org.apache.lucene.search
Class Weight

java.lang.Object
  extended by org.apache.lucene.search.Weight
All Implemented Interfaces:
Serializable
Direct Known Subclasses:
BooleanQuery.BooleanWeight, ConstantScoreQuery.ConstantWeight, DisjunctionMaxQuery.DisjunctionMaxWeight, SpanWeight

public abstract class Weight
extends Object
implements Serializable

Expert: Calculate query weights and build query scorers.

The purpose of Weight is to ensure searching does not modify a Query, so that a Query instance can be reused.
Searcher dependent state of the query should reside in the Weight.
IndexReader dependent state should reside in the Scorer.

A Weight is used in the following way:

  1. A Weight is constructed by a top-level query, given a Searcher (Query.createWeight(Searcher)).
  2. The sumOfSquaredWeights() method is called on the Weight to compute the query normalization factor Similarity.queryNorm(float) of the query clauses contained in the query.
  3. The query normalization factor is passed to normalize(float). At this point the weighting is complete.
  4. A Scorer is constructed by scorer(IndexReader,boolean,boolean).

Since:
2.9
See Also:
Serialized Form

Constructor Summary
Weight()
           
 
Method Summary
abstract  Explanation explain(IndexReader reader, int doc)
          An explanation of the score computation for the named document.
abstract  Query getQuery()
          The query that this concerns.
abstract  float getValue()
          The weight for this query.
abstract  void normalize(float norm)
          Assigns the query normalization factor to this.
abstract  Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer)
          Returns a Scorer which scores documents in/out-of order according to scoreDocsInOrder.
 boolean scoresDocsOutOfOrder()
          Returns true iff this implementation scores docs only out of order.
abstract  float sumOfSquaredWeights()
          The sum of squared weights of contained query clauses.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Weight

public Weight()
Method Detail

explain

public abstract Explanation explain(IndexReader reader,
                                    int doc)
                             throws IOException
An explanation of the score computation for the named document.

Parameters:
reader - sub-reader containing the give doc
doc -
Returns:
an Explanation for the score
Throws:
IOException

getQuery

public abstract Query getQuery()
The query that this concerns.


getValue

public abstract float getValue()
The weight for this query.


normalize

public abstract void normalize(float norm)
Assigns the query normalization factor to this.


scorer

public abstract Scorer scorer(IndexReader reader,
                              boolean scoreDocsInOrder,
                              boolean topScorer)
                       throws IOException
Returns a Scorer which scores documents in/out-of order according to scoreDocsInOrder.

NOTE: even if scoreDocsInOrder is false, it is recommended to check whether the returned Scorer indeed scores documents out of order (i.e., call scoresDocsOutOfOrder()), as some Scorer implementations will always return documents in-order.
NOTE: null can be returned if no documents will be scored by this query.

Parameters:
reader - the IndexReader for which to return the Scorer.
scoreDocsInOrder - specifies whether in-order scoring of documents is required. Note that if set to false (i.e., out-of-order scoring is required), this method can return whatever scoring mode it supports, as every in-order scorer is also an out-of-order one. However, an out-of-order scorer may not support DocIdSetIterator.nextDoc() and/or DocIdSetIterator.advance(int), therefore it is recommended to request an in-order scorer if use of these methods is required.
topScorer - if true, Scorer.score(Collector) will be called; if false, DocIdSetIterator.nextDoc() and/or DocIdSetIterator.advance(int) will be called.
Returns:
a Scorer which scores documents in/out-of order.
Throws:
IOException

sumOfSquaredWeights

public abstract float sumOfSquaredWeights()
                                   throws IOException
The sum of squared weights of contained query clauses.

Throws:
IOException

scoresDocsOutOfOrder

public boolean scoresDocsOutOfOrder()
Returns true iff this implementation scores docs only out of order. This method is used in conjunction with Collector's acceptsDocsOutOfOrder and scorer(org.apache.lucene.index.IndexReader, boolean, boolean) to create a matching Scorer instance for a given Collector, or vice versa.

NOTE: the default implementation returns false, i.e. the Scorer scores documents in-order.



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