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org.apache.commons.collections.map

Class AbstractLinkedMap

java.lang.Object
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+--org.apache.commons.collections.map.AbstractHashedMap
   |
   +--org.apache.commons.collections.map.AbstractLinkedMap

All Implemented Interfaces:
IterableMap, OrderedMap

Known Direct Subclasses:
LinkedMap, LRUMap


public class AbstractLinkedMap
extends AbstractHashedMap
implements OrderedMap

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.

Since:
Commons Collections 3.0
Authors:
java util LinkedHashMap
Stephen Colebourne

Field Summary

transient AbstractLinkedMap.LinkEntry

header

Header in the linked list

Constructor Summary

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.

Method Summary

void

addEntry(AbstractHashedMap.HashEntry entry, int hashIndex)

Adds an entry into this map, maintaining insertion order.

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.

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.

Object

firstKey()

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

AbstractLinkedMap.LinkEntry

getEntry(int index)

Gets the key at the specified index.

void

init()

Initialise this subclass during construction.

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.

void

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

Removes an entry from the map and the linked list.

Field Details

header

protected transient AbstractLinkedMap.LinkEntry header

Header in the linked list

Constructor Details

AbstractLinkedMap

protected AbstractLinkedMap()

Constructor only used in deserialization, do not use otherwise.


AbstractLinkedMap

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 <321.0f
threshold - the threshold, must be sensible

AbstractLinkedMap

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:
- if the initial capacity is less than one
- if the load factor is less than zero

AbstractLinkedMap

protected AbstractLinkedMap(int initialCapacity)

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

Parameters:
initialCapacity - the initial capacity
Throws:
- if the initial capacity is less than one

AbstractLinkedMap

protected AbstractLinkedMap(Map map)

Constructor copying elements from another map.

Parameters:
map - the map to copy
Throws:
- if the map is null

Method Details

addEntry

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

clear

public void clear()

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


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

createEntry

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

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

firstKey

public Object firstKey()

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

Returns:
the most recently inserted key

getEntry

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:
- if the index is invalid

init

protected void init()

Initialise this subclass during construction.


lastKey

public Object lastKey()

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

Returns:
the eldest key

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.

Returns:
the map iterator

nextKey

public Object nextKey(Object key)

Gets the next key in sequence.

Parameters:
key - the key to get after
Returns:
the next key

orderedMapIterator

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

previousKey

public Object previousKey(Object key)

Gets the previous key in sequence.

Parameters:
key - the key to get before
Returns:
the previous key

removeEntry

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