public class LRUMap extends SequencedHashMap implements Externalizable
An implementation of a Map which has a maximum size and uses a Least Recently Used algorithm to remove items from the Map when the maximum size is reached and new items are added.
A synchronized version can be obtained with:
Collections.synchronizedMap( theMapToSynchronize )
If it will be accessed by multiple threads, you _must_ synchronize access
to this Map. Even concurrent get(Object) operations produce indeterminate
behaviour.
Unlike the Collections 1.0 version, this version of LRUMap does use a true LRU algorithm. The keys for all gets and puts are moved to the front of the list. LRUMap is now a subclass of SequencedHashMap, and the "LRU" key is now equivalent to LRUMap.getFirst().
| Constructor and Description |
|---|
LRUMap()
Default constructor, primarily for the purpose of
de-externalization.
|
LRUMap(int i)
Create a new LRUMap with a maximum capacity of i.
|
| Modifier and Type | Method and Description |
|---|---|
Object |
get(Object key)
Get the value for a key from the Map.
|
int |
getMaximumSize()
Getter for property maximumSize.
|
protected void |
processRemovedLRU(Object key,
Object value)
Subclasses of LRUMap may hook into this method to
provide specialized actions whenever an Object is
automatically removed from the cache.
|
Object |
put(Object key,
Object value)
Removes the key and its Object from the Map.
|
void |
readExternal(ObjectInput in)
Deserializes this map from the given stream.
|
protected void |
removeLRU()
This method is used internally by the class for
finding and removing the LRU Object.
|
void |
setMaximumSize(int maximumSize)
Setter for property maximumSize.
|
void |
writeExternal(ObjectOutput out)
Serializes this map to the given stream.
|
clear, clone, containsKey, containsValue, entrySet, equals, get, getFirst, getFirstKey, getFirstValue, getLast, getLastKey, getLastValue, getValue, hashCode, indexOf, isEmpty, iterator, keySet, lastIndexOf, putAll, remove, remove, sequence, size, toString, valuespublic LRUMap()
public LRUMap(int i)
i - Maximum capacity of the LRUMappublic Object get(Object key)
Get the value for a key from the Map. The key will be promoted to the Most Recently Used position. Note that get(Object) operations will modify the underlying Collection. Calling get(Object) inside of an iteration over keys, values, etc. is currently unsupported.
get in interface Mapget in class SequencedHashMapkey - Key to retrievepublic Object put(Object key, Object value)
Removes the key and its Object from the Map.
(Note: this may result in the "Least Recently Used" object being removed from the Map. In that case, the removeLRU() method is called. See javadoc for removeLRU() for more details.)
put in interface Mapput in class SequencedHashMapkey - Key of the Object to add.value - Object to addprotected void removeLRU()
protected void processRemovedLRU(Object key, Object value)
key - key that was removedvalue - value of that key (can be null)public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
SequencedHashMapreadExternal in interface ExternalizablereadExternal in class SequencedHashMapin - the stream to deserialize fromIOException - if the stream raises itClassNotFoundException - if the stream raises itpublic void writeExternal(ObjectOutput out) throws IOException
SequencedHashMapwriteExternal in interface ExternalizablewriteExternal in class SequencedHashMapout - the stream to serialize toIOException - if the stream raises itpublic int getMaximumSize()
public void setMaximumSize(int maximumSize)
maximumSize - New value of property maximumSize.Copyright © The Apache Software Foundation. All Rights Reserved.