org.apache.lucene.search.similarities
Class PerFieldSimilarityWrapper

java.lang.Object
  extended by org.apache.lucene.search.similarities.Similarity
      extended by org.apache.lucene.search.similarities.PerFieldSimilarityWrapper

public abstract class PerFieldSimilarityWrapper
extends Similarity

Provides the ability to use a different Similarity for different fields.

Subclasses should implement get(String) to return an appropriate Similarity (for example, using field-specific parameter values) for the field.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary
 
Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity
Similarity.SimScorer, Similarity.SimWeight
 
Constructor Summary
PerFieldSimilarityWrapper()
          Sole constructor.
 
Method Summary
 long computeNorm(FieldInvertState state)
          Computes the normalization value for a field, given the accumulated state of term processing for this field (see FieldInvertState).
 Similarity.SimWeight computeWeight(float queryBoost, CollectionStatistics collectionStats, TermStatistics... termStats)
          Compute any collection-level weight (e.g.
abstract  Similarity get(String name)
          Returns a Similarity for scoring a field.
 Similarity.SimScorer simScorer(Similarity.SimWeight weight, AtomicReaderContext context)
          Creates a new Similarity.SimScorer to score matching documents from a segment of the inverted index.
 
Methods inherited from class org.apache.lucene.search.similarities.Similarity
coord, queryNorm
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

PerFieldSimilarityWrapper

public PerFieldSimilarityWrapper()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

computeNorm

public final long computeNorm(FieldInvertState state)
Description copied from class: Similarity
Computes the normalization value for a field, given the accumulated state of term processing for this field (see FieldInvertState).

Matches in longer fields are less precise, so implementations of this method usually set smaller values when state.getLength() is large, and larger values when state.getLength() is small.

Specified by:
computeNorm in class Similarity
Parameters:
state - current processing state for this field
Returns:
computed norm value

computeWeight

public final Similarity.SimWeight computeWeight(float queryBoost,
                                                CollectionStatistics collectionStats,
                                                TermStatistics... termStats)
Description copied from class: Similarity
Compute any collection-level weight (e.g. IDF, average document length, etc) needed for scoring a query.

Specified by:
computeWeight in class Similarity
Parameters:
queryBoost - the query-time boost.
collectionStats - collection-level statistics, such as the number of tokens in the collection.
termStats - term-level statistics, such as the document frequency of a term across the collection.
Returns:
SimWeight object with the information this Similarity needs to score a query.

simScorer

public final Similarity.SimScorer simScorer(Similarity.SimWeight weight,
                                            AtomicReaderContext context)
                                     throws IOException
Description copied from class: Similarity
Creates a new Similarity.SimScorer to score matching documents from a segment of the inverted index.

Specified by:
simScorer in class Similarity
Parameters:
weight - collection information from Similarity.computeWeight(float, CollectionStatistics, TermStatistics...)
context - segment of the inverted index to be scored.
Returns:
SloppySimScorer for scoring documents across context
Throws:
IOException - if there is a low-level I/O error

get

public abstract Similarity get(String name)
Returns a Similarity for scoring a field.



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