Package org.apache.lucene.search
Class FieldComparator<T>
- java.lang.Object
-
- org.apache.lucene.search.FieldComparator<T>
-
- Direct Known Subclasses:
FieldComparator.DocComparator
,FieldComparator.NumericComparator
,FieldComparator.RelevanceComparator
,FieldComparator.StringComparatorLocale
,FieldComparator.StringOrdValComparator
,FieldComparator.StringValComparator
public abstract class FieldComparator<T> extends Object
Expert: a FieldComparator compares hits so as to determine their sort order when collecting the top results withTopFieldCollector
. 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. TheFieldComparator
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 byFieldValueHitQueue
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. TheFieldValueHitQueue
calls this method when a new hit is competitive. -
setNextReader(org.apache.lucene.index.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 theFieldCache
. -
value(int)
Return the sort value stored in the specified slot. This is only called at the end of the search, in order to populateFieldDoc.fields
when returning the top results.
- WARNING: This API is experimental and might change in incompatible ways in the next release.
-
-
Nested Class Summary
Nested Classes Modifier and Type Class Description static class
FieldComparator.ByteComparator
Parses field's values as byte (usingFieldCache.getBytes(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.DocComparator
Sorts by ascending docIDstatic class
FieldComparator.DoubleComparator
Parses field's values as double (usingFieldCache.getDoubles(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.FloatComparator
Parses field's values as float (usingFieldCache.getFloats(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.IntComparator
Parses field's values as int (usingFieldCache.getInts(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.LongComparator
Parses field's values as long (usingFieldCache.getLongs(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.NumericComparator<T extends Number>
static class
FieldComparator.RelevanceComparator
Sorts by descending relevance.static class
FieldComparator.ShortComparator
Parses field's values as short (usingFieldCache.getShorts(org.apache.lucene.index.IndexReader, java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.StringComparatorLocale
Sorts by a field's value using the Collator for a given Locale.static class
FieldComparator.StringOrdValComparator
Sorts by field's natural String sort order, using ordinals.static class
FieldComparator.StringValComparator
Sorts by field's natural String sort order.
-
Constructor Summary
Constructors Constructor Description FieldComparator()
-
Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description protected static int
binarySearch(String[] a, String key)
protected static int
binarySearch(String[] a, String key, int low, int high)
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.int
compareValues(T first, T second)
Returns -1 if first is less than second.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 T
value(int slot)
Return the actual value in the slot.
-
-
-
Method Detail
-
compare
public abstract int compare(int slot1, int slot2)
Compare hit at slot1 with hit at slot2.- Parameters:
slot1
- first slot to compareslot2
- 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
-
setBottom
public abstract void setBottom(int slot)
Set the bottom slot, ie the "weakest" (sorted last) entry in the queue. WhencompareBottom(int)
is called, you should compare against this slot. This will always be called beforecompareBottom(int)
.- Parameters:
slot
- the currently weakest (sorted last) slot in the queue
-
compareBottom
public abstract int compareBottom(int doc) throws IOException
Compare the bottom of the queue with doc. This will only invoked after setBottom has been called. This should return the same result ascompare(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
-
copy
public abstract 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 todoc
- docID relative to current reader- Throws:
IOException
-
setNextReader
public abstract void setNextReader(IndexReader reader, int docBase) throws IOException
Set a new Reader. All doc correspond to the current Reader.- Parameters:
reader
- current readerdocBase
- docBase of this reader- Throws:
IOException
IOException
-
setScorer
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.
-
value
public abstract T value(int slot)
Return the actual value in the slot.- Parameters:
slot
- the value- Returns:
- value in this slot
-
compareValues
public int compareValues(T first, T second)
Returns -1 if first is less than second. Default impl to assume the type implements Comparable and invoke .compareTo; be sure to override this method if your FieldComparator's type isn't a Comparable or if your values may sometimes be null
-
-