org.codehaus.plexus.util

Class CachedMap

public final class CachedMap extends Object implements Map

This class provides cache access to Map collections.

Instance of this class can be used as "proxy" for any collection implementing the java.util.Map interface.

Typically, CachedMap are used to accelerate access to large collections when the access to the collection is not evenly distributed (associative cache). The performance gain is about 50% for the fastest hash map collections (e.g. FastMap). For slower collections such as java.util.TreeMap, non-resizable FastMap (real-time) or database access, performance can be of several orders of magnitude.

Note: The keys used to access elements of a CachedMap do not need to be immutable as they are not stored in the cache (only keys specified by the CachedMap method are). In other words, access can be performed using mutable keys as long as these keys can be compared for equality with the real map's keys (e.g. same hashCode values).

This implementation is not synchronized. Multiple threads accessing or modifying the collection must be synchronized externally.

This class is public domain (not copyrighted).

Version: 5.3, October 30, 2003

Author: Jean-Marie Dautelle

Constructor Summary
CachedMap()
Creates a cached map backed by a FastMap.
CachedMap(int cacheSize)
Creates a cached map backed by a FastMap and having the specified cache size.
CachedMap(int cacheSize, Map backingMap)
Creates a cached map backed by the specified map and having the specified cache size.
Method Summary
voidclear()
Removes all mappings from this map (optional operation).
booleancontainsKey(Object key)
Indicates if this map contains a mapping for the specified key.
booleancontainsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
SetentrySet()
Returns an unmodifiable view of the mappings contained in this map.
booleanequals(Object o)
Compares the specified object with this map for equality.
voidflush()
Flushes the key/value pairs being cached.
Objectget(Object key)
Returns the value to which this map maps the specified key.
MapgetBackingMap()
Returns the backing map.
intgetCacheSize()
Returns the actual cache size.
inthashCode()
Returns the hash code value for this map.
booleanisEmpty()
Returns true if this map contains no key-value mappings.
SetkeySet()
Returns an unmodifiable view of the keys contained in this map.
Objectput(Object key, Object value)
Associates the specified value with the specified key in this map.
voidputAll(Map map)
Copies all of the mappings from the specified map to this map (optional operation).
Objectremove(Object key)
Removes the mapping for this key from this map if it is present.
intsize()
Returns the number of key-value mappings in this map.
Collectionvalues()
Returns an unmodifiable view of the values contained in this map.

Constructor Detail

CachedMap

public CachedMap()
Creates a cached map backed by a FastMap. The default cache size and map capacity is set to 256 entries.

CachedMap

public CachedMap(int cacheSize)
Creates a cached map backed by a FastMap and having the specified cache size.

Parameters: cacheSize the cache size, the actual cache size is the first power of 2 greater or equal to cacheSize. This is also the initial capacity of the backing map.

CachedMap

public CachedMap(int cacheSize, Map backingMap)
Creates a cached map backed by the specified map and having the specified cache size. In order to maitain cache veracity, it is critical that all update to the backing map is accomplished through the CachedMap instance; otherwise CachedMap has to be called.

Parameters: cacheSize the cache size, the actual cache size is the first power of 2 greater or equal to cacheSize. backingMap the backing map to be "wrapped" in a cached map.

Method Detail

clear

public void clear()
Removes all mappings from this map (optional operation). This method automatically flushes the cache.

Throws: UnsupportedOperationException if clear is not supported by the backing map.

containsKey

public boolean containsKey(Object key)
Indicates if this map contains a mapping for the specified key.

Parameters: key the key whose presence in this map is to be tested.

Returns: true if this map contains a mapping for the specified key; false otherwise.

containsValue

public boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value.

Parameters: value value whose presence in this map is to be tested.

Returns: true if this map maps one or more keys to the specified value.

Throws: ClassCastException if the value is of an inappropriate type for the backing map (optional). NullPointerException if the value is null and the backing map does not not permit null values.

entrySet

public Set entrySet()
Returns an unmodifiable view of the mappings contained in this map. Each element in the returned set is a Map.Entry.

Returns: an unmodifiable view of the mappings contained in this map.

equals

public boolean equals(Object o)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two Maps represent the same mappings.

Parameters: o object to be compared for equality with this map.

Returns: true if the specified object is equal to this map.

flush

public void flush()
Flushes the key/value pairs being cached. This method should be called if the backing map is externally modified.

get

public Object get(Object key)
Returns the value to which this map maps the specified key. First, the cache is being checked, then if the cache does not contains the specified key, the backing map is accessed and the key/value pair is stored in the cache.

Parameters: key the key whose associated value is to be returned.

Returns: the value to which this map maps the specified key, or null if the map contains no mapping for this key.

Throws: ClassCastException if the key is of an inappropriate type for the backing map (optional). NullPointerException if the key is null.

getBackingMap

public Map getBackingMap()
Returns the backing map. If the backing map is modified directly, this CachedMap has to be flushed.

Returns: the backing map.

See Also: CachedMap

getCacheSize

public int getCacheSize()
Returns the actual cache size.

Returns: the cache size (power of 2).

hashCode

public int hashCode()
Returns the hash code value for this map.

Returns: the hash code value for this map.

isEmpty

public boolean isEmpty()
Returns true if this map contains no key-value mappings.

Returns: true if this map contains no key-value mappings.

keySet

public Set keySet()
Returns an unmodifiable view of the keys contained in this map.

Returns: an unmodifiable view of the keys contained in this map.

put

public Object put(Object key, Object value)
Associates the specified value with the specified key in this map.

Parameters: key the key with which the specified value is to be associated. value the value to be associated with the specified key.

Returns: the previous value associated with specified key, or null if there was no mapping for the key.

Throws: UnsupportedOperationException if the put operation is not supported by the backing map. ClassCastException if the class of the specified key or value prevents it from being stored in this map. IllegalArgumentException if some aspect of this key or value prevents it from being stored in this map. NullPointerException if the key is null.

putAll

public void putAll(Map map)
Copies all of the mappings from the specified map to this map (optional operation). This method automatically flushes the cache.

Parameters: map the mappings to be stored in this map.

Throws: UnsupportedOperationException if the putAll method is not supported by the backing map. ClassCastException if the class of a key or value in the specified map prevents it from being stored in this map. IllegalArgumentException some aspect of a key or value in the specified map prevents it from being stored in this map. NullPointerException the specified map is null, or if the backing map does not permit null keys or values, and the specified map contains null keys or values.

remove

public Object remove(Object key)
Removes the mapping for this key from this map if it is present.

Parameters: key key whose mapping is to be removed from the map.

Returns: previous value associated with specified key, or null if there was no mapping for key.

Throws: ClassCastException if the key is of an inappropriate type for the backing map (optional). NullPointerException if the key is null. UnsupportedOperationException if the remove method is not supported by the backing map.

size

public int size()
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns: the number of key-value mappings in this map.

values

public Collection values()
Returns an unmodifiable view of the values contained in this map.

Returns: an unmodifiable view of the values contained in this map.

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