org.codehaus.plexus.util

Class FastMap

Implemented Interfaces:
Cloneable, Map, Serializable

public class FastMap
extends java.lang.Object
implements Map, Cloneable, Serializable

This class represents a Map collection with real-time behavior. Unless the map's size exceeds its current capacity, no dynamic memory allocation is ever performed and response time is extremely fast and consistent.

Our benchmark indicates that FastMap.put(key, value) is up to 5x faster than java.util.HashMap.put(key, value). This difference is mostly due to the cost of the Map.Entry allocations that FastMap avoids by recycling its entries (see note below).

FastMap has a predictable iteration order, which is the order in which keys were inserted into the map (similar to java.util.LinkedHashMap collection class).

Applications may change the resizing policy of FastMap by overriding the sizeChanged() method. For example, to improve predictability, automatic resizing can be disabled.

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

Note: To avoid dynamic memory allocations, FastMap maintains an internal pool of Map.Entry objects. The size of the pool is determined by the map's capacity. When an entry is removed from the map, it is automatically restored to the pool.

This class is public domain (not copyrighted).

Version:
5.3, October 31 2003
Author:
Jean-Marie Dautelle

Nested Class Summary

private static class
FastMap.EntryImpl
This class represents a FastMap entry.
private class
FastMap.EntrySet
private class
FastMap.KeySet
private class
FastMap.Values

Field Summary

private int
_capacity
Holds the map's current capacity.
private FastMap.EntryImpl[]
_entries
Holds the map's hash table.
private FastMap.EntrySet
_entrySet
private FastMap.KeySet
_keySet
private FastMap.EntryImpl
_mapFirst
Holds the first map entry (linked list).
private FastMap.EntryImpl
_mapLast
Holds the last map entry (linked list).
private int
_mask
Holds the hash code mask.
private FastMap.EntryImpl
_poolFirst
Holds the first pool entry (linked list).
private int
_size
Holds the current size.
private FastMap.Values
_values

Constructor Summary

FastMap()
Creates a FastMap with a capacity of 256 entries.
FastMap(Map map)
Creates a FastMap, copy of the specified Map.
FastMap(int capacity)
Creates a FastMap with the specified capacity.

Method Summary

private void
addEntry(Object key, Object value)
Adds a new entry for the specified key and value.
int
capacity()
Returns the capacity of this FastMap.
void
clear()
Removes all mappings from this FastMap.
Object
clone()
Returns a shallow copy of this FastMap.
boolean
containsKey(Object key)
Indicates if this FastMap contains a mapping for the specified key.
boolean
containsValue(Object value)
Indicates if this FastMap maps one or more keys to the specified value.
Set
entrySet()
Returns a collection view of the mappings contained in this FastMap.
boolean
equals(Object obj)
Compares the specified object with this FastMap for equality.
Object
get(Object key)
Returns the value to which this FastMap maps the specified key.
Map.Entry
getEntry(Object key)
Returns the entry with the specified key.
int
hashCode()
Returns the hash code value for this FastMap.
private void
initialize(int capacity)
Initializes this instance for the specified capacity.
boolean
isEmpty()
Indicates if this FastMap contains no key-value mappings.
private static int
keyHash(Object key)
Returns the hash code for the specified key.
Set
keySet()
Returns a set view of the keys contained in this FastMap.
Object
put(Object key, Object value)
Associates the specified value with the specified key in this FastMap.
void
putAll(Map map)
Copies all of the mappings from the specified map to this FastMap.
private void
readObject(ObjectInputStream stream)
Requires special handling during de-serialization process.
Object
remove(Object key)
Removes the mapping for this key from this FastMap if present.
private void
removeEntry(FastMap.EntryImpl entry)
Removes the specified entry from the map.
void
setCapacity(int newCapacity)
Changes the current capacity of this FastMap.
int
size()
Returns the number of key-value mappings in this FastMap.
protected void
sizeChanged()
This methods is being called when the size of this FastMap has changed.
String
toString()
Returns a String representation of this FastMap.
Collection
values()
Returns a collection view of the values contained in this FastMap.
private void
writeObject(ObjectOutputStream stream)
Requires special handling during serialization process.

Field Details

_capacity

private int _capacity
Holds the map's current capacity.

_entries

private FastMap.EntryImpl[] _entries
Holds the map's hash table.

_entrySet

private FastMap.EntrySet _entrySet

_keySet

private FastMap.KeySet _keySet

_mapFirst

private FastMap.EntryImpl _mapFirst
Holds the first map entry (linked list).

_mapLast

private FastMap.EntryImpl _mapLast
Holds the last map entry (linked list).

_mask

private int _mask
Holds the hash code mask.

_poolFirst

private FastMap.EntryImpl _poolFirst
Holds the first pool entry (linked list).

_size

private int _size
Holds the current size.

_values

private FastMap.Values _values

Constructor Details

FastMap

public FastMap()
Creates a FastMap with a capacity of 256 entries.

FastMap

public FastMap(Map map)
Creates a FastMap, copy of the specified Map. If the specified map is not an instance of FastMap, the newly created map has a capacity set to the specified map's size. The copy has the same order as the original, regardless of the original map's implementation:
     TreeMap dictionary = ...;
     FastMap dictionaryLookup = new FastMap(dictionary);
 
Parameters:
map - the map whose mappings are to be placed in this map.

FastMap

public FastMap(int capacity)
Creates a FastMap with the specified capacity. Unless the capacity is exceeded, operations on this map do not allocate entries. For optimum performance, the capacity should be of the same order of magnitude or larger than the expected map's size.
Parameters:
capacity - the number of buckets in the hash table; it also defines the number of pre-allocated entries.

Method Details

addEntry

private void addEntry(Object key,
                      Object value)
Adds a new entry for the specified key and value.
Parameters:
key - the entry's key.
value - the entry's value.

capacity

public int capacity()
Returns the capacity of this FastMap. The capacity defines the number of buckets in the hash table, as well as the maximum number of entries the map may contain without allocating memory.
Returns:
this map's capacity.

clear

public void clear()

clone

public Object clone()
Returns a shallow copy of this FastMap. The keys and the values themselves are not cloned.
Returns:
a shallow copy of this map.

containsKey

public boolean containsKey(Object key)
Indicates if this FastMap 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)
Indicates if this FastMap maps one or more keys to the specified value.
Parameters:
value - the value whose presence in this map is to be tested.
Returns:
true if this map maps one or more keys to the specified value.

entrySet

public Set entrySet()
Returns a collection view of the mappings contained in this FastMap. Each element in the returned collection is a Map.Entry. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.
Returns:
a collection view of the mappings contained in this map.

equals

public boolean equals(Object obj)
Compares the specified object with this FastMap for equality. Returns true if the given object is also a map and the two maps represent the same mappings (regardless of collection iteration order).
Parameters:
obj - the object to be compared for equality with this map.
Returns:
true if the specified object is equal to this map; false otherwise.

get

public Object get(Object key)
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 there is no mapping for the key.

getEntry

public Map.Entry getEntry(Object key)
Returns the entry with the specified key.
Parameters:
key - the key whose associated entry is to be returned.
Returns:
the entry for the specified key or null if none.

hashCode

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

initialize

private void initialize(int capacity)
Initializes this instance for the specified capacity. Once initialized, operations on this map should not create new objects (unless the map's size exceeds the specified capacity).
Parameters:
capacity - the initial capacity.

isEmpty

public boolean isEmpty()
Indicates if this FastMap contains no key-value mappings.
Returns:
true if this map contains no key-value mappings; false otherwise.

keyHash

private static int keyHash(Object key)
Returns the hash code for the specified key. The formula being used is identical to the formula used by java.util.HashMap (ensures similar behavior for ill-conditioned hashcode keys).
Parameters:
key - the key to calculate the hashcode for.
Returns:
the hash code for the specified key.

keySet

public Set keySet()
Returns a set view of the keys contained in this FastMap. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.
Returns:
a set 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 FastMap. If the FastMap previously contained a mapping for this key, the old value is replaced.
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 key. A null return can also indicate that the map previously associated null with the specified key.

putAll

public void putAll(Map map)
Parameters:
map - the mappings to be stored in this map.

readObject

private void readObject(ObjectInputStream stream)
            throws IOException,
                   ClassNotFoundException
Requires special handling during de-serialization process.
Parameters:
stream - the object input stream.

remove

public Object remove(Object key)
Parameters:
key - the 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. A null return can also indicate that the map previously associated null with the specified key.

removeEntry

private void removeEntry(FastMap.EntryImpl entry)
Removes the specified entry from the map.
Parameters:
entry - the entry to be removed.

setCapacity

public void setCapacity(int newCapacity)
Changes the current capacity of this FastMap. If the capacity is increased, new entries are allocated and added to the pool. If the capacity is decreased, entries from the pool are deallocated (and are eventually garbage collected). The capacity also determined the number of buckets for the hash table.
Parameters:
newCapacity - the new capacity of this map.

size

public int size()
Returns:
this map's size.

sizeChanged

protected void sizeChanged()
This methods is being called when the size of this FastMap has changed. The default behavior is to double the map's capacity when the map's size reaches the current map's capacity. Sub-class may override this method to implement custom resizing policies or to disable automatic resizing. For example:
     Map fixedCapacityMap = new FastMap(256) { 
           protected sizeChanged() {
               // Do nothing, automatic resizing disabled.
           }
     };

toString

public String toString()
Returns:
this.entrySet().toString();

values

public Collection values()
Returns a collection view of the values contained in this FastMap. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.
Returns:
a collection view of the values contained in this map.

writeObject

private void writeObject(ObjectOutputStream stream)
            throws IOException
Requires special handling during serialization process.
Parameters:
stream - the object output stream.