Module org.apache.commons.collections4
Package org.apache.commons.collections4.trie

Class PatriciaTrie<E>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.commons.collections4.trie.AbstractBitwiseTrie<K,V>
org.apache.commons.collections4.trie.PatriciaTrie<E>
Type Parameters:
E - the type of the values in this map
All Implemented Interfaces:
Serializable, Map<String,E>, SortedMap<String,E>, Get<String,E>, IterableGet<String,E>, IterableMap<String,E>, IterableSortedMap<String,E>, OrderedMap<String,E>, Put<String,E>, Trie<String,E>
public class PatriciaTrie<E> extends AbstractBitwiseTrie<K,V>
Implementation of a PATRICIA Trie (Practical Algorithm to Retrieve Information Coded in Alphanumeric).

A PATRICIA Trie is a compressed Trie. Instead of storing all data at the edges of the Trie (and having empty internal nodes), PATRICIA stores data in every node. This allows for very efficient traversal, insert, delete, predecessor, successor, prefix, range, and select(Object) operations. All operations are performed at worst in O(K) time, where K is the number of bits in the largest item in the tree. In practice, operations actually take O(A(K)) time, where A(K) is the average number of bits of all items in the tree.

Most importantly, PATRICIA requires very few comparisons to keys while doing any operation. While performing a lookup, each comparison (at most K of them, described above) will perform a single bit comparison against the given key, instead of comparing the entire key to another key.

The Trie can return operations in lexicographical order using the 'prefixMap', 'submap', or 'iterator' methods. The Trie can also scan for items that are 'bitwise' (using an XOR metric) by the 'select' method. Bitwise closeness is determined by the KeyAnalyzer returning true or false for a bit being set or not in a given key.

This PATRICIA Trie supports both variable length & fixed length keys. Some methods, such as Trie.prefixMap(Object) are suited only to variable length keys.

Since:
4.0
See Also:

  • Field Details

    • modCount

      protected transient int modCount
      The number of times this Trie has been modified. It's used to detect concurrent modifications and fail-fast the Iterators.

  • Constructor Details

  • Method Details

    • clear

      public void clear()
      Specified by:
      clear in interface Map<K,V>
      Specified by:
      clear in interface Put<K,V>
      Overrides:
      clear in class AbstractMap<K,V>
      See Also:

    • size

      public int size()
      Specified by:
      size in interface Get<K,V>
      Specified by:
      size in interface Map<K,V>
      Overrides:
      size in class AbstractMap<K,V>
      Returns:
      the number of key-value mappings in this map
      See Also:

    • put

      public E put(String key, E value)
      Description copied from interface: Put
      Note that the return type is Object, rather than V as in the Map interface. See the class Javadoc for further info.
      Specified by:
      put in interface Map<K,V>
      Specified by:
      put in interface Put<K,V>
      Overrides:
      put in class AbstractMap<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - value to be associated with the specified key
      Returns:
      the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)
      See Also:

    • get

      public E get(Object k)
      Specified by:
      get in interface Get<K,V>
      Specified by:
      get in interface Map<K,V>
      Overrides:
      get in class AbstractMap<K,V>
      Parameters:
      k - the key whose associated value is to be returned
      Returns:
      the value to which the specified key is mapped, or null if this map contains no mapping for the key
      See Also:

    • select

      public Map.Entry<String,E> select(String key)
      Returns the Map.Entry whose key is closest in a bitwise XOR metric to the given key. This is NOT lexicographic closeness. For example, given the keys:
      1. D = 1000100
      2. H = 1001000
      3. L = 1001100
      If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.
      Parameters:
      key - the key to use in the search
      Returns:
      the Map.Entry whose key is closest in a bitwise XOR metric to the provided key

    • selectKey

      public String selectKey(String key)
      Returns the key that is closest in a bitwise XOR metric to the provided key. This is NOT lexicographic closeness! For example, given the keys:
      1. D = 1000100
      2. H = 1001000
      3. L = 1001100
      If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.
      Parameters:
      key - the key to use in the search
      Returns:
      the key that is closest in a bitwise XOR metric to the provided key

    • selectValue

      public E selectValue(String key)
      Returns the value whose key is closest in a bitwise XOR metric to the provided key. This is NOT lexicographic closeness! For example, given the keys:
      1. D = 1000100
      2. H = 1001000
      3. L = 1001100
      If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.
      Parameters:
      key - the key to use in the search
      Returns:
      the value whose key is closest in a bitwise XOR metric to the provided key

    • containsKey

      public boolean containsKey(Object k)
      Specified by:
      containsKey in interface Get<K,V>
      Specified by:
      containsKey in interface Map<K,V>
      Overrides:
      containsKey in class AbstractMap<K,V>
      Parameters:
      k - key whose presence in this map is to be tested
      Returns:
      true if this map contains a mapping for the specified key
      See Also:

    • entrySet

      public Set<Map.Entry<String,E>> entrySet()
      Specified by:
      entrySet in interface Get<K,V>
      Specified by:
      entrySet in interface Map<K,V>
      Specified by:
      entrySet in interface SortedMap<K,V>
      Specified by:
      entrySet in class AbstractMap<K,V>
      Returns:
      a set view of the mappings contained in this map
      See Also:

    • keySet

      public Set<String> keySet()
      Specified by:
      keySet in interface Get<K,V>
      Specified by:
      keySet in interface Map<K,V>
      Specified by:
      keySet in interface SortedMap<K,V>
      Overrides:
      keySet in class AbstractMap<K,V>
      Returns:
      a set view of the keys contained in this map
      See Also:

    • values

      public Collection<E> values()
      Specified by:
      values in interface Get<K,V>
      Specified by:
      values in interface Map<K,V>
      Specified by:
      values in interface SortedMap<K,V>
      Overrides:
      values in class AbstractMap<K,V>
      Returns:
      a collection view of the values contained in this map
      See Also:

    • remove

      public E remove(Object k)
      Specified by:
      remove in interface Get<K,V>
      Specified by:
      remove in interface Map<K,V>
      Overrides:
      remove in class AbstractMap<K,V>
      Parameters:
      k - key whose mapping is to be removed from the map
      Returns:
      the previous value associated with key, or null if there was no mapping for key.
      Throws:
      ClassCastException - if provided key is of an incompatible type
      See Also:

    • comparator

      public Comparator<? super String> comparator()

    • firstKey

      public String firstKey()
      Description copied from interface: OrderedMap
      Gets the first key currently in this map.
      Returns:
      the first key currently in this map

    • lastKey

      public String lastKey()
      Description copied from interface: OrderedMap
      Gets the last key currently in this map.
      Returns:
      the last key currently in this map

    • nextKey

      public String nextKey(String key)
      Description copied from interface: OrderedMap
      Gets the next key after the one specified.
      Parameters:
      key - the key to search for next from
      Returns:
      the next key, null if no match or at end

    • previousKey

      public String previousKey(String key)
      Description copied from interface: OrderedMap
      Gets the previous key before the one specified.
      Parameters:
      key - the key to search for previous from
      Returns:
      the previous key, null if no match or at start

    • mapIterator

      public OrderedMapIterator<String,E> mapIterator()
      Description copied from interface: OrderedMap
      Obtains an OrderedMapIterator over the map.

      A ordered map iterator is an efficient way of iterating over maps in both directions.

      Returns:
      a map iterator

    • prefixMap

      public SortedMap<String,E> prefixMap(String key)
      Description copied from interface: Trie
      Returns a view of this Trie of all elements that are prefixed by the given key.

      In a Trie with fixed size keys, this is essentially a Map.get(Object) operation.

      For example, if the Trie contains 'Anna', 'Anael', 'Analu', 'Andreas', 'Andrea', 'Andres', and 'Anatole', then a lookup of 'And' would return 'Andreas', 'Andrea', and 'Andres'.

      Parameters:
      key - the key used in the search
      Returns:
      a SortedMap view of this Trie with all elements whose key is prefixed by the search key

    • headMap

      public SortedMap<String,E> headMap(String toKey)

    • subMap

      public SortedMap<String,E> subMap(String fromKey, String toKey)

    • tailMap

      public SortedMap<String,E> tailMap(String fromKey)