org.apache.commons.collections.map

Class AbstractHashedMap

public class AbstractHashedMap extends AbstractMap implements IterableMap

An abstract implementation of a hash-based map which provides numerous points for subclasses to override.

This class implements all the features necessary for a subclass hash-based map. Key-value entries are stored in instances of the HashEntry class, which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

NOTE: From Commons Collections 3.1 this class extends AbstractMap. This is to provide backwards compatibility for ReferenceMap between v3.0 and v3.1. This extends clause will be removed in v4.0.

Since: Commons Collections 3.0

Version: $Revision: 171349 $ $Date: 2005-05-22 18:48:56 +0100 (Sun, 22 May 2005) $

Author: java util HashMap Stephen Colebourne Christian Siefkes

Nested Class Summary
protected static classAbstractHashedMap.EntrySet
EntrySet implementation.
protected static classAbstractHashedMap.EntrySetIterator
EntrySet iterator.
protected static classAbstractHashedMap.HashEntry
HashEntry used to store the data.
protected abstract static classAbstractHashedMap.HashIterator
Base Iterator
protected static classAbstractHashedMap.HashMapIterator
MapIterator implementation.
protected static classAbstractHashedMap.KeySet
KeySet implementation.
protected static classAbstractHashedMap.KeySetIterator
KeySet iterator.
protected static classAbstractHashedMap.Values
Values implementation.
protected static classAbstractHashedMap.ValuesIterator
Values iterator.
Field Summary
protected AbstractHashedMap.HashEntry[]data
Map entries
protected static intDEFAULT_CAPACITY
The default capacity to use
protected static floatDEFAULT_LOAD_FACTOR
The default load factor to use
protected static intDEFAULT_THRESHOLD
The default threshold to use
protected AbstractHashedMap.EntrySetentrySet
Entry set
protected static StringGETKEY_INVALID
protected static StringGETVALUE_INVALID
protected AbstractHashedMap.KeySetkeySet
Key set
protected floatloadFactor
Load factor, normally 0.75
protected intmodCount
Modification count for iterators
protected static intMAXIMUM_CAPACITY
The maximum capacity allowed
protected static StringNO_NEXT_ENTRY
protected static StringNO_PREVIOUS_ENTRY
protected static ObjectNULL
An object for masking null
protected static StringREMOVE_INVALID
protected intsize
The size of the map
protected static StringSETVALUE_INVALID
protected intthreshold
Size at which to rehash
protected AbstractHashedMap.Valuesvalues
Values
Constructor Summary
protected AbstractHashedMap()
Constructor only used in deserialization, do not use otherwise.
protected AbstractHashedMap(int initialCapacity, float loadFactor, int threshold)
Constructor which performs no validation on the passed in parameters.
protected AbstractHashedMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity and default load factor.
protected AbstractHashedMap(int initialCapacity, float loadFactor)
Constructs a new, empty map with the specified initial capacity and load factor.
protected AbstractHashedMap(Map map)
Constructor copying elements from another map.
Method Summary
protected voidaddEntry(AbstractHashedMap.HashEntry entry, int hashIndex)
Adds an entry into this map.
protected voidaddMapping(int hashIndex, int hashCode, Object key, Object value)
Adds a new key-value mapping into this map.
protected intcalculateNewCapacity(int proposedCapacity)
Calculates the new capacity of the map.
protected intcalculateThreshold(int newCapacity, float factor)
Calculates the new threshold of the map, where it will be resized.
protected voidcheckCapacity()
Checks the capacity of the map and enlarges it if necessary.
voidclear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
protected Objectclone()
Clones the map without cloning the keys or values.
booleancontainsKey(Object key)
Checks whether the map contains the specified key.
booleancontainsValue(Object value)
Checks whether the map contains the specified value.
protected ObjectconvertKey(Object key)
Converts input keys to another object for storage in the map.
protected AbstractHashedMap.HashEntrycreateEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)
Creates an entry to store the key-value data.
protected IteratorcreateEntrySetIterator()
Creates an entry set iterator.
protected IteratorcreateKeySetIterator()
Creates a key set iterator.
protected IteratorcreateValuesIterator()
Creates a values iterator.
protected voiddestroyEntry(AbstractHashedMap.HashEntry entry)
Kills an entry ready for the garbage collector.
protected voiddoReadObject(ObjectInputStream in)
Reads the map data from the stream.
protected voiddoWriteObject(ObjectOutputStream out)
Writes the map data to the stream.
protected voidensureCapacity(int newCapacity)
Changes the size of the data structure to the capacity proposed.
protected intentryHashCode(AbstractHashedMap.HashEntry entry)
Gets the hashCode field from a HashEntry.
protected ObjectentryKey(AbstractHashedMap.HashEntry entry)
Gets the key field from a HashEntry.
protected AbstractHashedMap.HashEntryentryNext(AbstractHashedMap.HashEntry entry)
Gets the next field from a HashEntry.
SetentrySet()
Gets the entrySet view of the map.
protected ObjectentryValue(AbstractHashedMap.HashEntry entry)
Gets the value field from a HashEntry.
booleanequals(Object obj)
Compares this map with another.
Objectget(Object key)
Gets the value mapped to the key specified.
protected AbstractHashedMap.HashEntrygetEntry(Object key)
Gets the entry mapped to the key specified.
protected inthash(Object key)
Gets the hash code for the key specified.
inthashCode()
Gets the standard Map hashCode.
protected inthashIndex(int hashCode, int dataSize)
Gets the index into the data storage for the hashCode specified.
protected voidinit()
Initialise subclasses during construction, cloning or deserialization.
booleanisEmpty()
Checks whether the map is currently empty.
protected booleanisEqualKey(Object key1, Object key2)
Compares two keys, in internal converted form, to see if they are equal.
protected booleanisEqualValue(Object value1, Object value2)
Compares two values, in external form, to see if they are equal.
SetkeySet()
Gets the keySet view of the map.
MapIteratormapIterator()
Gets an iterator over the map.
Objectput(Object key, Object value)
Puts a key-value mapping into this map.
voidputAll(Map map)
Puts all the values from the specified map into this map.
Objectremove(Object key)
Removes the specified mapping from this map.
protected voidremoveEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)
Removes an entry from the chain stored in a particular index.
protected voidremoveMapping(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)
Removes a mapping from the map.
protected voidreuseEntry(AbstractHashedMap.HashEntry entry, int hashIndex, int hashCode, Object key, Object value)
Reuses an existing key-value mapping, storing completely new data.
intsize()
Gets the size of the map.
StringtoString()
Gets the map as a String.
protected voidupdateEntry(AbstractHashedMap.HashEntry entry, Object newValue)
Updates an existing key-value mapping to change the value.
Collectionvalues()
Gets the values view of the map.

Field Detail

data

protected transient AbstractHashedMap.HashEntry[] data
Map entries

DEFAULT_CAPACITY

protected static final int DEFAULT_CAPACITY
The default capacity to use

DEFAULT_LOAD_FACTOR

protected static final float DEFAULT_LOAD_FACTOR
The default load factor to use

DEFAULT_THRESHOLD

protected static final int DEFAULT_THRESHOLD
The default threshold to use

entrySet

protected transient AbstractHashedMap.EntrySet entrySet
Entry set

GETKEY_INVALID

protected static final String GETKEY_INVALID

GETVALUE_INVALID

protected static final String GETVALUE_INVALID

keySet

protected transient AbstractHashedMap.KeySet keySet
Key set

loadFactor

protected transient float loadFactor
Load factor, normally 0.75

modCount

protected transient int modCount
Modification count for iterators

MAXIMUM_CAPACITY

protected static final int MAXIMUM_CAPACITY
The maximum capacity allowed

NO_NEXT_ENTRY

protected static final String NO_NEXT_ENTRY

NO_PREVIOUS_ENTRY

protected static final String NO_PREVIOUS_ENTRY

NULL

protected static final Object NULL
An object for masking null

REMOVE_INVALID

protected static final String REMOVE_INVALID

size

protected transient int size
The size of the map

SETVALUE_INVALID

protected static final String SETVALUE_INVALID

threshold

protected transient int threshold
Size at which to rehash

values

protected transient AbstractHashedMap.Values values
Values

Constructor Detail

AbstractHashedMap

protected AbstractHashedMap()
Constructor only used in deserialization, do not use otherwise.

AbstractHashedMap

protected AbstractHashedMap(int initialCapacity, float loadFactor, int threshold)
Constructor which performs no validation on the passed in parameters.

Parameters: initialCapacity the initial capacity, must be a power of two loadFactor the load factor, must be > 0.0f and generally < 1.0f threshold the threshold, must be sensible

AbstractHashedMap

protected AbstractHashedMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity and default load factor.

Parameters: initialCapacity the initial capacity

Throws: IllegalArgumentException if the initial capacity is less than one

AbstractHashedMap

protected AbstractHashedMap(int initialCapacity, float loadFactor)
Constructs a new, empty map with the specified initial capacity and load factor.

Parameters: initialCapacity the initial capacity loadFactor the load factor

Throws: IllegalArgumentException if the initial capacity is less than one IllegalArgumentException if the load factor is less than or equal to zero

AbstractHashedMap

protected AbstractHashedMap(Map map)
Constructor copying elements from another map.

Parameters: map the map to copy

Throws: NullPointerException if the map is null

Method Detail

addEntry

protected void addEntry(AbstractHashedMap.HashEntry entry, int hashIndex)
Adds an entry into this map.

This implementation adds the entry to the data storage table. Subclasses could override to handle changes to the map.

Parameters: entry the entry to add hashIndex the index into the data array to store at

addMapping

protected void addMapping(int hashIndex, int hashCode, Object key, Object value)
Adds a new key-value mapping into this map.

This implementation calls createEntry(), addEntry() and checkCapacity(). It also handles changes to modCount and size. Subclasses could override to fully control adds to the map.

Parameters: hashIndex the index into the data array to store at hashCode the hash code of the key to add key the key to add value the value to add

calculateNewCapacity

protected int calculateNewCapacity(int proposedCapacity)
Calculates the new capacity of the map. This implementation normalizes the capacity to a power of two.

Parameters: proposedCapacity the proposed capacity

Returns: the normalized new capacity

calculateThreshold

protected int calculateThreshold(int newCapacity, float factor)
Calculates the new threshold of the map, where it will be resized. This implementation uses the load factor.

Parameters: newCapacity the new capacity factor the load factor

Returns: the new resize threshold

checkCapacity

protected void checkCapacity()
Checks the capacity of the map and enlarges it if necessary.

This implementation uses the threshold to check if the map needs enlarging

clear

public void clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.

clone

protected Object clone()
Clones the map without cloning the keys or values.

To implement clone(), a subclass must implement the Cloneable interface and make this method public.

Returns: a shallow clone

containsKey

public boolean containsKey(Object key)
Checks whether the map contains the specified key.

Parameters: key the key to search for

Returns: true if the map contains the key

containsValue

public boolean containsValue(Object value)
Checks whether the map contains the specified value.

Parameters: value the value to search for

Returns: true if the map contains the value

convertKey

protected Object convertKey(Object key)
Converts input keys to another object for storage in the map. This implementation masks nulls. Subclasses can override this to perform alternate key conversions.

The reverse conversion can be changed, if required, by overriding the getKey() method in the hash entry.

Parameters: key the key convert

Returns: the converted key

createEntry

protected AbstractHashedMap.HashEntry createEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)
Creates an entry to store the key-value data.

This implementation creates a new HashEntry instance. Subclasses can override this to return a different storage class, or implement caching.

Parameters: next the next entry in sequence hashCode the hash code to use key the key to store value the value to store

Returns: the newly created entry

createEntrySetIterator

protected Iterator createEntrySetIterator()
Creates an entry set iterator. Subclasses can override this to return iterators with different properties.

Returns: the entrySet iterator

createKeySetIterator

protected Iterator createKeySetIterator()
Creates a key set iterator. Subclasses can override this to return iterators with different properties.

Returns: the keySet iterator

createValuesIterator

protected Iterator createValuesIterator()
Creates a values iterator. Subclasses can override this to return iterators with different properties.

Returns: the values iterator

destroyEntry

protected void destroyEntry(AbstractHashedMap.HashEntry entry)
Kills an entry ready for the garbage collector.

This implementation prepares the HashEntry for garbage collection. Subclasses can override this to implement caching (override clear as well).

Parameters: entry the entry to destroy

doReadObject

protected void doReadObject(ObjectInputStream in)
Reads the map data from the stream. This method must be overridden if a subclass must be setup before put() is used.

Serialization is not one of the JDK's nicest topics. Normal serialization will initialise the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the put() method on read can be affected by subclass state.

The solution adopted here is to deserialize the state data of this class in this protected method. This method must be called by the readObject() of the first serializable subclass.

Subclasses may override if the subclass has a specific field that must be present before put() or calculateThreshold() will work correctly.

Parameters: in the input stream

doWriteObject

protected void doWriteObject(ObjectOutputStream out)
Writes the map data to the stream. This method must be overridden if a subclass must be setup before put() is used.

Serialization is not one of the JDK's nicest topics. Normal serialization will initialise the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the put() method on read can be affected by subclass state.

The solution adopted here is to serialize the state data of this class in this protected method. This method must be called by the writeObject() of the first serializable subclass.

Subclasses may override if they have a specific field that must be present on read before this implementation will work. Generally, the read determines what must be serialized here, if anything.

Parameters: out the output stream

ensureCapacity

protected void ensureCapacity(int newCapacity)
Changes the size of the data structure to the capacity proposed.

Parameters: newCapacity the new capacity of the array (a power of two, less or equal to max)

entryHashCode

protected int entryHashCode(AbstractHashedMap.HashEntry entry)
Gets the hashCode field from a HashEntry. Used in subclasses that have no visibility of the field.

Parameters: entry the entry to query, must not be null

Returns: the hashCode field of the entry

Throws: NullPointerException if the entry is null

Since: Commons Collections 3.1

entryKey

protected Object entryKey(AbstractHashedMap.HashEntry entry)
Gets the key field from a HashEntry. Used in subclasses that have no visibility of the field.

Parameters: entry the entry to query, must not be null

Returns: the key field of the entry

Throws: NullPointerException if the entry is null

Since: Commons Collections 3.1

entryNext

protected AbstractHashedMap.HashEntry entryNext(AbstractHashedMap.HashEntry entry)
Gets the next field from a HashEntry. Used in subclasses that have no visibility of the field.

Parameters: entry the entry to query, must not be null

Returns: the next field of the entry

Throws: NullPointerException if the entry is null

Since: Commons Collections 3.1

entrySet

public Set entrySet()
Gets the entrySet view of the map. Changes made to the view affect this map. To simply iterate through the entries, use mapIterator.

Returns: the entrySet view

entryValue

protected Object entryValue(AbstractHashedMap.HashEntry entry)
Gets the value field from a HashEntry. Used in subclasses that have no visibility of the field.

Parameters: entry the entry to query, must not be null

Returns: the value field of the entry

Throws: NullPointerException if the entry is null

Since: Commons Collections 3.1

equals

public boolean equals(Object obj)
Compares this map with another.

Parameters: obj the object to compare to

Returns: true if equal

get

public Object get(Object key)
Gets the value mapped to the key specified.

Parameters: key the key

Returns: the mapped value, null if no match

getEntry

protected AbstractHashedMap.HashEntry getEntry(Object key)
Gets the entry mapped to the key specified.

This method exists for subclasses that may need to perform a multi-step process accessing the entry. The public methods in this class don't use this method to gain a small performance boost.

Parameters: key the key

Returns: the entry, null if no match

hash

protected int hash(Object key)
Gets the hash code for the key specified. This implementation uses the additional hashing routine from JDK1.4. Subclasses can override this to return alternate hash codes.

Parameters: key the key to get a hash code for

Returns: the hash code

hashCode

public int hashCode()
Gets the standard Map hashCode.

Returns: the hash code defined in the Map interface

hashIndex

protected int hashIndex(int hashCode, int dataSize)
Gets the index into the data storage for the hashCode specified. This implementation uses the least significant bits of the hashCode. Subclasses can override this to return alternate bucketing.

Parameters: hashCode the hash code to use dataSize the size of the data to pick a bucket from

Returns: the bucket index

init

protected void init()
Initialise subclasses during construction, cloning or deserialization.

isEmpty

public boolean isEmpty()
Checks whether the map is currently empty.

Returns: true if the map is currently size zero

isEqualKey

protected boolean isEqualKey(Object key1, Object key2)
Compares two keys, in internal converted form, to see if they are equal. This implementation uses the equals method and assumes neither key is null. Subclasses can override this to match differently.

Parameters: key1 the first key to compare passed in from outside key2 the second key extracted from the entry via entry.key

Returns: true if equal

isEqualValue

protected boolean isEqualValue(Object value1, Object value2)
Compares two values, in external form, to see if they are equal. This implementation uses the equals method and assumes neither value is null. Subclasses can override this to match differently.

Parameters: value1 the first value to compare passed in from outside value2 the second value extracted from the entry via getValue()

Returns: true if equal

keySet

public Set keySet()
Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator.

Returns: the keySet view

mapIterator

public MapIterator mapIterator()
Gets an iterator over the map. Changes made to the iterator affect this map.

A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map.Entry object.

Returns: the map iterator

put

public Object put(Object key, Object value)
Puts a key-value mapping into this map.

Parameters: key the key to add value the value to add

Returns: the value previously mapped to this key, null if none

putAll

public void putAll(Map map)
Puts all the values from the specified map into this map.

This implementation iterates around the specified map and uses AbstractHashedMap.

Parameters: map the map to add

Throws: NullPointerException if the map is null

remove

public Object remove(Object key)
Removes the specified mapping from this map.

Parameters: key the mapping to remove

Returns: the value mapped to the removed key, null if key not in map

removeEntry

protected void removeEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)
Removes an entry from the chain stored in a particular index.

This implementation removes the entry from the data storage table. The size is not updated. Subclasses could override to handle changes to the map.

Parameters: entry the entry to remove hashIndex the index into the data structure previous the previous entry in the chain

removeMapping

protected void removeMapping(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)
Removes a mapping from the map.

This implementation calls removeEntry() and destroyEntry(). It also handles changes to modCount and size. Subclasses could override to fully control removals from the map.

Parameters: entry the entry to remove hashIndex the index into the data structure previous the previous entry in the chain

reuseEntry

protected void reuseEntry(AbstractHashedMap.HashEntry entry, int hashIndex, int hashCode, Object key, Object value)
Reuses an existing key-value mapping, storing completely new data.

This implementation sets all the data fields on the entry. Subclasses could populate additional entry fields.

Parameters: entry the entry to update, not null hashIndex the index in the data array hashCode the hash code of the key to add key the key to add value the value to add

size

public int size()
Gets the size of the map.

Returns: the size

toString

public String toString()
Gets the map as a String.

Returns: a string version of the map

updateEntry

protected void updateEntry(AbstractHashedMap.HashEntry entry, Object newValue)
Updates an existing key-value mapping to change the value.

This implementation calls setValue() on the entry. Subclasses could override to handle changes to the map.

Parameters: entry the entry to update newValue the new value to store

values

public Collection values()
Gets the values view of the map. Changes made to the view affect this map. To simply iterate through the values, use mapIterator.

Returns: the values view

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