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 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(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 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

static class	FieldComparator.ByteComparator Parses field's values as byte (using FieldCache.getBytes(org.apache.lucene.index.IndexReader, java.lang.String) 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.IndexReader, java.lang.String) and sorts by ascending value
static class	FieldComparator.FloatComparator Parses field's values as float (using FieldCache.getFloats(org.apache.lucene.index.IndexReader, java.lang.String) and sorts by ascending value
static class	FieldComparator.IntComparator Parses field's values as int (using FieldCache.getInts(org.apache.lucene.index.IndexReader, java.lang.String) and sorts by ascending value
static class	FieldComparator.LongComparator Parses field's values as long (using FieldCache.getLongs(org.apache.lucene.index.IndexReader, java.lang.String) and sorts by ascending value
static class	FieldComparator.NumericComparator<T extends Number>
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.IndexReader, java.lang.String) and sorts by ascending value
static 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

FieldComparator()

Method Summary

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.

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 void setNextReader(IndexReader reader,
                                   int docBase)
                            throws IOException

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

Parameters:

reader - current reader

docBase - 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

binarySearch

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

binarySearch

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