LRUHashMap

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raining.server
Class LRUHashMap

java.lang.Object
  java.util.AbstractMap
      java.util.HashMap
          java.util.LinkedHashMap
              raining.server.LRUHashMap

All Implemented Interfaces:: java.lang.Cloneable, java.util.Map, java.io.Serializable

class LRUHashMap
extends java.util.LinkedHashMap

An extension of LinkedHashMap that removes eldest accessed entry after crossing the max_entries. Pls note that each access of an LRU obviously changes the underlying list. I need to do some performance testing on this, against some other implementation, or a home grown one.

Nested Class Summary

Nested classes inherited from class java.util.LinkedHashMap

Nested classes inherited from class java.util.HashMap

Nested classes inherited from class java.util.AbstractMap

Nested classes inherited from class java.util.Map

java.util.Map.Entry

Field Summary

private int max_entries


Fields inherited from class java.util.LinkedHashMap

Fields inherited from class java.util.HashMap

Fields inherited from class java.util.AbstractMap

Constructor Summary

LRUHashMap(int initial, int max_entries, float loadfactor, boolean lru)


Method Summary

protected boolean removeEldestEntry(java.util.Map.Entry eldest)
          Returns true if this map should remove the eldest entry.

Methods inherited from class java.util.LinkedHashMap

clear, containsValue, get

Methods inherited from class java.util.HashMap

clone, containsKey, entrySet, isEmpty, keySet, put, putAll, remove, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

equals, hashCode

Field Detail

max_entries

private int max_entries

Constructor Detail

LRUHashMap

public LRUHashMap(int initial,
                  int max_entries,
                  float loadfactor,
                  boolean lru)

Method Detail

removeEldestEntry

protected boolean removeEldestEntry(java.util.Map.Entry eldest)

Description copied from class: java.util.LinkedHashMap

Returns true if this map should remove the eldest entry. This method is invoked by all calls to put and putAll which place a new entry in the map, providing the implementer an opportunity to remove the eldest entry any time a new one is added. This can be used to save memory usage of the hashtable, as well as emulating a cache, by deleting stale entries.

For example, to keep the Map limited to 100 entries, override as follows:

 private static final int MAX_ENTRIES = 100;
 protected boolean removeEldestEntry(Map.Entry eldest)
 {
   return size() > MAX_ENTRIES;
 }

Typically, this method does not modify the map, but just uses the return value as an indication to put whether to proceed. However, if you override it to modify the map, you must return false (indicating that put should leave the modified map alone), or you face unspecified behavior. Remember that in access-order mode, even calling get is a structural modification, but using the collections views (such as keySet) is not.

This method is called after the eldest entry has been inserted, so if put was called on a previously empty map, the eldest entry is the one you just put in! The default implementation just returns false, so that this map always behaves like a normal one with unbounded growth.