com.goldencode.cache

Class LFUAgingCache.LFUEntry<K,V>

java.lang.Object

com.goldencode.cache.Cache.Entry<K,V>

com.goldencode.cache.LFUAgingCache.LFUEntry<K,V>

Type Parameters:

K - Hashable key

V - Cached value

All Implemented Interfaces:

java.lang.Comparable<Cache.Entry<K,V>>

Enclosing class:

LFUAgingCache<K,V>

private static class LFUAgingCache.LFUEntry<K,V>
extends Cache.Entry<K,V>
implements java.lang.Comparable<Cache.Entry<K,V>>

A sortable entry containing the hashable key and value of a cache entry. The entry's natural order is determined by the number of times this entry has been retrieved from the cache (its hit count), and by how recently the last retrieval was. If these values match those of another entry exactly, a unique identifier is used as an arbitrary but consistent tie breaker. This ensures each entry is unique and none are excluded as duplicates due to set semantics. Less desirable elements (those to be expired first) are sorted ahead of more desirable elements (those to be retained longer).

Field Summary

Fields

Modifier and Type	Field and Description
private int	hits Hit count, the number of times this entry has been used/retrieved
private int	id Internal identifier
private long	lastAccess Timestamp of last time this element was accessed (created or retrieved)
private static int	nextID Next available entry identifier

Constructor Summary

Constructors

Constructor and Description
LFUEntry(K key, V value) Constructor.

Method Summary

Modifier and Type	Method and Description
private void	access() Increment the hit count for this entry and record the timestamp of this access.
int	compareTo(Cache.Entry<K,V> n) Compare this entry to another.
boolean	equals(java.lang.Object o) An implementation of equivalence checking consistent with compareTo(Entry).

Methods inherited from class com.goldencode.cache.Cache.Entry

getKey, getValue

Methods inherited from class java.lang.Object

clone, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

nextID

private static int nextID

Next available entry identifier

id

private final int id

Internal identifier

hits

private int hits

Hit count, the number of times this entry has been used/retrieved

lastAccess

private long lastAccess

Timestamp of last time this element was accessed (created or retrieved)

Constructor Detail

LFUEntry

LFUEntry(K key,
         V value)

Constructor. Sets initial access time to now, and hit count to 0.

Parameters:

key - Hashable key.

value - Cached value.

Method Detail

compareTo

public int compareTo(Cache.Entry<K,V> n)

Compare this entry to another. An entry with a higher hit count sorts higher than that with a lower hit count. If two entries have the same hit count, that which has more recently been accessed (created or retrieved) sorts higher. If two entries have the same hit count and last access time (should be quite a rare occurrence), a unique ID will be used to force an arbitrary sort order. This last comparison is ensure uniqueness among entries so that the set does not exclude any entries.

This algorithm generally leaves the least desirable element first in the sorted result.

Specified by:

compareTo in interface java.lang.Comparable<Cache.Entry<K,V>>

equals

public boolean equals(java.lang.Object o)

An implementation of equivalence checking consistent with compareTo(Entry).

Overrides:

equals in class java.lang.Object

Parameters:

o - Object with which to compare this instance.

Returns:

true if o is equivalent to this instance, else false.

access

private void access()

Increment the hit count for this entry and record the timestamp of this access.