org.apache.lucene.search
Class FuzzyQuery

java.lang.Object
  extended by org.apache.lucene.search.Query
      extended by org.apache.lucene.search.MultiTermQuery
          extended by org.apache.lucene.search.FuzzyQuery
All Implemented Interfaces:
Serializable, Cloneable

public class FuzzyQuery
extends MultiTermQuery

Implements the fuzzy search query. The similarity measurement is based on the Levenshtein (edit distance) algorithm.

Warning: this query is not very scalable with its default prefix length of 0 - in this case, *every* term will be enumerated and cause an edit score calculation.

This query uses MultiTermQuery.TopTermsScoringBooleanQueryRewrite as default. So terms will be collected and scored according to their edit distance. Only the top terms are used for building the BooleanQuery. It is not recommended to change the rewrite mode for fuzzy queries.

See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from class org.apache.lucene.search.MultiTermQuery
MultiTermQuery.ConstantScoreAutoRewrite, MultiTermQuery.RewriteMethod, MultiTermQuery.TopTermsBoostOnlyBooleanQueryRewrite, MultiTermQuery.TopTermsScoringBooleanQueryRewrite
 
Field Summary
static int defaultMaxExpansions
           
static float defaultMinSimilarity
           
static int defaultPrefixLength
           
protected  Term term
           
 
Fields inherited from class org.apache.lucene.search.MultiTermQuery
CONSTANT_SCORE_AUTO_REWRITE_DEFAULT, CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE, CONSTANT_SCORE_FILTER_REWRITE, rewriteMethod, SCORING_BOOLEAN_QUERY_REWRITE
 
Constructor Summary
FuzzyQuery(Term term)
          Calls FuzzyQuery(term, 0.5f, 0, Integer.MAX_VALUE).
FuzzyQuery(Term term, float minimumSimilarity)
          Calls FuzzyQuery(term, minimumSimilarity, 0, Integer.MAX_VALUE).
FuzzyQuery(Term term, float minimumSimilarity, int prefixLength)
          Calls FuzzyQuery(term, minimumSimilarity, prefixLength, Integer.MAX_VALUE).
FuzzyQuery(Term term, float minimumSimilarity, int prefixLength, int maxExpansions)
          Create a new FuzzyQuery that will match terms with a similarity of at least minimumSimilarity to term.
 
Method Summary
 boolean equals(Object obj)
           
protected  FilteredTermEnum getEnum(IndexReader reader)
          Construct the enumeration to be used, expanding the pattern term.
 float getMinSimilarity()
          Returns the minimum similarity that is required for this query to match.
 int getPrefixLength()
          Returns the non-fuzzy prefix length.
 Term getTerm()
          Returns the pattern term.
 int hashCode()
           
 String toString(String field)
          Prints a query to a string, with field assumed to be the default field and omitted.
 
Methods inherited from class org.apache.lucene.search.MultiTermQuery
clearTotalNumberOfTerms, getRewriteMethod, getTotalNumberOfTerms, incTotalNumberOfTerms, rewrite, setRewriteMethod
 
Methods inherited from class org.apache.lucene.search.Query
clone, combine, createWeight, extractTerms, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, weight
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

defaultMinSimilarity

public static final float defaultMinSimilarity
See Also:
Constant Field Values

defaultPrefixLength

public static final int defaultPrefixLength
See Also:
Constant Field Values

defaultMaxExpansions

public static final int defaultMaxExpansions
See Also:
Constant Field Values

term

protected Term term
Constructor Detail

FuzzyQuery

public FuzzyQuery(Term term,
                  float minimumSimilarity,
                  int prefixLength,
                  int maxExpansions)
Create a new FuzzyQuery that will match terms with a similarity of at least minimumSimilarity to term. If a prefixLength > 0 is specified, a common prefix of that length is also required.

Parameters:
term - the term to search for
minimumSimilarity - a value between 0 and 1 to set the required similarity between the query term and the matching terms. For example, for a minimumSimilarity of 0.5 a term of the same length as the query term is considered similar to the query term if the edit distance between both terms is less than length(term)*0.5
prefixLength - length of common (non-fuzzy) prefix
maxExpansions - the maximum number of terms to match. If this number is greater than BooleanQuery.getMaxClauseCount() when the query is rewritten, then the maxClauseCount will be used instead.
Throws:
IllegalArgumentException - if minimumSimilarity is >= 1 or < 0 or if prefixLength < 0

FuzzyQuery

public FuzzyQuery(Term term,
                  float minimumSimilarity,
                  int prefixLength)
Calls FuzzyQuery(term, minimumSimilarity, prefixLength, Integer.MAX_VALUE).


FuzzyQuery

public FuzzyQuery(Term term,
                  float minimumSimilarity)
Calls FuzzyQuery(term, minimumSimilarity, 0, Integer.MAX_VALUE).


FuzzyQuery

public FuzzyQuery(Term term)
Calls FuzzyQuery(term, 0.5f, 0, Integer.MAX_VALUE).

Method Detail

getMinSimilarity

public float getMinSimilarity()
Returns the minimum similarity that is required for this query to match.

Returns:
float value between 0.0 and 1.0

getPrefixLength

public int getPrefixLength()
Returns the non-fuzzy prefix length. This is the number of characters at the start of a term that must be identical (not fuzzy) to the query term if the query is to match that term.


getEnum

protected FilteredTermEnum getEnum(IndexReader reader)
                            throws IOException
Description copied from class: MultiTermQuery
Construct the enumeration to be used, expanding the pattern term.

Specified by:
getEnum in class MultiTermQuery
Throws:
IOException

getTerm

public Term getTerm()
Returns the pattern term.


toString

public String toString(String field)
Description copied from class: Query
Prints a query to a string, with field assumed to be the default field and omitted.

The representation used is one that is supposed to be readable by QueryParser. However, there are the following limitations:

Specified by:
toString in class Query

hashCode

public int hashCode()
Overrides:
hashCode in class MultiTermQuery

equals

public boolean equals(Object obj)
Overrides:
equals in class MultiTermQuery


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