org.apache.lucene.search.spans

## Class Spans

- java.lang.Object
- - org.apache.lucene.search.DocIdSetIterator
  - - org.apache.lucene.search.spans.Spans

- Direct Known Subclasses:
    FilterSpans, NearSpansOrdered, NearSpansUnordered, TermSpans

      public abstract class Spans
      extends DocIdSetIterator

  Iterates through combinations of start/end positions per-doc. Each start/end position represents a range of term positions within the current document. These are enumerated in order, by increasing document number, within that by increasing start position and finally by increasing end position.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `NO_MORE_POSITIONS`

    - ### Fields inherited from class org.apache.lucene.search.DocIdSetIterator

      `NO_MORE_DOCS`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Spans()`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `TwoPhaseIterator` | `asTwoPhaseIterator()` Optional method: Return a `TwoPhaseIterator` view of this `Scorer`.
    `abstract void` | `collect(SpanCollector collector)` Collect postings data from the leaves of the current Spans.
    `protected void` | `doCurrentSpans()` Called each time the scorer's SpanScorer is advanced during frequency calculation
    `protected void` | `doStartCurrentDoc()` Called before the current doc's frequency is calculated
    `abstract int` | `endPosition()` Returns the end position for the current start position, or -1 when `nextStartPosition()` was not yet called on the current doc.
    `abstract int` | `nextStartPosition()` Returns the next start position for the current doc.
    `abstract float` | `positionsCost()` Return an estimation of the cost of using the positions of this `Spans` for any single document, but only after `asTwoPhaseIterator()` returned `null`.
    `abstract int` | `startPosition()` Returns the start position in the current doc, or -1 when `nextStartPosition()` was not yet called on the current doc.
    `String` | `toString()`
    `abstract int` | `width()` Return the width of the match, which is typically used to compute the `slop factor`.

    - ### Methods inherited from class org.apache.lucene.search.DocIdSetIterator

      `advance, all, cost, docID, empty, nextDoc, slowAdvance`

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

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

- - ### Field Detail

    - #### NO_MORE_POSITIONS

          public static final int NO_MORE_POSITIONS

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### Spans

          public Spans()

  - ### Method Detail

    - #### nextStartPosition

          public abstract int nextStartPosition()
                                         throws IOException

      Returns the next start position for the current doc. There is always at least one start/end position per doc. After the last start/end position at the current doc this returns `NO_MORE_POSITIONS`.
      Throws:
        `IOException`

    - #### startPosition

          public abstract int startPosition()

      Returns the start position in the current doc, or -1 when `nextStartPosition()` was not yet called on the current doc. After the last start/end position at the current doc this returns `NO_MORE_POSITIONS`.

    - #### endPosition

          public abstract int endPosition()

      Returns the end position for the current start position, or -1 when `nextStartPosition()` was not yet called on the current doc. After the last start/end position at the current doc this returns `NO_MORE_POSITIONS`.

    - #### width

          public abstract int width()

      Return the width of the match, which is typically used to compute the `slop factor`. It is only legal to call this method when the iterator is on a valid doc ID and positioned. The return value must be positive, and lower values means that the match is better.

    - #### collect

          public abstract void collect(SpanCollector collector)
                                throws IOException

      Collect postings data from the leaves of the current Spans. This method should only be called after `nextStartPosition()`, and before `NO_MORE_POSITIONS` has been reached.
      Parameters:
        `collector` - a SpanCollector
      Throws:
        `IOException`
      WARNING: This API is experimental and might change in incompatible ways in the next release.

    - #### positionsCost

          public abstract float positionsCost()

      Return an estimation of the cost of using the positions of this `Spans` for any single document, but only after `asTwoPhaseIterator()` returned `null`. Otherwise this method should not be called. The returned value is independent of the current document.
      WARNING: This API is experimental and might change in incompatible ways in the next release.

    - #### asTwoPhaseIterator

          public TwoPhaseIterator asTwoPhaseIterator()

      Optional method: Return a `TwoPhaseIterator` view of this `Scorer`. A return value of `null` indicates that two-phase iteration is not supported.
      See Also:
        `Scorer.twoPhaseIterator()`

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`

    - #### doStartCurrentDoc

          protected void doStartCurrentDoc()
                                    throws IOException

      Called before the current doc's frequency is calculated
      Throws:
        `IOException`

    - #### doCurrentSpans

          protected void doCurrentSpans()
                                 throws IOException

      Called each time the scorer's SpanScorer is advanced during frequency calculation
      Throws:
        `IOException`

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