org.apache.lucene.search.Scorer.java Source code

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Here is the source code for org.apache.lucene.search.Scorer.java

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/*
 * 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;
import java.util.Objects;

/**
 * Expert: Common scoring functionality for different types of queries.
 *
 * <p>
 * A <code>Scorer</code> exposes an {@link #iterator()} over documents
 * matching a query in increasing order of doc Id.
 * </p>
 * <p>
 * Document scores are computed using a given <code>Similarity</code>
 * implementation.
 * </p>
 *
 * <p><b>NOTE</b>: 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 Scorable {

    /** the Scorer's parent Weight */
    protected final Weight weight;

    /**
     * Constructs a Scorer
     * @param weight The scorers <code>Weight</code>.
     */
    protected Scorer(Weight weight) {
        this.weight = Objects.requireNonNull(weight);
    }

    /** returns parent Weight
     * @lucene.experimental
     */
    public Weight getWeight() {
        return weight;
    }

    /**
     * Return a {@link DocIdSetIterator} over matching documents.
     *
     * The returned iterator will either be positioned on {@code -1} if no
     * documents have been scored yet, {@link DocIdSetIterator#NO_MORE_DOCS}
     * if all documents have been scored already, or the last document id that
     * has been scored otherwise.
     *
     * The returned iterator is a view: calling this method several times will
     * return iterators that have the same state.
     */
    public abstract DocIdSetIterator iterator();

    /**
     * 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 the {@link #iterator()}: advancing the
     * approximation must advance the 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 twoPhaseIterator() {
        return null;
    }

    /**
     * Advance to the block of documents that contains {@code target} in order to
     * get scoring information about this block. This method is implicitly called
     * by {@link DocIdSetIterator#advance(int)} and
     * {@link DocIdSetIterator#nextDoc()} on the returned doc ID. Calling this
     * method doesn't modify the current {@link DocIdSetIterator#docID()}.
     * It returns a number that is greater than or equal to all documents
     * contained in the current block, but less than any doc IDS of the next block.
     * {@code target} must be &gt;= {@link #docID()} as well as all targets that
     * have been passed to {@link #advanceShallow(int)} so far.
     */
    public int advanceShallow(int target) throws IOException {
        return DocIdSetIterator.NO_MORE_DOCS;
    }

    /**
     * Return the maximum score that documents between the last {@code target}
     * that this iterator was {@link #advanceShallow(int) shallow-advanced} to
     * included and {@code upTo} included.
     */
    public abstract float getMaxScore(int upTo) throws IOException;
}