org.apache.lucene.search

Class Scorer

Known Direct Subclasses:
ConstantScoreQuery.ConstantScorer, DisjunctionSumScorer, ReqExclScorer, ReqOptSumScorer

public abstract class Scorer
extends Object

Expert: Common scoring functionality for different types of queries.
A Scorer either iterates over documents matching a query, or provides an explanation of the score for a query for a given document.
Document scores are computed using a given Similarity implementation.

Constructor Summary

Scorer(Similarity similarity)
Constructs a Scorer.

Method Summary

abstract int
doc()
Returns the current document number matching the query.
abstract Explanation
explain(int doc)
Returns an explanation of the score for a document.
Similarity
getSimilarity()
Returns the Similarity implementation used by this scorer.
abstract boolean
next()
Advances to the next document matching the query.
abstract float
score()
Returns the score of the current document matching the query.
void
score(HitCollector hc)
Scores and collects all matching documents.
protected boolean
score(HitCollector hc, int max)
Expert: Collects matching documents in a range.
abstract boolean
skipTo(int target)
Skips to the first match beyond the current whose document number is greater than or equal to a given target.

Constructor Details

Scorer

protected Scorer(Similarity similarity)
Constructs a Scorer.
Parameters:
similarity - The Similarity implementation used by this scorer.

Method Details

doc

public abstract int doc()

explain

public abstract Explanation explain(int doc)
            throws IOException
Returns an explanation of the score for a document.
When this method is used, the next(), skipTo(int) and score(HitCollector) methods should not be used.
Parameters:
doc - The document number for the explanation.

getSimilarity

public Similarity getSimilarity()
Returns the Similarity implementation used by this scorer.

next

public abstract boolean next()
            throws IOException
Advances to the next document matching the query.

score

public abstract float score()
            throws IOException

score

public void score(HitCollector hc)
            throws IOException
Scores and collects all matching documents.
Parameters:
hc - The collector to which all matching documents are passed through HitCollector.collect(int,float).
When this method is used the explain(int) method should not be used.

score

protected boolean score(HitCollector hc,
                        int max)
            throws IOException
Expert: Collects matching documents in a range. Hook for optimization. Note that next() must be called once before this method is called for the first time.
Parameters:
hc - The collector to which all matching documents are passed through HitCollector.collect(int,float).
max - Do not score documents past this.
Returns:
true if more matching documents may remain.

skipTo

public abstract boolean skipTo(int target)
            throws IOException
Parameters:
target - The target document number.
Returns:
true iff there is such a match.

Behaves as if written:

boolean skipTo(int target) {
do {
if (!next())
return false;
} while (target > doc());
return true;
}
Most implementations are considerably more efficient than that.

Copyright © 2000-2007 Apache Software Foundation. All Rights Reserved.