Package org.apache.commons.text.similarity

# Class LevenshteinDistance

java.lang.Object
org.apache.commons.text.similarity.LevenshteinDistance

All Implemented Interfaces:
  `EditDistance<Integer>`, `SimilarityScore<Integer>`

public class LevenshteinDistance extends Object implements EditDistance<Integer>
An algorithm for measuring the difference between two character sequences.

This is the number of changes needed to change one sequence into another, where each change is a single character modification (deletion, insertion or substitution).

This code has been adapted from Apache Commons Lang 3.3.

Since:
  1.0

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `LevenshteinDistance()`
  This returns the default instance that uses a version of the algorithm that does not use a threshold parameter.
  `LevenshteinDistance(Integer threshold)`
  If the threshold is not null, distance calculations will be limited to a maximum length.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Integer`
  `apply(CharSequence left, CharSequence right)`
  Finds the Levenshtein distance between two Strings.
  `static LevenshteinDistance`
  `getDefaultInstance()`
  Gets the default instance.
  `Integer`
  `getThreshold()`
  Gets the distance threshold.

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

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### LevenshteinDistance

    public LevenshteinDistance()
    This returns the default instance that uses a version of the algorithm that does not use a threshold parameter.
    See Also:
      - `getDefaultInstance()`

  - ### LevenshteinDistance

    public LevenshteinDistance(Integer threshold)
    If the threshold is not null, distance calculations will be limited to a maximum length. If the threshold is null, the unlimited version of the algorithm will be used.
    Parameters:
      `threshold` - If this is null then distances calculations will not be limited. This may not be negative.

- ## Method Details

  - ### getDefaultInstance

    public static LevenshteinDistance getDefaultInstance()
    Gets the default instance.
    Returns:
      The default instance

  - ### apply

    public Integer apply(CharSequence left, CharSequence right)
    Finds the Levenshtein distance between two Strings.

    A higher score indicates a greater distance.

    The previous implementation of the Levenshtein distance algorithm was from http://www.merriampark.com/ld.htm

    Chas Emerick has written an implementation in Java, which avoids an OutOfMemoryError which can occur when my Java implementation is used with very large strings.
    This implementation of the Levenshtein distance algorithm is from http://www.merriampark.com/ldjava.htm

         distance.apply(null, *)             = IllegalArgumentException
         distance.apply(*, null)             = IllegalArgumentException
         distance.apply("","")               = 0
         distance.apply("","a")              = 1
         distance.apply("aaapppp", "")       = 7
         distance.apply("frog", "fog")       = 1
         distance.apply("fly", "ant")        = 3
         distance.apply("elephant", "hippo") = 7
         distance.apply("hippo", "elephant") = 7
         distance.apply("hippo", "zzzzzzzz") = 8
         distance.apply("hello", "hallo")    = 1

    Specified by:
      `apply` in interface `EditDistance<Integer>`
    Specified by:
      `apply` in interface `SimilarityScore<Integer>`
    Parameters:
      `left` - the first string, must not be null
      `right` - the second string, must not be null
    Returns:
      result distance, or -1
    Throws:
      `IllegalArgumentException` - if either String input `null`

  - ### getThreshold

    public Integer getThreshold()
    Gets the distance threshold.
    Returns:
      The distance threshold