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

Nested Classes
Modifier and Type	Class	Description
`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

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.

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)
```

Class FieldComparator<T>

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

FieldComparator

Method Detail

compare

setBottom

compareBottom

copy

setNextReader

setScorer

value

compareValues

binarySearch

binarySearch