porterstemfilter.cs

Lucene.Net 版本源码 测试通过

/*
 * 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.
 */

using System;

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>
    /// <PRE>
    /// class MyAnalyzer extends Analyzer {
    /// public final TokenStream tokenStream(String fieldName, Reader reader) {
    /// return new PorterStemFilter(new LowerCaseTokenizer(reader));
    /// }
    /// }
    /// </PRE>
    /// </summary>
    public sealed class PorterStemFilter : TokenFilter
    {
        private PorterStemmer stemmer;
		
        public PorterStemFilter(TokenStream in_Renamed) : base(in_Renamed)
        {
            stemmer = new PorterStemmer();
        }
		
        /// <summary>Returns the next input Token, after being stemmed </summary>
        public override Token Next()
        {
            Token token = input.Next();
            if (token == null)
                return null;
            else
            {
                System.String s = stemmer.Stem(token.termText);
                if ((System.Object) s != (System.Object) token.termText)
                    // Yes, I mean object reference comparison here
                    token.termText = s;
                return token;
            }
        }
    }
}