beagled/Lucene.Net/Analysis/PorterStemFilter.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 using System;
  17 namespace Lucene.Net.Analysis
  18 {
  19
  20         /// <summary>Transforms the token stream as per the Porter stemming algorithm.
  21         /// Note: the input to the stemming filter must already be in lower case,
  22         /// so you will need to use LowerCaseFilter or LowerCaseTokenizer farther
  23         /// down the Tokenizer chain in order for this to work properly!
  24         /// <P>
  25         /// To use this filter with other analyzers, you'll want to write an
  26         /// Analyzer class that sets up the TokenStream chain as you want it.
  27         /// To use this with LowerCaseTokenizer, for example, you'd write an
  28         /// analyzer like this:
  29         /// <P>
  30         /// <PRE>
  31         /// class MyAnalyzer extends Analyzer {
  32         /// public final TokenStream tokenStream(String fieldName, Reader reader) {
  33         /// return new PorterStemFilter(new LowerCaseTokenizer(reader));
  34         /// }
  35         /// }
  36         /// </PRE>
  37         /// </summary>
  38         public sealed class PorterStemFilter : TokenFilter
  39         {
  40                 private PorterStemmer stemmer;
  41
  42                 public PorterStemFilter(TokenStream in_Renamed) : base(in_Renamed)
  43                 {
  44                         stemmer = new PorterStemmer();
  45                 }
  46
  47                 /// <summary>Returns the next input Token, after being stemmed </summary>
  48                 public override Token Next()
  49                 {
  50                         Token token = input.Next();
  51                         if (token == null)
  52                                 return null;
  53                         else
  54                         {
  55                                 System.String s = stemmer.Stem(token.termText);
  56                                 if ((System.Object) s != (System.Object) token.termText)
  57                                 // Yes, I mean object reference comparison here
  58                                         token.termText = s;
  59                                 return token;
  60                         }
  61                 }
  62         }
  63 }