org.apache.lucene.search.spans
Class Spans

java.lang.Object
  extended by org.apache.lucene.search.spans.Spans
Direct Known Subclasses:
NearSpansOrdered, NearSpansUnordered, SpanPositionCheckQuery.PositionCheckSpan, TermSpans

public abstract class Spans
extends Object

Expert: an enumeration of span matches. Used to implement span searching. Each span represents a range of term positions within a document. Matches are enumerated in order, by increasing document number, within that by increasing start position and finally by increasing end position.


Constructor Summary
Spans()
           
 
Method Summary
abstract  long cost()
          Returns the estimated cost of this spans.
abstract  int doc()
          Returns the document number of the current match.
abstract  int end()
          Returns the end position of the current match.
abstract  Collection<byte[]> getPayload()
          Returns the payload data for the current span.
abstract  boolean isPayloadAvailable()
          Checks if a payload can be loaded at this position.
abstract  boolean next()
          Move to the next match, returning true iff any such exists.
abstract  boolean skipTo(int target)
          Skips to the first match beyond the current, whose document number is greater than or equal to target.
abstract  int start()
          Returns the start position of the current match.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Spans

public Spans()
Method Detail

next

public abstract boolean next()
                      throws IOException
Move to the next match, returning true iff any such exists.

Throws:
IOException

skipTo

public abstract boolean skipTo(int target)
                        throws IOException
Skips to the first match beyond the current, whose document number is greater than or equal to target.

The behavior of this method is undefined when called with target ≤ current, or after the iterator has exhausted. Both cases may result in unpredicted behavior.

Returns true iff there is such a match.

Behaves as if written:

   boolean skipTo(int target) {
     do {
       if (!next())
         return false;
     } while (target > doc());
     return true;
   }
 
Most implementations are considerably more efficient than that.

Throws:
IOException

doc

public abstract int doc()
Returns the document number of the current match. Initially invalid.


start

public abstract int start()
Returns the start position of the current match. Initially invalid.


end

public abstract int end()
Returns the end position of the current match. Initially invalid.


getPayload

public abstract Collection<byte[]> getPayload()
                                       throws IOException
Returns the payload data for the current span. This is invalid until next() is called for the first time. This method must not be called more than once after each call of next(). However, most payloads are loaded lazily, so if the payload data for the current position is not needed, this method may not be called at all for performance reasons. An ordered SpanQuery does not lazy load, so if you have payloads in your index and you do not want ordered SpanNearQuerys to collect payloads, you can disable collection with a constructor option.

Note that the return type is a collection, thus the ordering should not be relied upon.

Returns:
a List of byte arrays containing the data of this payload, otherwise null if isPayloadAvailable is false
Throws:
IOException - if there is a low-level I/O error
WARNING: This API is experimental and might change in incompatible ways in the next release.

isPayloadAvailable

public abstract boolean isPayloadAvailable()
                                    throws IOException
Checks if a payload can be loaded at this position.

Payloads can only be loaded once per call to next().

Returns:
true if there is a payload available at this position that can be loaded
Throws:
IOException

cost

public abstract long cost()
Returns the estimated cost of this spans.

This is generally an upper bound of the number of documents this iterator might match, but may be a rough heuristic, hardcoded value, or otherwise completely inaccurate.



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