org.apache.commons.collections.map

Class LRUMap

java.lang.Object

java.util.AbstractMap

org.apache.commons.collections.map.AbstractHashedMap

org.apache.commons.collections.map.AbstractLinkedMap

org.apache.commons.collections.map.LRUMap

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map, BoundedMap, IterableMap, OrderedMap

public class LRUMap
extends AbstractLinkedMap
implements BoundedMap, java.io.Serializable, java.lang.Cloneable

A Map implementation with a fixed maximum size which removes the least recently used entry if an entry is added when full.

The least recently used algorithm works on the get and put operations only. Iteration of any kind, including setting the value by iteration, does not change the order. Queries such as containsKey and containsValue or access via views also do not change the order.

The map implements OrderedMap and entries may be queried using the bidirectional OrderedMapIterator. The order returned is least recently used to most recently used. Iterators from map views can also be cast to OrderedIterator if required.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

Note that LRUMap 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 NullPointerException's when accessed by concurrent threads.

Since:

Commons Collections 3.0 (previously in main package v1.0)

See Also:

Serialized Form

Nested Class Summary

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

java.util.AbstractMap.SimpleEntry<K,V>, java.util.AbstractMap.SimpleImmutableEntry<K,V>

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

java.util.Map.Entry<K,V>

Constructor Summary

Constructors

Constructor and Description
LRUMap() Constructs a new empty map with a maximum size of 100.
LRUMap(int maxSize) Constructs a new, empty map with the specified maximum size.
LRUMap(int maxSize, boolean scanUntilRemovable) Constructs a new, empty map with the specified maximum size.
LRUMap(int maxSize, float loadFactor) Constructs a new, empty map with the specified initial capacity and load factor.
LRUMap(int maxSize, float loadFactor, boolean scanUntilRemovable) Constructs a new, empty map with the specified initial capacity and load factor.
LRUMap(java.util.Map map) Constructor copying elements from another map.
LRUMap(java.util.Map map, boolean scanUntilRemovable) Constructor copying elements from another map.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	clone() Clones the map without cloning the keys or values.
java.lang.Object	get(java.lang.Object key) Gets the value mapped to the key specified.
boolean	isFull() Returns true if this map is full and no new mappings can be added.
boolean	isScanUntilRemovable() Whether this LRUMap will scan until a removable entry is found when the map is full.
int	maxSize() Gets the maximum size of the map (the bound).

Methods inherited from class org.apache.commons.collections.map.AbstractLinkedMap

clear, containsValue, firstKey, lastKey, mapIterator, nextKey, orderedMapIterator, previousKey

Methods inherited from class org.apache.commons.collections.map.AbstractHashedMap

containsKey, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values

Constructor Detail

LRUMap

public LRUMap()

Constructs a new empty map with a maximum size of 100.

LRUMap

public LRUMap(int maxSize)

Constructs a new, empty map with the specified maximum size.

Parameters:

maxSize - the maximum size of the map

Throws:

java.lang.IllegalArgumentException - if the maximum size is less than one

LRUMap

public LRUMap(int maxSize,
              boolean scanUntilRemovable)

Constructs a new, empty map with the specified maximum size.

Parameters:

maxSize - the maximum size of the map

scanUntilRemovable - scan until a removeable entry is found, default false

Throws:

java.lang.IllegalArgumentException - if the maximum size is less than one

Since:

Commons Collections 3.1

LRUMap

public LRUMap(int maxSize,
              float loadFactor)

Constructs a new, empty map with the specified initial capacity and load factor.

Parameters:

maxSize - the maximum size of the map, -1 for no limit,

loadFactor - the load factor

Throws:

java.lang.IllegalArgumentException - if the maximum size is less than one

java.lang.IllegalArgumentException - if the load factor is less than zero

LRUMap

public LRUMap(int maxSize,
              float loadFactor,
              boolean scanUntilRemovable)

Constructs a new, empty map with the specified initial capacity and load factor.

Parameters:

maxSize - the maximum size of the map, -1 for no limit,

loadFactor - the load factor

scanUntilRemovable - scan until a removeable entry is found, default false

Throws:

java.lang.IllegalArgumentException - if the maximum size is less than one

java.lang.IllegalArgumentException - if the load factor is less than zero

Since:

Commons Collections 3.1

LRUMap

public LRUMap(java.util.Map map)

Constructor copying elements from another map.

The maximum size is set from the map's size.

Parameters:

map - the map to copy

Throws:

java.lang.NullPointerException - if the map is null

java.lang.IllegalArgumentException - if the map is empty

LRUMap

public LRUMap(java.util.Map map,
              boolean scanUntilRemovable)

Constructor copying elements from another map.

The maximum size is set from the map's size.

Parameters:

map - the map to copy

scanUntilRemovable - scan until a removeable entry is found, default false

Throws:

java.lang.NullPointerException - if the map is null

java.lang.IllegalArgumentException - if the map is empty

Since:

Commons Collections 3.1

Method Detail

get

public java.lang.Object get(java.lang.Object key)

Gets the value mapped to the key specified.

This operation changes the position of the key in the map to the most recently used position (first).

Specified by:

get in interface java.util.Map

Overrides:

get in class AbstractHashedMap

Parameters:

key - the key

Returns:

the mapped value, null if no match

isFull

public boolean isFull()

Returns true if this map is full and no new mappings can be added.

Specified by:

isFull in interface BoundedMap

Returns:

true if the map is full

maxSize

public int maxSize()

Gets the maximum size of the map (the bound).

Specified by:

maxSize in interface BoundedMap

Returns:

the maximum number of elements the map can hold

isScanUntilRemovable

public boolean isScanUntilRemovable()

Whether this LRUMap will scan until a removable entry is found when the map is full.

Returns:

true if this map scans

Since:

Commons Collections 3.1

clone

public java.lang.Object clone()

Clones the map without cloning the keys or values.

Returns:

a shallow clone