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## org.apache.lucene.search
Class Scorer

    java.lang.Object
      org.apache.lucene.search.DocIdSetIterator
          org.apache.lucene.search.Scorer

Direct Known Subclasses:
  ConstantScoreQuery.ConstantScorer, ScoreCachingWrappingScorer, SpanScorer

    public abstract class Scorer

extends DocIdSetIterator

Expert: Common scoring functionality for different types of queries.

A `Scorer` iterates over documents matching a query in increasing order of doc Id.

Document scores are computed using a given `Similarity` implementation.

NOTE: The values Float.Nan, Float.NEGATIVE_INFINITY and Float.POSITIVE_INFINITY are not valid scores. Certain collectors (eg `TopScoreDocCollector`) will not properly collect hits with these scores.

Nested Class Summary
`static class` | `Scorer.ScorerVisitor<P extends Query,C extends Query,S extends Scorer>` A callback to gather information from a scorer and its sub-scorers.

Field Summary
`protected Weight` | `weight`

Fields inherited from class org.apache.lucene.search.DocIdSetIterator
`NO_MORE_DOCS`

Constructor Summary
`protected` | `Scorer(Similarity similarity)` Deprecated. Use `Scorer(Weight)` instead.
`protected` | `Scorer(Similarity similarity, Weight weight)` Deprecated. Use `Scorer(Weight)` instead.
`protected` | `Scorer(Weight weight)` Constructs a Scorer

Method Summary
`float` | `freq()` Returns number of matches for the current document.
`Similarity` | `getSimilarity()` Deprecated. Store any Similarity you might need privately in your implementation instead.
`abstract float` | `score()` Returns the score of the current document matching the query.
`void` | `score(Collector collector)` Scores and collects all matching documents.
`protected boolean` | `score(Collector collector, int max, int firstDocID)` Expert: Collects matching documents in a range.
`void` | `visitScorers(Scorer.ScorerVisitor<Query,Query,Scorer> visitor)` Expert: call this to gather details for all sub-scorers for this query.
`void` | `visitSubScorers(Query parent, BooleanClause.Occur relationship, Scorer.ScorerVisitor<Query,Query,Scorer> visitor)` `Scorer` subclasses should implement this method if the subclass itself contains multiple scorers to support gathering details for sub-scorers via `Scorer.ScorerVisitor`

Methods inherited from class org.apache.lucene.search.DocIdSetIterator
`advance, docID, nextDoc`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### weight

    protected final Weight weight

Constructor Detail

### Scorer

    protected Scorer(Weight weight)

  Constructs a Scorer

  Parameters:
    `weight` - The scorers `Weight`.

### Scorer

    @Deprecated
    protected Scorer(Similarity similarity)

  Deprecated. Use `Scorer(Weight)` instead.

  Constructs a Scorer.

  Parameters:
    `similarity` - The `Similarity` implementation used by this scorer.

### Scorer

    @Deprecated
    protected Scorer(Similarity similarity,
                                Weight weight)

  Deprecated. Use `Scorer(Weight)` instead.

  Constructs a Scorer

  Parameters:
    `similarity` - The `Similarity` implementation used by this scorer.
    `weight` - The scorers `Weight`

Method Detail

### getSimilarity

    @Deprecated
    public Similarity getSimilarity()

  Deprecated. Store any Similarity you might need privately in your implementation instead.

  Returns the Similarity implementation used by this scorer.

### score

    public void score(Collector collector)
               throws IOException

  Scores and collects all matching documents.

  Parameters:
    `collector` - The collector to which all matching documents are passed.
  Throws:
    `IOException`

### score

    protected boolean score(Collector collector,
                            int max,
                            int firstDocID)
                     throws IOException

  Expert: Collects matching documents in a range. Hook for optimization. Note, `firstDocID` is added to ensure that `DocIdSetIterator.nextDoc()` was called before this method.

  NOTE: Because of backwards compatibility, this method is still declared as protected, but it is intended to be public, because it's called from other classes (like BooleanScorer). If you subclass `Scorer`, you should declare the overridden method as public to ease transition to Lucene 4.0, where it will be public.

  Parameters:
    `collector` - The collector to which all matching documents are passed.
    `max` - Do not score documents past this.
    `firstDocID` - The first document ID (ensures `DocIdSetIterator.nextDoc()` is called before this method.
  Returns:
    true if more matching documents may remain.
  Throws:
    `IOException`

### score

    public abstract float score()
                         throws IOException

  Returns the score of the current document matching the query. Initially invalid, until `DocIdSetIterator.nextDoc()` or `DocIdSetIterator.advance(int)` is called the first time, or when called from within `Collector.collect(int)`.

  Throws:
    `IOException`

### freq

    public float freq()
               throws IOException

  Returns number of matches for the current document. This returns a float (not int) because SloppyPhraseScorer discounts its freq according to how "sloppy" the match was.

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

### visitScorers

    public void visitScorers(Scorer.ScorerVisitor<Query,Query,Scorer> visitor)

  Expert: call this to gather details for all sub-scorers for this query. This can be used, in conjunction with a custom `Collector` to gather details about how each sub-query matched the current hit.

  Parameters:
    `visitor` - a callback executed for each sub-scorer
  WARNING: This API is experimental and might change in incompatible ways in the next release.

### visitSubScorers

    public void visitSubScorers(Query parent,
                                BooleanClause.Occur relationship,
                                Scorer.ScorerVisitor<Query,Query,Scorer> visitor)

  `Scorer` subclasses should implement this method if the subclass itself contains multiple scorers to support gathering details for sub-scorers via `Scorer.ScorerVisitor`

  Note: this method will throw `UnsupportedOperationException` if no associated `Weight` instance is provided to `Scorer(Weight)`

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

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