org.apache.lucene.search

Class FieldComparator<T>

java.lang.Object

org.apache.lucene.search.FieldComparator<T>

Direct Known Subclasses:

FieldComparator.DocComparator, FieldComparator.FloatDocValuesComparator, FieldComparator.IntDocValuesComparator, FieldComparator.NumericComparator, FieldComparator.RelevanceComparator, FieldComparator.TermOrdValComparator, FieldComparator.TermOrdValDocValuesComparator, FieldComparator.TermValComparator, FieldComparator.TermValDocValuesComparator

public abstract class FieldComparator<T>
extends Object

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(AtomicReaderContext) 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 FieldDoc.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 and Description
static class	FieldComparator.ByteComparator Parses field's values as byte (using FieldCache.getBytes(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.DocComparator Sorts by ascending docID
static class	FieldComparator.DoubleComparator Parses field's values as double (using FieldCache.getDoubles(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.FloatComparator Parses field's values as float (using FieldCache.getFloats(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.FloatDocValuesComparator Uses float index values to sort by ascending value
static class	FieldComparator.IntComparator Parses field's values as int (using FieldCache.getInts(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.IntDocValuesComparator Loads int index values and sorts by ascending value.
static class	FieldComparator.LongComparator Parses field's values as long (using FieldCache.getLongs(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.NumericComparator<T extends Number> Base FieldComparator class for numeric types
static class	FieldComparator.RelevanceComparator Sorts by descending relevance.
static class	FieldComparator.ShortComparator Parses field's values as short (using FieldCache.getShorts(org.apache.lucene.index.AtomicReader, java.lang.String, boolean) and sorts by ascending value
static class	FieldComparator.TermOrdValComparator Sorts by field's natural Term sort order, using ordinals.
static class	FieldComparator.TermOrdValDocValuesComparator Sorts by field's natural Term sort order, using ordinals; this is just like FieldComparator.TermValComparator except it uses DocValues to retrieve the sort ords saved during indexing.
static class	FieldComparator.TermValComparator Sorts by field's natural Term sort order.
static class	FieldComparator.TermValDocValuesComparator Sorts by field's natural Term sort order.

Constructor Summary

Constructors

Constructor and Description
FieldComparator()

Method Summary

Methods

Modifier and Type	Method and Description
protected static int	binarySearch(BytesRef br, FieldCache.DocTermsIndex a, BytesRef key)
protected static int	binarySearch(BytesRef br, FieldCache.DocTermsIndex a, BytesRef 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.
abstract int	compareDocToValue(int doc, T value) Returns negative result if the doc's value is less than the provided value.
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 FieldComparator<T>	setNextReader(AtomicReaderContext context) Set a new AtomicReaderContext.
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.

Methods inherited from class java.lang.Object

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

Constructor Detail

FieldComparator

public FieldComparator()

Method Detail

compare

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

setBottom

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

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 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

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 to

doc - docID relative to current reader

Throws:

IOException

setNextReader

public abstract FieldComparator<T> setNextReader(AtomicReaderContext context)
                                          throws IOException

Set a new AtomicReaderContext. All subsequent docIDs are relative to the current reader (you must add docBase if you need to map it to a top-level docID).

Parameters:

context - current reader context

Returns:

the comparator to use for this segment; most comparators can just return "this" to reuse the same comparator across segments

Throws:

IOException - if there is a low-level IO error

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

compareDocToValue

public abstract int compareDocToValue(int doc,
                    T value)
                               throws IOException

Returns negative result if the doc's value is less than the provided value.

Throws:

IOException

binarySearch

protected static final int binarySearch(BytesRef br,
               FieldCache.DocTermsIndex a,
               BytesRef key)

binarySearch

protected static final int binarySearch(BytesRef br,
               FieldCache.DocTermsIndex a,
               BytesRef key,
               int low,
               int high)