org.apache.commons.collections.map

## Class AbstractLinkedMap

- java.lang.Object
- - java.util.AbstractMap
  - - org.apache.commons.collections.map.AbstractHashedMap
    - - org.apache.commons.collections.map.AbstractLinkedMap

- All Implemented Interfaces:
    Map, IterableMap, OrderedMap
  Direct Known 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
  Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
  Author:
    java util LinkedHashMap, Stephen Colebourne

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected static class` | `AbstractLinkedMap.EntrySetIterator` EntrySet iterator.
    `protected static class` | `AbstractLinkedMap.KeySetIterator` KeySet iterator.
    `protected static class` | `AbstractLinkedMap.LinkEntry` LinkEntry that stores the data.
    `protected static class` | `AbstractLinkedMap.LinkIterator` Base Iterator that iterates in link order.
    `protected static class` | `AbstractLinkedMap.LinkMapIterator` MapIterator implementation.
    `protected static class` | `AbstractLinkedMap.ValuesIterator` Values iterator.

    - ### Nested classes/interfaces inherited from class org.apache.commons.collections.map.AbstractHashedMap

      `AbstractHashedMap.EntrySet, AbstractHashedMap.HashEntry, AbstractHashedMap.HashIterator, AbstractHashedMap.HashMapIterator, AbstractHashedMap.KeySet, AbstractHashedMap.Values`

    - ### Nested classes/interfaces inherited from class java.util.AbstractMap

      `AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry`

    - ### Nested classes/interfaces inherited from interface java.util.Map

      `Map.Entry`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected AbstractLinkedMap.LinkEntry` | `header` Header in the linked list

    - ### Fields inherited from class org.apache.commons.collections.map.AbstractHashedMap

      `data, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_THRESHOLD, entrySet, GETKEY_INVALID, GETVALUE_INVALID, keySet, loadFactor, MAXIMUM_CAPACITY, modCount, NO_NEXT_ENTRY, NO_PREVIOUS_ENTRY, NULL, REMOVE_INVALID, SETVALUE_INVALID, size, threshold, values`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `AbstractLinkedMap()` Constructor only used in deserialization, do not use otherwise.
    `protected` | `AbstractLinkedMap(int initialCapacity)` Constructs a new, empty map with the specified initial capacity.
    `protected` | `AbstractLinkedMap(int initialCapacity, float loadFactor)` Constructs a new, empty map with the specified initial capacity and load factor.
    `protected` | `AbstractLinkedMap(int initialCapacity, float loadFactor, int threshold)` Constructor which performs no validation on the passed in parameters.
    `protected` | `AbstractLinkedMap(Map map)` Constructor copying elements from another map.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected 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.
    `protected AbstractHashedMap.HashEntry` | `createEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)` Creates an entry to store the data.
    `protected Iterator` | `createEntrySetIterator()` Creates an entry set iterator.
    `protected Iterator` | `createKeySetIterator()` Creates a key set iterator.
    `protected Iterator` | `createValuesIterator()` Creates a values iterator.
    `protected AbstractLinkedMap.LinkEntry` | `entryAfter(AbstractLinkedMap.LinkEntry entry)` Gets the `after` field from a `LinkEntry`.
    `protected AbstractLinkedMap.LinkEntry` | `entryBefore(AbstractLinkedMap.LinkEntry entry)` Gets the `before` field from a `LinkEntry`.
    `Object` | `firstKey()` Gets the first key in the map, which is the most recently inserted.
    `protected AbstractLinkedMap.LinkEntry` | `getEntry(int index)` Gets the key at the specified index.
    `protected 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.
    `protected void` | `removeEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)` Removes an entry from the map and the linked list.

    - ### Methods inherited from class org.apache.commons.collections.map.AbstractHashedMap

      `addMapping, calculateNewCapacity, calculateThreshold, checkCapacity, clone, containsKey, convertKey, destroyEntry, doReadObject, doWriteObject, ensureCapacity, entryHashCode, entryKey, entryNext, entrySet, entryValue, equals, get, getEntry, hash, hashCode, hashIndex, isEmpty, isEqualKey, isEqualValue, keySet, put, putAll, remove, removeMapping, reuseEntry, size, toString, updateEntry, values`

    - ### Methods inherited from class java.lang.Object

      `finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface java.util.Map

      `containsKey, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values`

- - ### Field Detail

    - #### header

          protected transient AbstractLinkedMap.LinkEntry header

      Header in the linked list

  - ### Constructor Detail

    - #### 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 < 1.0f
        `threshold` - the threshold, must be sensible

    - #### AbstractLinkedMap

          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

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

    - #### AbstractLinkedMap

          protected AbstractLinkedMap(Map map)

      Constructor copying elements from another map.
      Parameters:
        `map` - the map to copy
      Throws:
        `NullPointerException` - if the map is null

  - ### Method Detail

    - #### init

          protected void init()

      Initialise this subclass during construction.

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

      Overrides:
        `init` in class `AbstractHashedMap`

    - #### containsValue

          public boolean containsValue(Object value)

      Checks whether the map contains the specified value.
      Specified by:
        `containsValue` in interface `Map`
      Overrides:
        `containsValue` in class `AbstractHashedMap`
      Parameters:
        `value` - the value to search for
      Returns:
        true if the map contains the value

    - #### clear

          public void clear()

      Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
      Specified by:
        `clear` in interface `Map`
      Overrides:
        `clear` in class `AbstractHashedMap`

    - #### firstKey

          public Object firstKey()

      Gets the first key in the map, which is the most recently inserted.
      Specified by:
        `firstKey` in interface `OrderedMap`
      Returns:
        the most recently inserted key

    - #### lastKey

          public Object lastKey()

      Gets the last key in the map, which is the first inserted.
      Specified by:
        `lastKey` in interface `OrderedMap`
      Returns:
        the eldest key

    - #### nextKey

          public Object nextKey(Object key)

      Gets the next key in sequence.
      Specified by:
        `nextKey` in interface `OrderedMap`
      Parameters:
        `key` - the key to get after
      Returns:
        the next key

    - #### previousKey

          public Object previousKey(Object key)

      Gets the previous key in sequence.
      Specified by:
        `previousKey` in interface `OrderedMap`
      Parameters:
        `key` - the key to get before
      Returns:
        the previous 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:
        `IndexOutOfBoundsException` - if the index is invalid

    - #### 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.

      Overrides:
        `addEntry` in class `AbstractHashedMap`
      Parameters:
        `entry` - the entry to add
        `hashIndex` - the index into the data array to store at

    - #### 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.

      Overrides:
        `createEntry` in class `AbstractHashedMap`
      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

    - #### 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.

      Overrides:
        `removeEntry` in class `AbstractHashedMap`
      Parameters:
        `entry` - the entry to remove
        `hashIndex` - the index into the data structure
        `previous` - the previous entry in the chain

    - #### entryBefore

          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
      Since:
        Commons Collections 3.1

    - #### entryAfter

          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
      Since:
        Commons Collections 3.1

    - #### 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.

      Specified by:
        `mapIterator` in interface `IterableMap`
      Overrides:
        `mapIterator` in class `AbstractHashedMap`
      Returns:
        the map iterator

    - #### 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.

      Specified by:
        `orderedMapIterator` in interface `OrderedMap`
      Returns:
        the map iterator

    - #### createEntrySetIterator

          protected Iterator createEntrySetIterator()

      Creates an entry set iterator. Subclasses can override this to return iterators with different properties.
      Overrides:
        `createEntrySetIterator` in class `AbstractHashedMap`
      Returns:
        the entrySet iterator

    - #### createKeySetIterator

          protected Iterator createKeySetIterator()

      Creates a key set iterator. Subclasses can override this to return iterators with different properties.
      Overrides:
        `createKeySetIterator` in class `AbstractHashedMap`
      Returns:
        the keySet iterator

    - #### createValuesIterator

          protected Iterator createValuesIterator()

      Creates a values iterator. Subclasses can override this to return iterators with different properties.
      Overrides:
        `createValuesIterator` in class `AbstractHashedMap`
      Returns:
        the values iterator

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