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

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Here is the source code for org.apache.lucene.search.TwoPhaseIterator.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;

/**
 * Returned by {@link Scorer#twoPhaseIterator()}
 * to expose an approximation of a {@link DocIdSetIterator}.
 * When the {@link #approximation()}'s
 * {@link DocIdSetIterator#nextDoc()} or {@link DocIdSetIterator#advance(int)}
 * return, {@link #matches()} needs to be checked in order to know whether the
 * returned doc ID actually matches.
 * @lucene.experimental
 */
public abstract class TwoPhaseIterator {

    protected final DocIdSetIterator approximation;

    /** Takes the approximation to be returned by {@link #approximation}. Not null. */
    protected TwoPhaseIterator(DocIdSetIterator approximation) {
        this.approximation = Objects.requireNonNull(approximation);
    }

    /** Return a {@link DocIdSetIterator} view of the provided
     *  {@link TwoPhaseIterator}. */
    public static DocIdSetIterator asDocIdSetIterator(TwoPhaseIterator twoPhaseIterator) {
        return new TwoPhaseIteratorAsDocIdSetIterator(twoPhaseIterator);
    }

    /**
     * If the given {@link DocIdSetIterator} has been created with
     * {@link #asDocIdSetIterator}, then this will return the wrapped
     * {@link TwoPhaseIterator}. Otherwise this returns {@code null}.
     */
    public static TwoPhaseIterator unwrap(DocIdSetIterator iterator) {
        if (iterator instanceof TwoPhaseIteratorAsDocIdSetIterator) {
            return ((TwoPhaseIteratorAsDocIdSetIterator) iterator).twoPhaseIterator;
        } else {
            return null;
        }
    }

    private static class TwoPhaseIteratorAsDocIdSetIterator extends DocIdSetIterator {

        final TwoPhaseIterator twoPhaseIterator;
        final DocIdSetIterator approximation;

        TwoPhaseIteratorAsDocIdSetIterator(TwoPhaseIterator twoPhaseIterator) {
            this.twoPhaseIterator = twoPhaseIterator;
            this.approximation = twoPhaseIterator.approximation;
        }

        @Override
        public int docID() {
            return approximation.docID();
        }

        @Override
        public int nextDoc() throws IOException {
            return doNext(approximation.nextDoc());
        }

        @Override
        public int advance(int target) throws IOException {
            return doNext(approximation.advance(target));
        }

        private int doNext(int doc) throws IOException {
            for (;; doc = approximation.nextDoc()) {
                if (doc == NO_MORE_DOCS) {
                    return NO_MORE_DOCS;
                } else if (twoPhaseIterator.matches()) {
                    return doc;
                }
            }
        }

        @Override
        public long cost() {
            return approximation.cost();
        }
    }

    /** Return an approximation. The returned {@link DocIdSetIterator} is a
     *  superset of the matching documents, and each match needs to be confirmed
     *  with {@link #matches()} in order to know whether it matches or not. */
    public DocIdSetIterator approximation() {
        return approximation;
    }

    /** Return whether the current doc ID that {@link #approximation()} is on matches. This
     *  method should only be called when the iterator is positioned -- ie. not
     *  when {@link DocIdSetIterator#docID()} is {@code -1} or
     *  {@link DocIdSetIterator#NO_MORE_DOCS} -- and at most once. */
    public abstract boolean matches() throws IOException;

    /** An estimate of the expected cost to determine that a single document {@link #matches()}.
     *  This can be called before iterating the documents of {@link #approximation()}.
     *  Returns an expected cost in number of simple operations like addition, multiplication,
     *  comparing two numbers and indexing an array.
     *  The returned value must be positive.
     */
    public abstract float matchCost();

}