Package org.apache.lucene.search

Class DocIdSetIterator

java.lang.Object

org.apache.lucene.search.DocIdSetIterator

Direct Known Subclasses:

DocsEnum, FilteredDocIdSetIterator, FixedBitSet.FixedBitSetIterator, OpenBitSetIterator

public abstract class DocIdSetIterator
extends Object

This abstract class defines methods to iterate over a set of non-decreasing doc ids. Note that this class assumes it iterates on doc Ids, and therefore NO_MORE_DOCS is set to 2147483647 in order to be used as a sentinel object. Implementations of this class are expected to consider Integer.MAX_VALUE as an invalid value.

Field Summary

Fields

Modifier and Type	Field	Description
static int	NO_MORE_DOCS	When returned by nextDoc(), advance(int) and docID() it means there are no more docs in the iterator.

Constructor Summary

Constructors

Constructor	Description
DocIdSetIterator()

Method Summary

Modifier and Type	Method	Description
abstract int	advance(int target)	Advances to the first beyond the current whose document number is greater than or equal to target, and returns the document number itself.
abstract long	cost()	Returns the estimated cost of this DocIdSetIterator.
abstract int	docID()	Returns the following: -1 or NO_MORE_DOCS if nextDoc() or advance(int) were not called yet.
static DocIdSetIterator	empty()	An empty DocIdSetIterator instance
abstract int	nextDoc()	Advances to the next document in the set and returns the doc it is currently on, or NO_MORE_DOCS if there are no more docs in the set. NOTE: after the iterator has exhausted you should not call this method, as it may result in unpredicted behavior.
protected int	slowAdvance(int target)	Slow (linear) implementation of advance(int) relying on nextDoc() to advance beyond the target position.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NO_MORE_DOCS

public static final int NO_MORE_DOCS

When returned by nextDoc(), advance(int) and docID() it means there are no more docs in the iterator.

See Also:

Constant Field Values

Constructor Detail

DocIdSetIterator

public DocIdSetIterator()

Method Detail

empty

public static final DocIdSetIterator empty()

An empty DocIdSetIterator instance

docID

public abstract int docID()

Returns the following:

• -1 or NO_MORE_DOCS if nextDoc() or advance(int) were not called yet.
• NO_MORE_DOCS if the iterator has exhausted.
• Otherwise it should return the doc ID it is currently on.

Since:

2.9

nextDoc

public abstract int nextDoc()
                     throws IOException

Advances to the next document in the set and returns the doc it is currently on, or NO_MORE_DOCS if there are no more docs in the set.
NOTE: after the iterator has exhausted you should not call this method, as it may result in unpredicted behavior.

Throws:

IOException

Since:

2.9

advance

public abstract int advance(int target)
                     throws IOException

Advances to the first beyond the current whose document number is greater than or equal to target, and returns the document number itself. Exhausts the iterator and returns NO_MORE_DOCS if target is greater than the highest document number in the set.

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.

When target > current it behaves as if written:

 int advance(int target) {
   int doc;
   while ((doc = nextDoc()) < target) {
   }
   return doc;
 }
 

Some implementations are considerably more efficient than that.

NOTE: this method may be called with NO_MORE_DOCS for efficiency by some Scorers. If your implementation cannot efficiently determine that it should exhaust, it is recommended that you check for that value in each call to this method.

Throws:

IOException

Since:

2.9

slowAdvance

protected final int slowAdvance(int target)
                         throws IOException

Slow (linear) implementation of advance(int) relying on nextDoc() to advance beyond the target position.

Throws:

IOException

cost

public abstract long cost()

Returns the estimated cost of this DocIdSetIterator.

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.