public abstract class

FieldComparator

extends Object
java.lang.Object
   ↳ org.apache.lucene.search.FieldComparator
Known Direct Subclasses

Class Overview

Expert: a FieldComparator compares hits so as to determine their sort order when collecting the top results with TopFieldCollector. The concrete public FieldComparator classes here correspond to the SortField types.

This API is designed to achieve high performance sorting, by exposing a tight interaction with FieldValueHitQueue as it visits hits. Whenever a hit is competitive, it's enrolled into a virtual slot, which is an int ranging from 0 to numHits-1. The FieldComparator is made aware of segment transitions during searching in case any internal state it's tracking needs to be recomputed during these transitions.

A comparator must define these functions:

  • compare(int, int) Compare a hit at 'slot a' with hit 'slot b'.
  • 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.
  • copy(int, int) Installs a new hit into the priority queue. The FieldValueHitQueue calls this method when a new hit is competitive.
  • setNextReader(IndexReader, int) Invoked when the search is switching to the next segment. You may need to update internal state of the comparator, for example retrieving new values from the FieldCache.
  • value(int) Return the sort value stored in the specified slot. This is only called at the end of the search, in order to populate fields when returning the top results.
NOTE: This API is experimental and might change in incompatible ways in the next release.

Summary

Nested Classes
class FieldComparator.ByteComparator Parses field's values as byte (using getBytes(IndexReader, String) and sorts by ascending value  
class FieldComparator.DocComparator Sorts by ascending docID  
class FieldComparator.DoubleComparator Parses field's values as double (using getDoubles(IndexReader, String) and sorts by ascending value  
class FieldComparator.FloatComparator Parses field's values as float (using getFloats(IndexReader, String) and sorts by ascending value  
class FieldComparator.IntComparator Parses field's values as int (using getInts(IndexReader, String) and sorts by ascending value  
class FieldComparator.LongComparator Parses field's values as long (using getLongs(IndexReader, String) and sorts by ascending value  
class FieldComparator.RelevanceComparator Sorts by descending relevance. 
class FieldComparator.ShortComparator Parses field's values as short (using getShorts(IndexReader, String) and sorts by ascending value  
class FieldComparator.StringComparatorLocale Sorts by a field's value using the Collator for a given Locale. 
class FieldComparator.StringOrdValComparator Sorts by field's natural String sort order, using ordinals. 
class FieldComparator.StringValComparator Sorts by field's natural String sort order. 
Public Constructors
FieldComparator()
Public Methods
abstract int compare(int slot1, int slot2)
Compare hit at slot1 with hit at slot2.
abstract int compareBottom(int doc)
Compare the bottom of the queue with doc.
abstract void copy(int slot, int doc)
This method is called when a new hit is competitive.
abstract void setBottom(int slot)
Set the bottom slot, ie the "weakest" (sorted last) entry in the queue.
abstract void setNextReader(IndexReader reader, int docBase)
Set a new Reader.
void setScorer(Scorer scorer)
Sets the Scorer to use in case a document's score is needed.
abstract Comparable value(int slot)
Return the actual value in the slot.
Protected Methods
final static int binarySearch(String[] a, String key, int low, int high)
final static int binarySearch(String[] a, String key)
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public FieldComparator ()

Public Methods

public abstract int compare (int slot1, int slot2)

Compare hit at slot1 with hit at slot2.

Parameters
slot1 first slot to compare
slot2 second slot to compare
Returns
  • any N < 0 if slot2's value is sorted after slot1, any N > 0 if the slot2's value is sorted before slot1 and 0 if they are equal

public abstract int compareBottom (int doc)

Compare the bottom of the queue with doc. This will only invoked after setBottom has been called. This should return the same result as 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

public abstract void copy (int slot, int doc)

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

public abstract void setBottom (int slot)

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

public abstract void setNextReader (IndexReader reader, int docBase)

Set a new Reader. All doc correspond to the current Reader.

Parameters
reader current reader
docBase docBase of this reader
Throws
IOException
IOException

public void setScorer (Scorer scorer)

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.

public abstract Comparable value (int slot)

Return the actual value in the slot.

Parameters
slot the value
Returns
  • value in this slot upgraded to Comparable

Protected Methods

protected static final int binarySearch (String[] a, String key, int low, int high)

protected static final int binarySearch (String[] a, String key)