Package org.apache.commons.collections4.map

Class AbstractLinkedMap<K,​V>

  • Type Parameters:
    K - the type of the keys in this map
    V - the type of the values in this map
    All Implemented Interfaces:
    Map<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, OrderedMap<K,​V>, Put<K,​V>
    Direct Known Subclasses:
    LinkedMap, LRUMap
    public abstract class AbstractLinkedMap<K,​V>
extends AbstractHashedMap<K,​V>
implements OrderedMap<K,​V>
    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:
    3.0

    • 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 negative

      • 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 negative
        IllegalArgumentException - if the load factor is less than zero

      • AbstractLinkedMap

        protected AbstractLinkedMap​(Map<? extends K,​? extends V> map)
        Constructor copying elements from another map.
        Parameters:
        map - the map to copy
        Throws:
        NullPointerException - if the map is null

    • Method Detail

      • 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<K,​V>
        Specified by:
        clear in interface Put<K,​V>
        Overrides:
        clear in class AbstractHashedMap<K,​V>
        See Also:
        Map.clear()

      • firstKey

        public K firstKey()
        Gets the first key in the map, which is the first inserted.
        Specified by:
        firstKey in interface OrderedMap<K,​V>
        Returns:
        the eldest key

      • lastKey

        public K lastKey()
        Gets the last key in the map, which is the most recently inserted.
        Specified by:
        lastKey in interface OrderedMap<K,​V>
        Returns:
        the most recently inserted key

      • nextKey

        public K nextKey​(Object key)
        Gets the next key in sequence.
        Specified by:
        nextKey in interface OrderedMap<K,​V>
        Parameters:
        key - the key to get after
        Returns:
        the next key

      • getEntry

        protected AbstractLinkedMap.LinkEntry<K,​V> getEntry​(Object key)
        Description copied from class: AbstractHashedMap
        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.

        Overrides:
        getEntry in class AbstractHashedMap<K,​V>
        Parameters:
        key - the key
        Returns:
        the entry, null if no match

      • previousKey

        public K previousKey​(Object key)
        Gets the previous key in sequence.
        Specified by:
        previousKey in interface OrderedMap<K,​V>
        Parameters:
        key - the key to get before
        Returns:
        the previous key

      • addEntry

        protected void addEntry​(AbstractHashedMap.HashEntry<K,​V> 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<K,​V>
        Parameters:
        entry - the entry to add
        hashIndex - the index into the data array to store at

      • createEntry

        protected AbstractLinkedMap.LinkEntry<K,​V> createEntry​(AbstractHashedMap.HashEntry<K,​V> next,
                                                             int hashCode,
                                                             K key,
                                                             V value)
        Creates an entry to store the data.

        This implementation creates a new LinkEntry instance.

        Overrides:
        createEntry in class AbstractHashedMap<K,​V>
        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<K,​V> entry,
                           int hashIndex,
                           AbstractHashedMap.HashEntry<K,​V> 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<K,​V>
        Parameters:
        entry - the entry to remove
        hashIndex - the index into the data structure
        previous - the previous entry in the chain

      • mapIterator

        public OrderedMapIterator<K,​V> 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.

        Specified by:
        mapIterator in interface IterableGet<K,​V>
        Specified by:
        mapIterator in interface OrderedMap<K,​V>
        Overrides:
        mapIterator in class AbstractHashedMap<K,​V>
        Returns:
        the map iterator

      • createKeySetIterator

        protected Iterator<K> createKeySetIterator()
        Creates a key set iterator. Subclasses can override this to return iterators with different properties.
        Overrides:
        createKeySetIterator in class AbstractHashedMap<K,​V>
        Returns:
        the keySet iterator

      • createValuesIterator

        protected Iterator<V> createValuesIterator()
        Creates a values iterator. Subclasses can override this to return iterators with different properties.
        Overrides:
        createValuesIterator in class AbstractHashedMap<K,​V>
        Returns:
        the values iterator