org.apache.lucene.search
Class TopFieldCollector

java.lang.Object
  org.apache.lucene.search.Collector
      org.apache.lucene.search.TopDocsCollector
          org.apache.lucene.search.TopFieldCollector

public abstract class TopFieldCollector
extends TopDocsCollector

A Collector that sorts by SortField using FieldComparators.

See the create(org.apache.lucene.search.Sort, int, boolean, boolean, boolean, boolean) method for instantiating a TopFieldCollector.

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

Field Summary

Fields inherited from class org.apache.lucene.search.TopDocsCollector

EMPTY_TOPDOCS, pq, totalHits

Method Summary

boolean	acceptsDocsOutOfOrder() Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).
static TopFieldCollector	create(Sort sort, int numHits, boolean fillFields, boolean trackDocScores, boolean trackMaxScore, boolean docsScoredInOrder) Creates a new TopFieldCollector from the given arguments.
protected TopDocs	newTopDocs(ScoreDoc[] results, int start) Returns a TopDocs instance containing the given results.
protected void	populateResults(ScoreDoc[] results, int howMany) Populates the results array with the ScoreDoc instaces.

Methods inherited from class org.apache.lucene.search.TopDocsCollector

getTotalHits, topDocs, topDocs, topDocs

Methods inherited from class org.apache.lucene.search.Collector

collect, setNextReader, setScorer

Methods inherited from class java.lang.Object

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

Method Detail

create

public static TopFieldCollector create(Sort sort,
                                       int numHits,
                                       boolean fillFields,
                                       boolean trackDocScores,
                                       boolean trackMaxScore,
                                       boolean docsScoredInOrder)
                                throws IOException

Creates a new TopFieldCollector from the given arguments.

NOTE: The instances returned by this method pre-allocate a full array of length numHits.

Parameters:

sort - the sort criteria (SortFields).

numHits - the number of results to collect.

fillFields - specifies whether the actual field values should be returned on the results (FieldDoc).

trackDocScores - specifies whether document scores should be tracked and set on the results. Note that if set to false, then the results' scores will be set to Float.NaN. Setting this to true affects performance, as it incurs the score computation on each competitive result. Therefore if document scores are not required by the application, it is recommended to set it to false.

trackMaxScore - specifies whether the query's maxScore should be tracked and set on the resulting TopDocs. Note that if set to false, TopDocs.getMaxScore() returns Float.NaN. Setting this to true affects performance as it incurs the score computation on each result. Also, setting this true automatically sets trackDocScores to true as well.

docsScoredInOrder - specifies whether documents are scored in doc Id order or not by the given Scorer in Collector.setScorer(Scorer).

Returns:

a TopFieldCollector instance which will sort the results by the sort criteria.

Throws:

IOException

populateResults

protected void populateResults(ScoreDoc[] results,
                               int howMany)

Description copied from class: TopDocsCollector

Populates the results array with the ScoreDoc instaces. This can be overridden in case a different ScoreDoc type should be returned.

Overrides:

populateResults in class TopDocsCollector

newTopDocs

protected TopDocs newTopDocs(ScoreDoc[] results,
                             int start)

Description copied from class: TopDocsCollector

Returns a TopDocs instance containing the given results. If results is null it means there are no results to return, either because there were 0 calls to collect() or because the arguments to topDocs were invalid.

Overrides:

newTopDocs in class TopDocsCollector

acceptsDocsOutOfOrder

public boolean acceptsDocsOutOfOrder()

Description copied from class: Collector

Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).

Most Lucene Query implementations will visit matching docIDs in order. However, some queries (currently limited to certain cases of BooleanQuery) can achieve faster searching if the Collector allows them to deliver the docIDs out of order.

Many collectors don't mind getting docIDs out of order, so it's important to return true here.

Specified by:

acceptsDocsOutOfOrder in class Collector