org.apache.lucene.search.Scorer Maven / Gradle / Ivy
package org.apache.lucene.search;
/*
* 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.
*/
import java.io.IOException;
import java.util.Collection;
import java.util.Collections;
/**
* Expert: Common scoring functionality for different types of queries.
*
*
* A Scorer iterates over documents matching a
* query in increasing order of doc Id.
*
*
* Document scores are computed using a given Similarity
* implementation.
*
*
* NOTE: The values Float.Nan,
* Float.NEGATIVE_INFINITY and Float.POSITIVE_INFINITY are
* not valid scores. Certain collectors (eg {@link
* TopScoreDocCollector}) will not properly collect hits
* with these scores.
*/
public abstract class Scorer extends DocIdSetIterator {
/** the Scorer's parent Weight. in some cases this may be null */
// TODO can we clean this up?
protected final Weight weight;
/**
* Constructs a Scorer
* @param weight The scorers Weight.
*/
protected Scorer(Weight weight) {
this.weight = weight;
}
/** Returns the score of the current document matching the query.
* Initially invalid, until {@link #nextDoc()} or {@link #advance(int)}
* is called the first time, or when called from within
* {@link LeafCollector#collect}.
*/
public abstract float score() throws IOException;
/** Returns the freq of this Scorer on the current document */
public abstract int freq() throws IOException;
/** returns parent Weight
* @lucene.experimental
*/
public Weight getWeight() {
return weight;
}
/** Returns child sub-scorers
* @lucene.experimental */
public Collection getChildren() {
return Collections.emptyList();
}
/** A child Scorer and its relationship to its parent.
* the meaning of the relationship depends upon the parent query.
* @lucene.experimental */
public static class ChildScorer {
/**
* Child Scorer. (note this is typically a direct child, and may
* itself also have children).
*/
public final Scorer child;
/**
* An arbitrary string relating this scorer to the parent.
*/
public final String relationship;
/**
* Creates a new ChildScorer node with the specified relationship.
*
* The relationship can be any be any string that makes sense to
* the parent Scorer.
*/
public ChildScorer(Scorer child, String relationship) {
this.child = child;
this.relationship = relationship;
}
}
/**
* Optional method: Return a {@link TwoPhaseIterator} view of this
* {@link Scorer}. A return value of {@code null} indicates that
* two-phase iteration is not supported.
*
* Note that the returned {@link TwoPhaseIterator}'s
* {@link TwoPhaseIterator#approximation() approximation} must
* advance synchronously with this iterator: advancing the approximation must
* advance this iterator and vice-versa.
*
* Implementing this method is typically useful on {@link Scorer}s
* that have a high per-document overhead in order to confirm matches.
*
* The default implementation returns {@code null}.
*/
public TwoPhaseIterator asTwoPhaseIterator() {
return null;
}
}