PorterStemFilter.cs

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/* 
 * 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
 * 
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 * distributed under the License is distributed on an "AS IS" BASIS,
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using Lucene.Net.Analysis.Tokenattributes;

namespace Lucene.Net.Analysis
{
    
    /// <summary>Transforms the token stream as per the Porter stemming algorithm.
    /// Note: the input to the stemming filter must already be in lower case,
    /// so you will need to use LowerCaseFilter or LowerCaseTokenizer farther
    /// down the Tokenizer chain in order for this to work properly!
    /// <p/>
    /// To use this filter with other analyzers, you'll want to write an
    /// Analyzer class that sets up the TokenStream chain as you want it.
    /// To use this with LowerCaseTokenizer, for example, you'd write an
    /// analyzer like this:
    /// <p/>
    /// <code>
    /// class MyAnalyzer extends Analyzer {
    ///     public final TokenStream tokenStream(String fieldName, Reader reader) {
    ///          return new PorterStemFilter(new LowerCaseTokenizer(reader));
    ///     }
    /// }
    /// </code>
    /// </summary>
    public sealed class PorterStemFilter:TokenFilter
    {
        private readonly PorterStemmer stemmer;
        private readonly ITermAttribute termAtt;
        
        public PorterStemFilter(TokenStream in_Renamed):base(in_Renamed)
        {
            stemmer = new PorterStemmer();
            termAtt = AddAttribute<ITermAttribute>();
        }
        
        public override bool IncrementToken()
        {
            if (!input.IncrementToken())
                return false;
            
            if (stemmer.Stem(termAtt.TermBuffer(), 0, termAtt.TermLength()))
                termAtt.SetTermBuffer(stemmer.ResultBuffer, 0, stemmer.ResultLength);
            return true;
        }
    }
}