org.apache.lucene.search

## Class LongValuesSource

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

- All Implemented Interfaces:
    SegmentCacheable

      public abstract class LongValuesSource
      extends Object
      implements SegmentCacheable

  Base class for producing `LongValues` To obtain a `LongValues` object for a leaf reader, clients should call `rewrite(IndexSearcher)` against the top-level searcher, and then `getValues(LeafReaderContext, DoubleValues)`. LongValuesSource objects for long and int-valued NumericDocValues fields can be obtained by calling `fromLongField(String)` and `fromIntField(String)`. To obtain a LongValuesSource from a float or double-valued NumericDocValues field, use `DoubleValuesSource.fromFloatField(String)` or `DoubleValuesSource.fromDoubleField(String)` and then call `DoubleValuesSource.toLongValuesSource()`.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `LongValuesSource()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static LongValuesSource` | `constant(long value)` Creates a LongValuesSource that always returns a constant value
    `abstract boolean` | `equals(Object obj)`
    `static LongValuesSource` | `fromIntField(String field)` Creates a LongValuesSource that wraps an int-valued field
    `static LongValuesSource` | `fromLongField(String field)` Creates a LongValuesSource that wraps a long-valued field
    `SortField` | `getSortField(boolean reverse)` Create a sort field based on the value of this producer
    `abstract LongValues` | `getValues(LeafReaderContext ctx, DoubleValues scores)` Returns a `LongValues` 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 LongValuesSource` | `rewrite(IndexSearcher searcher)` Return a LongValuesSource specialised for the given IndexSearcher Implementations should assume that this will only be called once.
    `DoubleValuesSource` | `toDoubleValuesSource()` Convert to a DoubleValuesSource by casting long values to doubles
    `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`

- - ### Constructor Detail

    - #### LongValuesSource

          public LongValuesSource()

  - ### Method Detail

    - #### getValues

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

      Returns a `LongValues` 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

    - #### 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`

    - #### rewrite

          public abstract LongValuesSource rewrite(IndexSearcher searcher)
                                            throws IOException

      Return a LongValuesSource specialised for the given IndexSearcher Implementations should assume that this will only be called once. IndexSearcher-independent implementations can just return `this`
      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

    - #### toDoubleValuesSource

          public DoubleValuesSource toDoubleValuesSource()

      Convert to a DoubleValuesSource by casting long values to doubles

    - #### fromLongField

          public static LongValuesSource fromLongField(String field)

      Creates a LongValuesSource that wraps a long-valued field

    - #### fromIntField

          public static LongValuesSource fromIntField(String field)

      Creates a LongValuesSource that wraps an int-valued field

    - #### constant

          public static LongValuesSource constant(long value)

      Creates a LongValuesSource that always returns a constant value

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