SortComparator


1   package org.apache.lucene.search;
2   
3   import org.apache.lucene.index.IndexReader;
4   
5   import java.io.IOException  ;
6   
7   /**
8    * Abstract base class for sorting hits returned by a Query.
9    *
10   * <p>This class should only be used if the other SortField
11   * types (SCORE, DOC, STRING, INT, FLOAT) do not provide an
12   * adequate sorting.  It maintains an internal cache of values which
13   * could be quite large.  The cache is an array of Comparable,
14   * one for each document in the index.  There is a distinct
15   * Comparable for each unique term in the field - if
16   * some documents have the same term in the field, the cache
17   * array will have entries which reference the same Comparable.
18   *
19   * <p>Created: Apr 21, 2004 5:08:38 PM
20   *
21   * @author  Tim Jones
22   * @version $Id: SortComparator.java 150541 2004-09-29 15:09:02Z goller $
23   * @since   1.4
24   */
25  public abstract class SortComparator
26  implements SortComparatorSource {
27  
28    // inherit javadocs
29    public ScoreDocComparator newComparator (final IndexReader reader, final String   fieldname)
30    throws IOException   {
31      final String   field = fieldname.intern();
32      final Comparable  [] cachedValues = FieldCache.DEFAULT.getCustom (reader, field, SortComparator.this);
33      
34      return new ScoreDocComparator() {
35  
36        public int compare (ScoreDoc i, ScoreDoc j) {
37          return cachedValues[i.doc].compareTo (cachedValues[j.doc]);
38        }
39  
40        public Comparable   sortValue (ScoreDoc i) {
41          return cachedValues[i.doc];
42        }
43  
44        public int sortType(){
45          return SortField.CUSTOM;
46        }
47      };
48    }
49  
50    /**
51     * Returns an object which, when sorted according to natural order,
52     * will order the Term values in the correct order.
53     * <p>For example, if the Terms contained integer values, this method
54     * would return <code>new Integer(termtext)</code>.  Note that this
55     * might not always be the most efficient implementation - for this
56     * particular example, a better implementation might be to make a
57     * ScoreDocLookupComparator that uses an internal lookup table of int.
58     * @param termtext The textual value of the term.
59     * @return An object representing <code>termtext</code> that sorts according to the natural order of <code>termtext</code>.
60     * @see Comparable
61     * @see ScoreDocComparator
62     */
63    protected abstract Comparable   getComparable (String   termtext);
64  
65  }
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