wt.util
Class Cache

java.lang.Object
  java.util.AbstractMap
      wt.util.Cache

All Implemented Interfaces:

Map

Direct Known Subclasses:

DirtyCache, ManagedCache, ProjectModelCache, ReferenceCache.ObjectReferenceCacheTable.ObjectReferenceCache, ServerAffinityCache, ServerAffinityCache, StandardNmProjMgmtService.PlanModelCache, StandardNmTopicService.ForumModelCache, StatementCache, TeamTemplateCache.CachedTeamTemplates, WrappedPostlessSocket.SocketCache, WrappedSocket.SocketCache

public class Cache

extends AbstractMap

A fixed size, most recently used object cache. The caches size is set at construction, and only the most recently used entries are maintained. Each get or put operation makes that entry the most recently used. When putting new entries, if the cache is full, the least recently used entry is aged out of the cache.

Supported API: true
Extendable: false

Nested Class Summary

protected class	Cache.CacheEntry Default implementation of Map.Entry
(package private) class	Cache.EntrySet Implements a modifiable set based on the entries in this cache
(package private) class	Cache.KeySet

Nested classes inherited from class java.util.AbstractMap

Nested classes inherited from class java.util.Map

Map.Entry

Field Summary

protected int	agedOut
protected int	cacheSize
protected int	count
(package private) Set	entrySet
protected int[]	hashCodes
protected int	hits
protected Object[]	keys
(package private) Set	keySet
private int	leastRecentlyUsed
protected int	misses
protected int	modCount
private int	mostRecentlyUsed
private int[]	newer
private int[]	next
private int[]	older
private int[]	prev
private static String	RESOURCE
protected int	tableSize
protected Object[]	values

Constructor Summary

Cache(int size)
Construct a new fixed-size, most-recently-used cache.

Cache(Map m)

Method Summary

void	clear() Clears the cache.
boolean	containsKey(Object key) Determines if this cache contains the given key
boolean	containsValue(Object value) Determines if this cache contains the given value
protected Map.Entry	createEntry(int index) Used to create the Map.Entry instances stored by this cache
Enumeration	entries() Deprecated. Replaced by values().iterator() Supported API: true
Set	entrySet()
protected int	find(Object key) Protected method that finds existing entry.
Object	get(Object key) Get an entry from the cache.
Object	getAndRemove(Object key) Deprecated. Replaced by remove(Object) Supported API: true
Object	getAndReplace(Object key, Object value) Deprecated. Replaced by put(Object,Object) Supported API: true
Object[]	getKeys() Get an array of the keys in this Cache.
Set	keySet()
protected int	link(Object key) Protected method that finds slot for an existing or new entry.
protected void	overflow(Object key, Object value) Called when an entry is being aged out of the cache.
protected void	print()
Object	put(Object key, Object value) Put an entry in the cache.
Object	remove(Object key) Remove an entry from the cache.
int	size() Get the number of mappings in this cache
String	toString() Returns string representation of the cache.
protected void	touch(int index) Protected method to update age links to make the given entry be the most recently used.
private void	unlink(int index) Private method to unlink an entry from the cache.

Methods inherited from class java.util.AbstractMap

clone, equals, hashCode, isEmpty, putAll, values

Methods inherited from class java.lang.Object

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

Field Detail

RESOURCE

private static final String RESOURCE

See Also:

Constant Field Values

cacheSize

protected int cacheSize

tableSize

protected int tableSize

count

protected int count

keys

protected Object[] keys

values

protected Object[] values

hashCodes

protected int[] hashCodes

hits

protected int hits

misses

protected int misses

agedOut

protected int agedOut

modCount

protected int modCount

mostRecentlyUsed

private int mostRecentlyUsed

leastRecentlyUsed

private int leastRecentlyUsed

newer

private int[] newer

older

private int[] older

next

private int[] next

prev

private int[] prev

entrySet

transient Set entrySet

keySet

transient Set keySet

Constructor Detail

Cache

public Cache(int size)

Construct a new fixed-size, most-recently-used cache. Sparse arrays of ints are used to maintain linked lists in a memory efficient manner - the maximum size supported by this implementation is 715827882.

Supported API: true

Parameters:

size - the maximum number of entries stored in the cache.

Cache

public Cache(Map m)

Method Detail

containsKey

public boolean containsKey(Object key)

Determines if this cache contains the given key

Parameters:

key -

Returns:

boolean

containsValue

public boolean containsValue(Object value)

Determines if this cache contains the given value

Parameters:

value -

Returns:

boolean

size

public int size()

Get the number of mappings in this cache

Returns:

int

get

public Object get(Object key)

Get an entry from the cache. Hit and miss statistics are updated.

Supported API: true

Parameters:

key - the entry key

Returns:

the cached object or null if not found

put

public Object put(Object key,
                  Object value)

Put an entry in the cache. If an entry for the given key already exists, the previous value is discarded. This entry is considered the most recently used.

Supported API: true

Parameters:

key - the entry key

value - the value to associate with the given key

Returns:

The previous value that mapped to the key, or null if there was no previous value

getAndReplace

public Object getAndReplace(Object key,
                            Object value)

Deprecated. Replaced by put(Object,Object)

Supported API: true

Get an entry from the cache and replace it with a new entry. The new entry is considered the most recently used. Hit and miss statistics are updated.

Parameters:

key - the entry key

value - the value to associate with the given key

Returns:

previous value

remove

public Object remove(Object key)

Remove an entry from the cache. Does nothing if the entry is not currently in the cache.

Supported API: true

Parameters:

key - the entry key

getAndRemove

public Object getAndRemove(Object key)

Deprecated. Replaced by remove(Object)

Supported API: true

Get an entry from the cache and remove it at the same time. Does nothing if the entry is not currently in the cache. Hit and miss statistics are updated.

Parameters:

key - the entry key

Returns:

previous value

clear

public void clear()

Clears the cache. All entries are removed.

Supported API: true

find

protected int find(Object key)

Protected method that finds existing entry. Hit and miss statistics are not updated. Most recently used list is not updated.

Supported API: false

Parameters:

key - the entry key

Returns:

index of the entry or 0 if not found

link

protected int link(Object key)

Protected method that finds slot for an existing or new entry. Hit and miss statistics are not updated. Most recently used list is not updated.

Supported API: false

Parameters:

key - the entry key

Returns:

index of the entry

touch

protected void touch(int index)

Protected method to update age links to make the given entry be the most recently used.

Supported API: false

Parameters:

index - the index of the entry

unlink

private void unlink(int index)

Private method to unlink an entry from the cache.

Supported API: false

Parameters:

index - the index of the entry

entries

public Enumeration entries()

Deprecated. Replaced by values().iterator()

Supported API: true

Returns an Enumeration of the values in the cache.

toString

public String toString()

Returns string representation of the cache. The string contains the default string representation of the object plus a summary of the current cache size, hits and misses counts, and aged out entry count.

Supported API: true

overflow

protected void overflow(Object key,
                        Object value)

Called when an entry is being aged out of the cache. Can be overriden by subclasses that want to take some action when an entry is being aged out of the cache due to overflow. It is only called when an entry is aged out due to overflow, not when entries are explicitly removed or the cache is cleared. It is called before the entry is removed from the cache.

Parameters:

key - the entry key

value - the entry value

print

protected void print()

getKeys

public Object[] getKeys()

Get an array of the keys in this Cache. Care should be taken when modifying this array, as it is used by the cache internally.

Returns:

An Object[] of keys. There will likely be null values in the array

See Also:

For a Collection-based view of the keys in this cache

entrySet

public Set entrySet()

Returns:

A set of Map.Entry objects for the mappings in this cache. The Entry objects are reused by the cache, so there is no internal guarantee that the key in a given entry will stay the same over time.

keySet

public Set keySet()

createEntry

protected Map.Entry createEntry(int index)

Used to create the Map.Entry instances stored by this cache

Returns:

Entry