org.apache.lucene.search.DocIdSetIterator Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.search;
import java.io.IOException;
/**
* 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
* {@link #NO_MORE_DOCS} is set to {@value #NO_MORE_DOCS} in order to be used as
* a sentinel object. Implementations of this class are expected to consider
* {@link Integer#MAX_VALUE} as an invalid value.
*/
public abstract class DocIdSetIterator {
/** An empty {@code DocIdSetIterator} instance */
public static final DocIdSetIterator empty() {
return new DocIdSetIterator() {
boolean exhausted = false;
@Override
public int advance(int target) {
assert !exhausted;
assert target >= 0;
exhausted = true;
return NO_MORE_DOCS;
}
@Override
public int docID() {
return exhausted ? NO_MORE_DOCS : -1;
}
@Override
public int nextDoc() {
assert !exhausted;
exhausted = true;
return NO_MORE_DOCS;
}
@Override
public long cost() {
return 0;
}
};
}
/** A {@link DocIdSetIterator} that matches all documents up to
* {@code maxDoc - 1}. */
public static final DocIdSetIterator all(int maxDoc) {
return new DocIdSetIterator() {
int doc = -1;
@Override
public int docID() {
return doc;
}
@Override
public int nextDoc() throws IOException {
return advance(doc + 1);
}
@Override
public int advance(int target) throws IOException {
doc = target;
if (doc >= maxDoc) {
doc = NO_MORE_DOCS;
}
return doc;
}
@Override
public long cost() {
return maxDoc;
}
};
}
/**
* When returned by {@link #nextDoc()}, {@link #advance(int)} and
* {@link #docID()} it means there are no more docs in the iterator.
*/
public static final int NO_MORE_DOCS = Integer.MAX_VALUE;
/**
* Returns the following:
*
* -1 if {@link #nextDoc()} or
* {@link #advance(int)} were not called yet.
* - {@link #NO_MORE_DOCS} if the iterator has exhausted.
*
- Otherwise it should return the doc ID it is currently on.
*
*
*
* @since 2.9
*/
public abstract int docID();
/**
* Advances to the next document in the set and returns the doc it is
* currently on, or {@link #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.
*
* @since 2.9
*/
public abstract int nextDoc() 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 {@link #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 {@link #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.
*
*
* @since 2.9
*/
public abstract int advance(int target) throws IOException;
/** Slow (linear) implementation of {@link #advance} relying on
* {@link #nextDoc()} to advance beyond the target position. */
protected final int slowAdvance(int target) throws IOException {
assert docID() < target;
int doc;
do {
doc = nextDoc();
} while (doc < target);
return doc;
}
/**
* Returns the estimated cost of this {@link 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.
*/
public abstract long cost();
}