org.apache.lucene.search

## Class DoubleValuesSource

- java.lang.Object
- - org.apache.lucene.search.DoubleValuesSource

- All Implemented Interfaces:
    SegmentCacheable

      public abstract class DoubleValuesSource
      extends Object
      implements SegmentCacheable

  Base class for producing `DoubleValues` To obtain a `DoubleValues` object for a leaf reader, clients should call `rewrite(IndexSearcher)` against the top-level searcher, and then call `getValues(LeafReaderContext, DoubleValues)` on the resulting DoubleValuesSource. DoubleValuesSource objects for NumericDocValues fields can be obtained by calling `fromDoubleField(String)`, `fromFloatField(String)`, `fromIntField(String)` or `fromLongField(String)`, or from `fromField(String, LongToDoubleFunction)` if special long-to-double encoding is required. Scores may be used as a source for value calculations by wrapping a `Scorer` using `fromScorer(Scorer)` and passing the resulting DoubleValues to `getValues(LeafReaderContext, DoubleValues)`. The scores can then be accessed using the `SCORES` DoubleValuesSource.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static DoubleValuesSource` | `SCORES` A DoubleValuesSource that exposes a document's score If this source is used as part of a values calculation, then callers must not pass `null` as the `DoubleValues` parameter on `getValues(LeafReaderContext, DoubleValues)`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DoubleValuesSource()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static DoubleValuesSource` | `constant(double value)` Creates a DoubleValuesSource that always returns a constant value
    `abstract boolean` | `equals(Object obj)`
    `Explanation` | `explain(LeafReaderContext ctx, int docId, Explanation scoreExplanation)` An explanation of the value for the named document.
    `static DoubleValuesSource` | `fromDoubleField(String field)` Creates a DoubleValuesSource that wraps a double-valued field
    `static DoubleValuesSource` | `fromField(String field, LongToDoubleFunction decoder)` Creates a DoubleValuesSource that wraps a generic NumericDocValues field
    `static DoubleValuesSource` | `fromFloatField(String field)` Creates a DoubleValuesSource that wraps a float-valued field
    `static DoubleValuesSource` | `fromIntField(String field)` Creates a DoubleValuesSource that wraps an int-valued field
    `static DoubleValuesSource` | `fromLongField(String field)` Creates a DoubleValuesSource that wraps a long-valued field
    `static DoubleValuesSource` | `fromQuery(Query query)` Create a DoubleValuesSource that returns the score of a particular query
    `static DoubleValues` | `fromScorer(Scorer scorer)` Returns a DoubleValues instance that wraps scores returned by a Scorer
    `SortField` | `getSortField(boolean reverse)` Create a sort field based on the value of this producer
    `abstract DoubleValues` | `getValues(LeafReaderContext ctx, DoubleValues scores)` Returns a `DoubleValues` instance for the passed-in LeafReaderContext and scores If scores are not needed to calculate the values (ie `returns false`, callers may safely pass `null` for the `scores` parameter.
    `abstract int` | `hashCode()`
    `abstract boolean` | `needsScores()` Return true if document scores are needed to calculate values
    `abstract DoubleValuesSource` | `rewrite(IndexSearcher reader)` Return a DoubleValuesSource specialised for the given IndexSearcher Implementations should assume that this will only be called once.
    `LongValuesSource` | `toLongValuesSource()` Convert to a LongValuesSource by casting the double values to longs
    `abstract String` | `toString()`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface org.apache.lucene.search.SegmentCacheable

      `isCacheable`

- - ### Field Detail

    - #### SCORES

          public static final DoubleValuesSource SCORES

      A DoubleValuesSource that exposes a document's score If this source is used as part of a values calculation, then callers must not pass `null` as the `DoubleValues` parameter on `getValues(LeafReaderContext, DoubleValues)`

  - ### Constructor Detail

    - #### DoubleValuesSource

          public DoubleValuesSource()

  - ### Method Detail

    - #### getValues

          public abstract DoubleValues getValues(LeafReaderContext ctx,
                                                 DoubleValues scores)
                                          throws IOException

      Returns a `DoubleValues` instance for the passed-in LeafReaderContext and scores If scores are not needed to calculate the values (ie `returns false`, callers may safely pass `null` for the `scores` parameter.
      Throws:
        `IOException`

    - #### needsScores

          public abstract boolean needsScores()

      Return true if document scores are needed to calculate values

    - #### explain

          public Explanation explain(LeafReaderContext ctx,
                                     int docId,
                                     Explanation scoreExplanation)
                              throws IOException

      An explanation of the value for the named document.
      Parameters:
        `ctx` - the readers context to create the `Explanation` for.
        `docId` - the document's id relative to the given context's reader
      Returns:
        an Explanation for the value
      Throws:
        `IOException` - if an `IOException` occurs

    - #### rewrite

          public abstract DoubleValuesSource rewrite(IndexSearcher reader)
                                              throws IOException

      Return a DoubleValuesSource specialised for the given IndexSearcher Implementations should assume that this will only be called once. IndexReader-independent implementations can just return `this` Queries that use DoubleValuesSource objects should call rewrite() during `Query.createWeight(IndexSearcher, boolean, float)` rather than during `Query.rewrite(IndexReader)` to avoid IndexReader reference leakage For the same reason, implementations that cache references to the IndexSearcher should return a new object from this method.
      Throws:
        `IOException`

    - #### getSortField

          public SortField getSortField(boolean reverse)

      Create a sort field based on the value of this producer
      Parameters:
        `reverse` - true if the sort should be decreasing

    - #### hashCode

          public abstract int hashCode()

      Overrides:
        `hashCode` in class `Object`

    - #### equals

          public abstract boolean equals(Object obj)

      Overrides:
        `equals` in class `Object`

    - #### toString

          public abstract String toString()

      Overrides:
        `toString` in class `Object`

    - #### toLongValuesSource

          public final LongValuesSource toLongValuesSource()

      Convert to a LongValuesSource by casting the double values to longs

    - #### fromField

          public static DoubleValuesSource fromField(String field,
                                                     LongToDoubleFunction decoder)

      Creates a DoubleValuesSource that wraps a generic NumericDocValues field
      Parameters:
        `field` - the field to wrap, must have NumericDocValues
        `decoder` - a function to convert the long-valued doc values to doubles

    - #### fromDoubleField

          public static DoubleValuesSource fromDoubleField(String field)

      Creates a DoubleValuesSource that wraps a double-valued field

    - #### fromFloatField

          public static DoubleValuesSource fromFloatField(String field)

      Creates a DoubleValuesSource that wraps a float-valued field

    - #### fromLongField

          public static DoubleValuesSource fromLongField(String field)

      Creates a DoubleValuesSource that wraps a long-valued field

    - #### fromIntField

          public static DoubleValuesSource fromIntField(String field)

      Creates a DoubleValuesSource that wraps an int-valued field

    - #### constant

          public static DoubleValuesSource constant(double value)

      Creates a DoubleValuesSource that always returns a constant value

    - #### fromScorer

          public static DoubleValues fromScorer(Scorer scorer)

      Returns a DoubleValues instance that wraps scores returned by a Scorer

    - #### fromQuery

          public static DoubleValuesSource fromQuery(Query query)

      Create a DoubleValuesSource that returns the score of a particular query

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