home | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Lucene example source code file (HitQueue.java)

This example Lucene source code file (HitQueue.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

hitqueue, hitqueue, override, override, priorityqueue, priorityqueue, scoredoc, scoredoc

The Lucene HitQueue.java source code

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 org.apache.lucene.util.PriorityQueue;

final class HitQueue extends PriorityQueue<ScoreDoc> {

  private boolean prePopulate;

  /**
   * Creates a new instance with <code>size elements. If
   * <code>prePopulate is set to true, the queue will pre-populate itself
   * with sentinel objects and set its {@link #size()} to <code>size. 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: in case prePopulate is true, you should pop
   * elements from the queue using the following code example:
   * 
   * <pre>
   * PriorityQueue 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 > 0; i--) pq.pop();
   * 
   * // Now pop the truly added elements.
   * ScoreDoc[] results = new ScoreDoc[totalHits];
   * for (int i = totalHits - 1; i >= 0; i--) {
   *   results[i] = (ScoreDoc) pq.pop();
   * }
   * </pre>
   * 
   * <p>NOTE: This class pre-allocate a full array of
   * length <code>size.
   * 
   * @param size
   *          the requested size of this queue.
   * @param prePopulate
   *          specifies whether to pre-populate the queue with sentinel values.
   * @see #getSentinelObject()
   */
  HitQueue(int size, boolean prePopulate) {
    this.prePopulate = prePopulate;
    initialize(size);
  }

  // Returns null if prePopulate is false.
  @Override
  protected ScoreDoc getSentinelObject() {
    // 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 !prePopulate ? null : new ScoreDoc(Integer.MAX_VALUE, Float.NEGATIVE_INFINITY);
  }
  
  @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;
  }
}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene HitQueue.java source code file:



my book on functional programming

 

new blog posts

 

Copyright 1998-2019 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.