map contains the specified key.- Specified by:
containsKey
in interfaceGet<K,
V> - Specified by:
containsKey
in interfaceMap<K,
V> - Parameters:
key
- the key to search for- Returns:
- true if the map contains the key
- See Also:
-
containsValue
Checks whether the map contains the specified value.- Specified by:
containsValue
in interfaceGet<K,
V> - Specified by:
containsValue
in interfaceMap<K,
V> - Parameters:
value
- the value to search for- Returns:
- true if the map contains the key
- See Also:
-
put
Puts a key-value mapping into this map. -
putAll
Puts all the values from the specified map into this map. -
convertToMap
private void convertToMap()Converts the flat map data to a map. -
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
Removes the specified mapping from this map. -
clear
public void clear()Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues. -
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 interfaceIterableGet<K,
V> - Returns:
- the map iterator
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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()
. -
keySet
Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, usemapIterator()
. -
values
Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, usemapIterator()
. -
writeObject
Write the map out using a custom routine.- Parameters:
out
- the output stream- Throws:
IOException
- if an error occurs while writing to the stream
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readObject
Read the map in using a custom routine.- Parameters:
in
- the input stream- Throws:
IOException
- if an error occurs while reading from the streamClassNotFoundException
- if an object read from the stream can not be loaded
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clone
Clones the map without cloning the keys or values. -
equals
Compares this map with another. -
hashCode
public int hashCode()Gets the standard Map hashCode. -
toString
Gets the map as a String.
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