- Direct Known Subclasses:
public abstract class FieldComparator<T> extends ObjectExpert: 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.
The document IDs passed to these methods must only move forwards, since they are using doc values iterators to retrieve sort values.
This API is designed to achieve high performance sorting, by exposing a tight interaction with
FieldValueHitQueueas 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. Segment transitions are handled by creating a dedicated per-segment
LeafFieldComparatorwhich also needs to interact with the
FieldValueHitQueuebut can optimize based on the segment to collect.
The following functions need to be implemented
compare(int, int)Compare a hit at 'slot a' with hit 'slot b'.
setTopValue(T)This method is called by
TopFieldCollectorto notify the FieldComparator of the top most value, which is used by future calls to
getLeafComparator(org.apache.lucene.index.LeafReaderContext)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 DocValues.
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.fieldswhen returning the top results.
- See Also:
- WARNING: This API is experimental and might change in incompatible ways in the next release.
Constructors Constructor Description
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description
compare(int slot1, int slot2)Compare hit at slot1 with hit at slot2.
compareValues(T first, T second)Returns a negative integer if first is less than second, 0 if they are equal and a positive integer otherwise.
disableSkipping()Informs the comparator that the skipping of documents should be disabled.
setSingleSort()Informs the comparator that sort is done on this single field.
setTopValue(T value)Record the top value, for future calls to
value(int slot)Return the actual value in the slot.
public abstract int compare(int slot1, int slot2)Compare hit at slot1 with hit at slot2.
slot1- first slot to compare
slot2- second slot to compare
N < 0if slot2's value is sorted after slot1, any
N > 0if the slot2's value is sorted before slot1 and
0if they are equal
public abstract void setTopValue(T value)
public abstract T value(int slot)Return the actual value in the slot.
slot- the value
- value in this slot
public abstract LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOExceptionGet a per-segment
LeafFieldComparatorto collect the given
LeafReaderContext. All docIDs supplied to this
LeafFieldComparatorare relative to the current reader (you must add docBase if you need to map it to a top-level docID).
context- current reader context
- the comparator to use for this segment
IOException- if there is a low-level IO error
compareValuesReturns a negative integer if first is less than second, 0 if they are equal and a positive integer otherwise. 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
public void setSingleSort()Informs the comparator that sort is done on this single field. This is useful to enable some optimizations for skipping non-competitive documents.
public void disableSkipping()Informs the comparator that the skipping of documents should be disabled. This function is called by TopFieldCollector in cases when the skipping functionality should not be applied or not necessary. An example could be when search sort is a part of the index sort, and can be already efficiently handled by TopFieldCollector, and doing extra work for skipping in the comparator is redundant.