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

java.lang.Object
  extended by org.apache.lucene.search.FieldComparator<T>
Direct Known Subclasses:
FieldComparator.DocComparator, FieldComparator.NumericComparator, FieldComparator.RelevanceComparator, FieldComparator.TermOrdValComparator, FieldComparator.TermValComparator

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:

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary
static class FieldComparator.ByteComparator
          Deprecated. 
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.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.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
          Deprecated. 
static class FieldComparator.TermOrdValComparator
          Sorts by field's natural Term sort order, using ordinals.
static class FieldComparator.TermValComparator
          Sorts by field's natural Term sort order.
 
Constructor Summary
FieldComparator()
           
 
Method Summary
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


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