topdoccollector.java

Lucene a java open-source SearchEngine Framework

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;

/** A {@link HitCollector} implementation that collects the top-scoring
 * documents, returning them as a {@link TopDocs}.  This is used by {@link
 * IndexSearcher} to implement {@link TopDocs}-based search.
 *
 * <p>This may be extended, overriding the collect method to, e.g.,
 * conditionally invoke <code>super()</code> in order to filter which
 * documents are collected.
 **/
public class TopDocCollector extends HitCollector {

  private ScoreDoc reusableSD;

  int totalHits;
  PriorityQueue hq;
    
  /** Construct to collect a given number of hits.
   * @param numHits the maximum number of hits to collect
   */
  public TopDocCollector(int numHits) {
    this(numHits, new HitQueue(numHits));
  }

  TopDocCollector(int numHits, PriorityQueue hq) {
    this.hq = hq;
  }

  // javadoc inherited
  public void collect(int doc, float score) {
    if (score > 0.0f) {
      totalHits++;
      if (reusableSD == null) {
        reusableSD = new ScoreDoc(doc, score);
      } else if (score >= reusableSD.score) {
        // reusableSD holds the last "rejected" entry, so, if
        // this new score is not better than that, there's no
        // need to try inserting it
        reusableSD.doc = doc;
        reusableSD.score = score;
      } else {
        return;
      }
      reusableSD = (ScoreDoc) hq.insertWithOverflow(reusableSD);
    }
  }

  /** The total number of documents that matched this query. */
  public int getTotalHits() { return totalHits; }

  /** The top-scoring hits. */
  public TopDocs topDocs() {
    ScoreDoc[] scoreDocs = new ScoreDoc[hq.size()];
    for (int i = hq.size()-1; i >= 0; i--)      // put docs in array
      scoreDocs[i] = (ScoreDoc)hq.pop();
      
    float maxScore = (totalHits==0)
      ? Float.NEGATIVE_INFINITY
      : scoreDocs[0].score;
    
    return new TopDocs(totalHits, scoreDocs, maxScore);
  }
}