SortComparator.java

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.index.IndexReader;

import java.io.IOException;

/**
 * Abstract base class for sorting hits returned by a Query.
 * 
 * <p>
 * This class should only be used if the other SortField types (SCORE, DOC,
 * STRING, INT, FLOAT) do not provide an adequate sorting. It maintains an
 * internal cache of values which could be quite large. The cache is an array of
 * Comparable, one for each document in the index. There is a distinct
 * Comparable for each unique term in the field - if some documents have the
 * same term in the field, the cache array will have entries which reference the
 * same Comparable.
 * 
 * This class will be used as part of a key to a FieldCache value. You must
 * implement hashCode and equals to avoid an explosion in RAM usage if you use
 * instances that are not the same instance. If you are searching using the
 * Remote contrib, the same instance of this class on the client will be a new
 * instance on every call to the server, so hashCode/equals is very important in
 * that situation.
 * 
 * <p>
 * Created: Apr 21, 2004 5:08:38 PM
 * 
 * 
 * @version $Id: SortComparator.java 800119 2009-08-02 17:59:21Z markrmiller $
 * @since 1.4
 * @deprecated Please use {@link FieldComparatorSource} instead.
 */
public abstract class SortComparator
implements SortComparatorSource {

  // inherit javadocs
  public ScoreDocComparator newComparator (final IndexReader reader, final String fieldname)
  throws IOException {
    final String field = fieldname.intern();
    final Comparable[] cachedValues = FieldCache.DEFAULT.getCustom (reader, field, SortComparator.this);
    
    return new ScoreDocComparator() {

      public int compare (ScoreDoc i, ScoreDoc j) {
        return cachedValues[i.doc].compareTo (cachedValues[j.doc]);
      }

      public Comparable sortValue (ScoreDoc i) {
        return cachedValues[i.doc];
      }

      public int sortType(){
        return SortField.CUSTOM;
      }
    };
  }

  /**
   * Returns an object which, when sorted according to natural order,
   * will order the Term values in the correct order.
   * <p>For example, if the Terms contained integer values, this method
   * would return <code>new Integer(termtext)</code>.  Note that this
   * might not always be the most efficient implementation - for this
   * particular example, a better implementation might be to make a
   * ScoreDocLookupComparator that uses an internal lookup table of int.
   * @param termtext The textual value of the term.
   * @return An object representing <code>termtext</code> that sorts according to the natural order of <code>termtext</code>.
   * @see Comparable
   * @see ScoreDocComparator
   */
  protected abstract Comparable getComparable (String termtext);

}