org.apache.commons.collections
Class LRUMap
- Cloneable, Externalizable, Map
public class LRUMap
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().
$Revision: 1.23 $ $Date: 2004/02/18 01:15:42 $LRUMap() - Default constructor, primarily for the purpose of
de-externalization.
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LRUMap(int i) - Create a new LRUMap with a maximum capacity of i.
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Object | get(Object key) - Get the value for a key from the Map.
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int | getMaximumSize() - Getter for property maximumSize.
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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.
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Object | put(Object key, Object value) - Removes the key and its Object from the Map.
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void | readExternal(ObjectInput in) - Deserializes this map from the given stream.
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protected void | removeLRU() - This method is used internally by the class for
finding and removing the LRU Object.
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void | setMaximumSize(int maximumSize) - Setter for property maximumSize.
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void | writeExternal(ObjectOutput out) - Serializes this map to the given stream.
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clear , clone , containsKey , containsValue , entrySet , equals , get , get , getFirst , getFirstKey , getFirstValue , getLast , getLastKey , getLastValue , getValue , hashCode , indexOf , isEmpty , iterator , keySet , lastIndexOf , put , putAll , readExternal , remove , remove , sequence , size , toString , values , writeExternal |
LRUMap
public LRUMap()
Default constructor, primarily for the purpose of
de-externalization. This constructors sets a default
LRU limit of 100 keys, but this value may be overridden
internally as a result of de-externalization.
LRUMap
public LRUMap(int i)
Create a new LRUMap with a maximum capacity of i.
Once i capacity is achieved, subsequent gets
and puts will push keys out of the map. See .
i
- Maximum capacity of the LRUMap
get
public 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 SequencedHashMap
- Returns the value. Returns null if the key has a
null value or if the key has no value.
getMaximumSize
public int getMaximumSize()
Getter for property maximumSize.
- Value of property maximumSize.
processRemovedLRU
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. By default,
this method does nothing.
key
- key that was removedvalue
- value of that key (can be null)
put
public 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 SequencedHashMap
key
- Key of the Object to add.value
- Object to add
readExternal
public void readExternal(ObjectInput in)
throws IOException,
ClassNotFoundException
Deserializes this map from the given stream.
- readExternal in interface SequencedHashMap
in
- the stream to deserialize from
removeLRU
protected void removeLRU()
This method is used internally by the class for
finding and removing the LRU Object.
setMaximumSize
public void setMaximumSize(int maximumSize)
Setter for property maximumSize.
maximumSize
- New value of property maximumSize.
writeExternal
public void writeExternal(ObjectOutput out)
throws IOException
Serializes this map to the given stream.
- writeExternal in interface SequencedHashMap
out
- the stream to serialize to
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