org.mmbase.util
Class LRUHashtable

java.lang.Object
  java.util.Dictionary
      java.util.Hashtable
          org.mmbase.util.LRUHashtable

All Implemented Interfaces:

java.lang.Cloneable, java.util.Map, java.io.Serializable

Direct Known Subclasses:

Cache, MultilevelCacheHandler

public class LRUHashtable

extends java.util.Hashtable

implements java.lang.Cloneable

A hashtable which has a maximum of entries. Old entries are removed when the maximum is reached. This table is used mostly to implement a simple caching system.

Version:

$Id: LRUHashtable.java,v 1.17.2.1 2004/09/07 14:37:24 michiel Exp $

Author:

Rico Jansen, Michiel Meeuwissen

See Also:

Cache, Serialized Form

Nested Class Summary

class	LRUHashtable.LRUEntry Element used to store information from the LRUHashtable.
protected class	LRUHashtable.LRUEntrySet Used by 'entrySet' implementation, to make the Map modifiable.
protected class	LRUHashtable.LRUEntrySetIterator Used by 'entrySet' implementation, to make the Map modifiable.

Constructor Summary

LRUHashtable()
Creates the URL Hashtable with maximum capacity 100, starting capacity 101, and growing capacity 0.75.

LRUHashtable(int size)
Creates the URL Hashtable with starting capacity 101 and growing capacity 0.75.

LRUHashtable(int size, int cap)
Creates the URL Hashtable with growing capacity 0.75.

LRUHashtable(int size, int cap, float lf)
Creates the URL Hashtable.

Method Summary

void	clear() Clears the table.
java.lang.Object	clone() NOT IMPLEMENTED
java.util.Enumeration	elements() Returns an Enumeration on the table's element values.
java.util.Set	entrySet() Returns the entries of this Map.
java.lang.Object	get(java.lang.Object key) Retrieves an element from the table.
int	getCount(java.lang.Object key) Retrieves the count of the object with a certain key.
int	getHits() Returns the number of times an element was succesfully retrieved from the table.
int	getMisses() Returns the number of times an element cpould not be retrieved from the table.
java.util.Enumeration	getOrderedElements() Deprecated. use getOrderedEntries
java.util.Enumeration	getOrderedElements(int maxnumber) Deprecated. use getOrderedEntries
java.util.List	getOrderedEntries() Returns an ordered list of Map.Entry's.
java.util.List	getOrderedEntries(int maxNumber) Returns an ordered list of Map.Entry's.
int	getPuts() Returns the number of times an element was committed to the table.
double	getRatio() Returns the ratio of hits and misses.
int	getSize() Return the maximum size of the table
java.lang.String	getStats() Returns statistics on this table.
java.util.Set	keySet() You should only remove entries from LRUHashtable using the 'remove' function, or using the iterator of entrySet() otherwise the linked list gets messed up.
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Store an element in the table.
java.lang.Object	remove(java.lang.Object key) Remove an element from the table.
void	setSize(int size) Change the maximum size of the table.
int	size() Return the current size of the table
java.lang.String	toString() Returns a description of the table.
java.lang.String	toString(boolean which) Returns a description of the table.
java.util.Collection	values()

Methods inherited from class java.util.Hashtable

contains, containsKey, containsValue, equals, hashCode, isEmpty, keys, putAll, rehash

Methods inherited from class java.lang.Object

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

Constructor Detail

LRUHashtable

public LRUHashtable(int size,
                    int cap,
                    float lf)

Creates the URL Hashtable.

Parameters:

size - the maximum capacity

cap - the starting capacity (used to improve performance)

lf - the amount with which current capacity frows

LRUHashtable

public LRUHashtable(int size,
                    int cap)

Creates the URL Hashtable with growing capacity 0.75.

Parameters:

size - the maximum capacity

cap - the starting capacity (used to improve performance)

LRUHashtable

public LRUHashtable(int size)

Creates the URL Hashtable with starting capacity 101 and growing capacity 0.75.

Parameters:

size - the maximum capacity

LRUHashtable

public LRUHashtable()

Creates the URL Hashtable with maximum capacity 100, starting capacity 101, and growing capacity 0.75.

Method Detail

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)

Store an element in the table.

Specified by:

put in interface java.util.Map

Parameters:

key - the key of the element

value - the value of the element

Returns:

the original value of the element if it existed, null if it could not be found

getCount

public int getCount(java.lang.Object key)

Retrieves the count of the object with a certain key.

Parameters:

key - the key of the element

Returns:

the times the key has been requested

get

public java.lang.Object get(java.lang.Object key)

Retrieves an element from the table.

Specified by:

get in interface java.util.Map

Parameters:

key - the key of the element

Returns:

the value of the element, or null if it could not be found

remove

public java.lang.Object remove(java.lang.Object key)

Remove an element from the table.

Specified by:

remove in interface java.util.Map

Parameters:

key - the key of the element

Returns:

the original value of the element if it existed, null if it could not be found

keySet

public java.util.Set keySet()

You should only remove entries from LRUHashtable using the 'remove' function, or using the iterator of entrySet() otherwise the linked list gets messed up. The keySet of LRUHashtable therefore returns an unmodifiable set.

Specified by:

keySet in interface java.util.Map

Since:

MMBase-1.6.3

entrySet

public java.util.Set entrySet()

Returns the entries of this Map. Modification are reflected.

Specified by:

entrySet in interface java.util.Map

Since:

MMBase-1.6.3

values

public java.util.Collection values()

Specified by:

values in interface java.util.Map

Since:

MMBase-1.6.3

See Also:

keySet()

size

public int size()

Return the current size of the table

Specified by:

size in interface java.util.Map

setSize

public void setSize(int size)

Change the maximum size of the table. This may result in removal of entries in the table.

Parameters:

size - the new desired size

getSize

public int getSize()

Return the maximum size of the table

toString

public java.lang.String toString()

Returns a description of the table. The information shown includes current size, maximum size, ratio of misses and hits, and a description of the underlying hashtable

toString

public java.lang.String toString(boolean which)

Returns a description of the table. The information shown includes current size, maximum size, ratio of misses and hits, and either a description of the underlying hashtable, or a list of all stored values.

Parameters:

which - if true, the stored values are described.

Returns:

a description of the table.

clear

public void clear()

Clears the table.

Specified by:

clear in interface java.util.Map

clone

public java.lang.Object clone()

NOT IMPLEMENTED

elements

public java.util.Enumeration elements()

Returns an Enumeration on the table's element values.

getRatio

public double getRatio()

Returns the ratio of hits and misses. The higher the ratio, the more succesfull the table retrieval is. A value of 1 means every attempt to retrieve data is succesfull, while a value nearing 0 means most times the object requested it is not available. Generally a high ratio means the table can be shrunk, while a low ratio means its size needs to be increased.

Returns:

A double between 0 and 1 or NaN.

getHits

public int getHits()

Returns the number of times an element was succesfully retrieved from the table.

getMisses

public int getMisses()

Returns the number of times an element cpould not be retrieved from the table.

getPuts

public int getPuts()

Returns the number of times an element was committed to the table.

getStats

public java.lang.String getStats()

Returns statistics on this table. The information shown includes number of accesses, ratio of misses and hits, current size, and number of puts.

getOrderedElements

public java.util.Enumeration getOrderedElements()

Deprecated. use getOrderedEntries

getOrderedElements

public java.util.Enumeration getOrderedElements(int maxnumber)

Deprecated. use getOrderedEntries

getOrderedEntries

public java.util.List getOrderedEntries()

Returns an ordered list of Map.Entry's.

Since:

MMBase-1.6

getOrderedEntries

public java.util.List getOrderedEntries(int maxNumber)

Returns an ordered list of Map.Entry's. This can be used to present the contents of the LRU Map.

Since:

MMBase-1.6