public class

AbstractLinkedMap

extends AbstractHashedMap
implements OrderedMap
java.lang.Object
   ↳ java.util.AbstractMap<K, V>
     ↳ org.apache.commons.collections.map.AbstractHashedMap
       ↳ org.apache.commons.collections.map.AbstractLinkedMap
Known Direct Subclasses

Class Overview

An abstract implementation of a hash-based map that links entries to create an ordered map and which provides numerous points for subclasses to override.

This class implements all the features necessary for a subclass linked hash-based map. Key-value entries are stored in instances of the LinkEntry 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.

This implementation maintains order by original insertion, but subclasses may work differently. The OrderedMap interface is implemented to provide access to bidirectional iteration and extra convenience methods.

The orderedMapIterator() method provides direct access to a bidirectional iterator. The iterators from the other views can also be cast to OrderedIterator if required.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

The implementation is also designed to be subclassed, with lots of useful methods exposed.

Summary

Nested Classes
class AbstractLinkedMap.EntrySetIterator EntrySet iterator. 
class AbstractLinkedMap.KeySetIterator KeySet iterator. 
class AbstractLinkedMap.LinkEntry LinkEntry that stores the data. 
class AbstractLinkedMap.LinkIterator Base Iterator that iterates in link order. 
class AbstractLinkedMap.LinkMapIterator MapIterator implementation. 
class AbstractLinkedMap.ValuesIterator Values iterator. 
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Inherited Constants
From class org.apache.commons.collections.map.AbstractHashedMap
Fields
protected AbstractLinkedMap.LinkEntry header Header in the linked list
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Inherited Fields
From class org.apache.commons.collections.map.AbstractHashedMap
Protected Constructors
AbstractLinkedMap()
Constructor only used in deserialization, do not use otherwise.
AbstractLinkedMap(int initialCapacity, float loadFactor, int threshold)
Constructor which performs no validation on the passed in parameters.
AbstractLinkedMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity.
AbstractLinkedMap(int initialCapacity, float loadFactor)
Constructs a new, empty map with the specified initial capacity and load factor.
AbstractLinkedMap(Map map)
Constructor copying elements from another map.
Public Methods
void clear()
Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
boolean containsValue(Object value)
Checks whether the map contains the specified value.
Object firstKey()
Gets the first key in the map, which is the most recently inserted.
Object lastKey()
Gets the last key in the map, which is the first inserted.
MapIterator mapIterator()
Gets an iterator over the map.
Object nextKey(Object key)
Gets the next key in sequence.
OrderedMapIterator orderedMapIterator()
Gets a bidirectional iterator over the map.
Object previousKey(Object key)
Gets the previous key in sequence.
Protected Methods
void addEntry(AbstractHashedMap.HashEntry entry, int hashIndex)
Adds an entry into this map, maintaining insertion order.
AbstractHashedMap.HashEntry createEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)
Creates an entry to store the data.
Iterator createEntrySetIterator()
Creates an entry set iterator.
Iterator createKeySetIterator()
Creates a key set iterator.
Iterator createValuesIterator()
Creates a values iterator.
AbstractLinkedMap.LinkEntry entryAfter(AbstractLinkedMap.LinkEntry entry)
Gets the after field from a LinkEntry.
AbstractLinkedMap.LinkEntry entryBefore(AbstractLinkedMap.LinkEntry entry)
Gets the before field from a LinkEntry.
AbstractLinkedMap.LinkEntry getEntry(int index)
Gets the key at the specified index.
void init()
Initialise this subclass during construction.
void removeEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)
Removes an entry from the map and the linked list.
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Inherited Methods
From class org.apache.commons.collections.map.AbstractHashedMap
From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map
From interface org.apache.commons.collections.IterableMap
From interface org.apache.commons.collections.OrderedMap

Fields

protected AbstractLinkedMap.LinkEntry header

Header in the linked list

Protected Constructors

protected AbstractLinkedMap ()

Constructor only used in deserialization, do not use otherwise.

protected AbstractLinkedMap (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

protected AbstractLinkedMap (int initialCapacity)

Constructs a new, empty map with the specified initial capacity.

Parameters
initialCapacity the initial capacity
Throws
IllegalArgumentException if the initial capacity is less than one

protected AbstractLinkedMap (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 zero

protected AbstractLinkedMap (Map map)

Constructor copying elements from another map.

Parameters
map the map to copy
Throws
NullPointerException if the map is null

Public Methods

public void clear ()

Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.

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

public Object firstKey ()

Gets the first key in the map, which is the most recently inserted.

Returns
  • the most recently inserted key

public Object lastKey ()

Gets the last key in the map, which is the first inserted.

Returns
  • the eldest key

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.

Returns
  • the map iterator

public Object nextKey (Object key)

Gets the next key in sequence.

Parameters
key the key to get after
Returns
  • the next key

public OrderedMapIterator orderedMapIterator ()

Gets a bidirectional 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.

Returns
  • the map iterator

public Object previousKey (Object key)

Gets the previous key in sequence.

Parameters
key the key to get before
Returns
  • the previous key

Protected Methods

protected void addEntry (AbstractHashedMap.HashEntry entry, int hashIndex)

Adds an entry into this map, maintaining insertion order.

This implementation adds the entry to the data storage table and to the end of the linked list.

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

protected AbstractHashedMap.HashEntry createEntry (AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)

Creates an entry to store the data.

This implementation creates a new LinkEntry instance.

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

protected Iterator createEntrySetIterator ()

Creates an entry set iterator. Subclasses can override this to return iterators with different properties.

Returns
  • the entrySet iterator

protected Iterator createKeySetIterator ()

Creates a key set iterator. Subclasses can override this to return iterators with different properties.

Returns
  • the keySet iterator

protected Iterator createValuesIterator ()

Creates a values iterator. Subclasses can override this to return iterators with different properties.

Returns
  • the values iterator

protected AbstractLinkedMap.LinkEntry entryAfter (AbstractLinkedMap.LinkEntry entry)

Gets the after field from a LinkEntry. Used in subclasses that have no visibility of the field.

Parameters
entry the entry to query, must not be null
Returns
  • the after field of the entry
Throws
NullPointerException if the entry is null

protected AbstractLinkedMap.LinkEntry entryBefore (AbstractLinkedMap.LinkEntry entry)

Gets the before field from a LinkEntry. Used in subclasses that have no visibility of the field.

Parameters
entry the entry to query, must not be null
Returns
  • the before field of the entry
Throws
NullPointerException if the entry is null

protected AbstractLinkedMap.LinkEntry getEntry (int index)

Gets the key at the specified index.

Parameters
index the index to retrieve
Returns
  • the key at the specified index
Throws
IndexOutOfBoundsException if the index is invalid

protected void init ()

Initialise this subclass during construction.

NOTE: As from v3.2 this method calls createEntry(HashEntry, int, Object, Object) to create the map entry object.

protected void removeEntry (AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)

Removes an entry from the map and the linked list.

This implementation removes the entry from the linked list chain, then calls the superclass implementation.

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