src/Lucene.Net.Core/Search/HitQueue.cs

namespace Lucene.Net.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.
     */

    using Lucene.Net.Util;

    public sealed class HitQueue : PriorityQueue<ScoreDoc>
    {
        /// <summary>
        /// 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 <seealso cref="#size()"/> to <code>size</code>. In
        /// that case, you should not rely on <seealso cref="#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>.
        /// </summary>
        /// <param name="size">
        ///          the requested size of this queue. </param>
        /// <param name="prePopulate">
        ///          specifies whether to pre-populate the queue with sentinel values. </param>
        /// <seealso cref= #getSentinelObject() </seealso>
        public HitQueue(int size, bool prePopulate)
            : base(size, prePopulate)
        {
        }

        protected internal override ScoreDoc SentinelObject
        {
            get
            {
                // 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(int.MaxValue, float.NegativeInfinity);
            }
        }

        public override bool LessThan(ScoreDoc hitA, ScoreDoc hitB)
        {
            if (hitA.Score == hitB.Score)
            {
                return hitA.Doc > hitB.Doc;
            }
            else
            {
                return hitA.Score < hitB.Score;
            }
        }
    }
}