All Known Implementing Classes:

FilterLeafCollector, SimpleCollector, TopScoreDocCollector.ScorerLeafCollector
```
public interface LeafCollector
```
Collector decouples the score from the collected doc: the score computation is skipped entirely if it's not needed. Collectors that do need the score should implement the setScorer(org.apache.lucene.search.Scorable) method, to hold onto the passed Scorer instance, and call Scorable.score() within the collect method to compute the current hit's score. If your collector may request the score for a single hit multiple times, you should use ScoreCachingWrappingScorer.
NOTE: The doc that is passed to the collect method is relative to the current reader. If your collector needs to resolve this to the docID space of the Multi*Reader, you must re-base it by recording the docBase from the most recent setNextReader call. Here's a simple example showing how to collect docIDs into a BitSet:
```
 IndexSearcher searcher = new IndexSearcher(indexReader);
 final BitSet bits = new BitSet(indexReader.maxDoc());
 searcher.search(query, new Collector() {

   public LeafCollector getLeafCollector(LeafReaderContext context)
       throws IOException {
     final int docBase = context.docBase;
     return new LeafCollector() {

       // ignore scorer
       public void setScorer(Scorer scorer) throws IOException {
       }

       public void collect(int doc) throws IOException {
         bits.set(docBase + doc);
       }

     };
   }

 });
 
```
Not all collectors will need to rebase the docID. For example, a collector that simply counts the total number of hits would skip it.
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
`void`	`collect(int doc)`	Called once for every document matching a query, with the unbased document number.
`default void`	`collect(DocIdStream stream)`	Bulk-collect doc IDs.
`default DocIdSetIterator`	`competitiveIterator()`	Optionally returns an iterator over competitive documents.
`default void`	`finish()`	Hook that gets called once the leaf that is associated with this collector has finished collecting successfully, including when a `CollectionTerminatedException` is thrown.
`void`	`setScorer(Scorable scorer)`	Called before successive calls to `collect(int)`.

- Method Detail
  - setScorer
```
void setScorer(Scorable scorer)
        throws IOException
```
    Called before successive calls to collect(int). Implementations that need the score of the current document (passed-in to collect(int)), should save the passed-in Scorer and call scorer.score() when needed.
    
    Throws:
    
    IOException
  - collect
```
void collect(int doc)
      throws IOException
```
    Called once for every document matching a query, with the unbased document number.
    Note: The collection of the current segment can be terminated by throwing a CollectionTerminatedException. In this case, the last docs of the current LeafReaderContext will be skipped and IndexSearcher will swallow the exception and continue collection with the next leaf.
    Note: This is called in an inner search loop. For good search performance, implementations of this method should not call StoredFields.document(int) on every hit. Doing so can slow searches by an order of magnitude or more.
    
    Throws:
    
    IOException
  - collect
```
default void collect(DocIdStream stream)
              throws IOException
```
    Bulk-collect doc IDs.
    Note: The provided DocIdStream may be reused across calls and should be consumed immediately.
    Note: The provided DocIdStream typically only holds a small subset of query matches. This method may be called multiple times per segment.
    Like collect(int), it is guaranteed that doc IDs get collected in order, ie. doc IDs are collected in order within a DocIdStream, and if called twice, all doc IDs from the second DocIdStream will be greater than all doc IDs from the first DocIdStream.
    It is legal for callers to mix calls to collect(DocIdStream) and collect(int).
    The default implementation calls stream.forEach(this::collect).
    
    Throws:
    
    IOException
  - competitiveIterator
```
default DocIdSetIterator competitiveIterator()
                                      throws IOException
```
    Optionally returns an iterator over competitive documents.
    Collectors should delegate this method to their comparators if their comparators provide the skipping functionality over non-competitive docs.
    The default is to return null which is interpreted as the collector provide any competitive iterator.
    
    Throws:
    
    IOException
  - finish
```
default void finish()
             throws IOException
```
    Hook that gets called once the leaf that is associated with this collector has finished collecting successfully, including when a CollectionTerminatedException is thrown. This is typically useful to compile data that has been collected on this leaf, e.g. to convert facet counts on leaf ordinals to facet counts on global ordinals. The default implementation does nothing.
    Note: It can be assumed that this method will only be called once per LeafCollector instance.
    
    Throws:
    
    IOException

Interface LeafCollector

Method Summary

Method Detail

setScorer

collect

collect

competitiveIterator

finish