Package org.apache.lucene.search.similarities

Class PerFieldSimilarityWrapper

java.lang.Object

org.apache.lucene.search.similarities.Similarity

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.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity

Similarity.SimScorer, Similarity.SimWeight

Constructor Summary

Constructors

Constructor	Description
PerFieldSimilarityWrapper()	Sole constructor.

Method Summary

Modifier and Type	Method	Description
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.