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

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Here is the source code for org.apache.lucene.search.HitQueue.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 org.apache.lucene.util.PriorityQueue;

final class HitQueue extends PriorityQueue<ScoreDoc> {

    /**
     * Creates a new instance with <code>size</code> elements. If
     * <code>prePopulate</code> is set to true, the queue will pre-populate itself
     * with sentinel objects and set its {@link #size()} to <code>size</code>. In
     * that case, you should not rely on {@link #size()} to get the number of
     * actual elements that were added to the queue, but keep track yourself.<br>
     * <b>NOTE:</b> in case <code>prePopulate</code> is true, you should pop
     * elements from the queue using the following code example:
     * 
     * <pre class="prettyprint">
     * PriorityQueue&lt;ScoreDoc&gt; pq = new HitQueue(10, true); // pre-populate.
     * ScoreDoc top = pq.top();
     * 
     * // Add/Update one element.
     * top.score = 1.0f;
     * top.doc = 0;
     * top = (ScoreDoc) pq.updateTop();
     * int totalHits = 1;
     * 
     * // Now pop only the elements that were *truly* inserted.
     * // First, pop all the sentinel elements (there are pq.size() - totalHits).
     * for (int i = pq.size() - totalHits; i &gt; 0; i--) pq.pop();
     * 
     * // Now pop the truly added elements.
     * ScoreDoc[] results = new ScoreDoc[totalHits];
     * for (int i = totalHits - 1; i &gt;= 0; i--) {
     *   results[i] = (ScoreDoc) pq.pop();
     * }
     * </pre>
     * 
     * <p><b>NOTE</b>: This class pre-allocate a full array of
     * length <code>size</code>.
     * 
     * @param size
     *          the requested size of this queue.
     * @param prePopulate
     *          specifies whether to pre-populate the queue with sentinel values.
     */
    HitQueue(int size, boolean prePopulate) {
        super(size, () -> {
            if (prePopulate) {
                // Always set the doc Id to MAX_VALUE so that it won't be favored by
                // lessThan. This generally should not happen since if score is not NEG_INF,
                // TopScoreDocCollector will always add the object to the queue.
                return new ScoreDoc(Integer.MAX_VALUE, Float.NEGATIVE_INFINITY);
            } else {
                return null;
            }
        });
    }

    @Override
    protected final boolean lessThan(ScoreDoc hitA, ScoreDoc hitB) {
        if (hitA.score == hitB.score)
            return hitA.doc > hitB.doc;
        else
            return hitA.score < hitB.score;
    }
}