org.apache.jcs.utils.struct
Class LRUMap<K,V>

java.lang.Object
  org.apache.jcs.utils.struct.LRUMap<K,V>

All Implemented Interfaces:

Map<K,V>

Direct Known Subclasses:

LRUMapJCS

public class LRUMap<K,V>
extends Object
implements Map<K,V>

This is a simple LRUMap. It implements most of the map methods. It is not recommended that you use any but put, get, remove, and clear.

Children can implement the processRemovedLRU method if they want to handle the removal of the lest recently used item.

This class was abstracted out of the LRU Memory cache. Put, remove, and get should be thread safe. It uses a hashtable and our own double linked list.

Locking is done on the instance.

Author:

aaron smuts

map

protected Map<K,LRUElementDescriptor<K,V>> map

Map where items are stored by key.

LRUMap

public LRUMap()

This creates an unbounded version. Setting the max objects will result in spooling on subsequent puts.

LRUMap

public LRUMap(int maxObjects)

This sets the size limit.

Parameters:

maxObjects -

size

public int size()

This simply returned the number of elements in the map.

Specified by:

size in interface Map<K,V>

See Also:

Map.size()

clear

public void clear()

This removes all the items. It clears the map and the double linked list.

Specified by:

clear in interface Map<K,V>

See Also:

Map.clear()

isEmpty

public boolean isEmpty()

Returns true if the map is empty.

Specified by:

isEmpty in interface Map<K,V>

See Also:

Map.isEmpty()

containsKey

public boolean containsKey(Object key)

Returns true if the map contains an element for the supplied key.

Specified by:

containsKey in interface Map<K,V>

See Also:

Map.containsKey(java.lang.Object)

containsValue

public boolean containsValue(Object value)

This is an expensive operation that determines if the object supplied is mapped to any key.

Specified by:

containsValue in interface Map<K,V>

See Also:

Map.containsValue(java.lang.Object)

values

public Collection<V> values()

Specified by:

values in interface Map<K,V>

Returns:

map.values();

putAll

public void putAll(Map<? extends K,? extends V> source)

Specified by:

putAll in interface Map<K,V>

Parameters:

source -

get

public V get(Object key)

Specified by:

get in interface Map<K,V>

Parameters:

key -

Returns:

Object

getQuiet

public V getQuiet(Object key)

This gets an element out of the map without adjusting it's posisiton in the LRU. In other words, this does not count as being used. If the element is the last item in the list, it will still be the last itme in the list.

Parameters:

key -

Returns:

Object

remove

public V remove(Object key)

Specified by:

remove in interface Map<K,V>

Parameters:

key -

Returns:

Object removed

put

public V put(K key,
             V value)

Specified by:

put in interface Map<K,V>

Parameters:

key -

value -

Returns:

Object

dumpCacheEntries

public void dumpCacheEntries()

Dump the cache entries from first to list for debugging.

dumpMap

public void dumpMap()

Dump the cache map for debugging.

verifyCache

protected void verifyCache()

Checks to see if all the items that should be in the cache are. Checks consistency between List and map.

verifyCache

protected void verifyCache(Object key)

Logs an error is an element that should be in the cache is not.

Parameters:

key -

processRemovedLRU

protected void processRemovedLRU(K key,
                                 V value)

This is called when an item is removed from the LRU. We just log some information.

Children can implement this method for special behavior.

Parameters:

key -

value -

setChunkSize

public void setChunkSize(int chunkSize)

The chunk size is the number of items to remove when the max is reached. By default it is 1.

Parameters:

chunkSize - The chunkSize to set.

getChunkSize

public int getChunkSize()

Returns:

Returns the chunkSize.

getStatistics

public IStats getStatistics()

Returns:

IStats

entrySet

public Set<Map.Entry<K,V>> entrySet()

This returns a set of entries. Our LRUMapEntry is used since the value stored in the underlying map is a node in the double linked list. We wouldn't want to return this to the client, so we construct a new entry with the payload of the node.

TODO we should return out own set wrapper, so we can avoid the extra object creation if it isn't necessary.

Specified by:

entrySet in interface Map<K,V>

See Also:

Map.entrySet()

keySet

public Set<K> keySet()

Specified by:

keySet in interface Map<K,V>

Returns:

map.keySet();

getMaxObjects

public int getMaxObjects()

Returns:

the max objects size.