phrasepositions.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 java.io.IOException;
import org.apache.lucene.index.*;

/**
 * Position of a term in a document that takes into account the term offset within the phrase. 
 */
final class PhrasePositions {
  int doc;					  // current doc
  int position;					  // position in doc
  int count;					  // remaining pos in this doc
  int offset;					  // position in phrase
  TermPositions tp;				  // stream of positions
  PhrasePositions next;				  // used to make lists
  boolean repeats;       // there's other pp for same term (e.g. query="1st word 2nd word"~1) 

  PhrasePositions(TermPositions t, int o) {
    tp = t;
    offset = o;
  }

  final boolean next() throws IOException {	  // increments to next doc
    if (!tp.next()) {
      tp.close();				  // close stream
      doc = Integer.MAX_VALUE;			  // sentinel value
      return false;
    }
    doc = tp.doc();
    position = 0;
    return true;
  }

  final boolean skipTo(int target) throws IOException {
    if (!tp.skipTo(target)) {
      tp.close();				  // close stream
      doc = Integer.MAX_VALUE;			  // sentinel value
      return false;
    }
    doc = tp.doc();
    position = 0;
    return true;
  }


  final void firstPosition() throws IOException {
    count = tp.freq();				  // read first pos
    nextPosition();
  }

  /**
   * Go to next location of this term current document, and set 
   * <code>position</code> as <code>location - offset</code>, so that a 
   * matching exact phrase is easily identified when all PhrasePositions 
   * have exactly the same <code>position</code>.
   */
  final boolean nextPosition() throws IOException {
    if (count-- > 0) {				  // read subsequent pos's
      position = tp.nextPosition() - offset;
      return true;
    } else
      return false;
  }
}