Package org.apache.lucene.search

## Interface LeafFieldComparator

- All Known Implementing Classes:
    `DoubleComparator.DoubleLeafComparator`, `FieldComparator.RelevanceComparator`, `FieldComparator.TermValComparator`, `FloatComparator.FloatLeafComparator`, `IntComparator.IntLeafComparator`, `LongComparator.LongLeafComparator`, `NumericComparator.NumericLeafComparator`, `SimpleFieldComparator`

      public interface LeafFieldComparator

  Expert: comparator that gets instantiated on each leaf from a top-level `FieldComparator` instance.

  A leaf comparator must define these functions:

  - `setBottom(int)` This method is called by `FieldValueHitQueue` to notify the FieldComparator of the current weakest ("bottom") slot. Note that this slot may not hold the weakest value according to your comparator, in cases where your comparator is not the primary one (ie, is only used to break ties from the comparators before it).
  - `compareBottom(int)` Compare a new hit (docID) against the "weakest" (bottom) entry in the queue.
  - `compareTop(int)` Compare a new hit (docID) against the top value previously set by a call to `FieldComparator.setTopValue(T)`.
  - `copy(int, int)` Installs a new hit into the priority queue. The `FieldValueHitQueue` calls this method when a new hit is competitive.
  See Also:
    `FieldComparator`
  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Method Summary

    All Methods Instance Methods Abstract Methods Default Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `int` | `compareBottom​(int doc)` | Compare the bottom of the queue with this doc.
    `int` | `compareTop​(int doc)` | Compare the top value with this doc.
    `default DocIdSetIterator` | `competitiveIterator()` | Returns a competitive iterator
    `void` | `copy​(int slot, int doc)` | This method is called when a new hit is competitive.
    `void` | `setBottom​(int slot)` | Set the bottom slot, ie the "weakest" (sorted last) entry in the queue.
    `default void` | `setHitsThresholdReached()` | Informs this leaf comparator that hits threshold is reached.
    `void` | `setScorer​(Scorable scorer)` | Sets the Scorer to use in case a document's score is needed.

- - ### Method Detail

    - #### setBottom

          void setBottom​(int slot)
                  throws IOException

      Set the bottom slot, ie the "weakest" (sorted last) entry in the queue. When `compareBottom(int)` is called, you should compare against this slot. This will always be called before `compareBottom(int)`.
      Parameters:
        `slot` - the currently weakest (sorted last) slot in the queue
      Throws:
        `IOException`

    - #### compareBottom

          int compareBottom​(int doc)
                     throws IOException

      Compare the bottom of the queue with this doc. This will only invoked after setBottom has been called. This should return the same result as `FieldComparator.compare(int,int)`} as if bottom were slot1 and the new document were slot 2.

      For a search that hits many results, this method will be the hotspot (invoked by far the most frequently).

      Parameters:
        `doc` - that was hit
      Returns:
        any `N < 0` if the doc's value is sorted after the bottom entry (not competitive), any `N > 0` if the doc's value is sorted before the bottom entry and `0` if they are equal.
      Throws:
        `IOException`

    - #### compareTop

          int compareTop​(int doc)
                  throws IOException

      Compare the top value with this doc. This will only invoked after setTopValue has been called. This should return the same result as `FieldComparator.compare(int,int)`} as if topValue were slot1 and the new document were slot 2. This is only called for searches that use searchAfter (deep paging).
      Parameters:
        `doc` - that was hit
      Returns:
        any `N < 0` if the doc's value is sorted after the top entry (not competitive), any `N > 0` if the doc's value is sorted before the top entry and `0` if they are equal.
      Throws:
        `IOException`

    - #### copy

          void copy​(int slot,
                    int doc)
             throws IOException

      This method is called when a new hit is competitive. You should copy any state associated with this document that will be required for future comparisons, into the specified slot.
      Parameters:
        `slot` - which slot to copy the hit to
        `doc` - docID relative to current reader
      Throws:
        `IOException`

    - #### setScorer

          void setScorer​(Scorable scorer)
                  throws IOException

      Sets the Scorer to use in case a document's score is needed.
      Parameters:
        `scorer` - Scorer instance that you should use to obtain the current hit's score, if necessary.
      Throws:
        `IOException`

    - #### competitiveIterator

          default DocIdSetIterator competitiveIterator()
                                                throws IOException

      Returns a competitive iterator
      Returns:
        an iterator over competitive docs that are stronger than already collected docs or `null` if such an iterator is not available for the current comparator or segment.
      Throws:
        `IOException`

    - #### setHitsThresholdReached

          default void setHitsThresholdReached()
                                        throws IOException

      Informs this leaf comparator that hits threshold is reached. This method is called from a collector when hits threshold is reached.
      Throws:
        `IOException`