src/Lucene.Net.Analysis.Common/Analysis/Core/LowerCaseTokenizer.cs

using J2N;
using Lucene.Net.Util;
using System.Globalization;
using System.IO;

namespace Lucene.Net.Analysis.Core
{
    /*
     * 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.
     */

    /// <summary>
    /// <see cref="LowerCaseTokenizer"/> performs the function of <see cref="LetterTokenizer"/>
    /// and <see cref="LowerCaseFilter"/> together.  It divides text at non-letters and converts
    /// them to lower case.  While it is functionally equivalent to the combination
    /// of <see cref="LetterTokenizer"/> and <see cref="LowerCaseFilter"/>, there is a performance advantage
    /// to doing the two tasks at once, hence this (redundant) implementation.
    /// <para>
    /// Note: this does a decent job for most European languages, but does a terrible
    /// job for some Asian languages, where words are not separated by spaces.
    /// </para>
    /// <para>
    /// You must specify the required <see cref="LuceneVersion"/> compatibility when creating
    /// <see cref="LowerCaseTokenizer"/>:
    /// <list type="bullet">
    ///     <item><description>As of 3.1, <see cref="Util.CharTokenizer"/> uses an int based API to normalize and
    ///     detect token characters. See <see cref="Util.CharTokenizer.IsTokenChar(int)"/> and
    ///     <see cref="Util.CharTokenizer.Normalize(int)"/> for details.</description></item>
    /// </list>
    /// </para>
    /// </summary>
    public sealed class LowerCaseTokenizer : LetterTokenizer
    {
        /// <summary>
        /// Construct a new <see cref="LowerCaseTokenizer"/>.
        /// </summary>
        /// <param name="matchVersion">
        ///          <see cref="LuceneVersion"/> to match
        /// </param>
        /// <param name="in">
        ///          the input to split up into tokens </param>
        public LowerCaseTokenizer(LuceneVersion matchVersion, TextReader @in)
            : base(matchVersion, @in)
        {
        }

        /// <summary>
        /// Construct a new <see cref="LowerCaseTokenizer"/> using a given
        /// <see cref="AttributeSource.AttributeFactory"/>.
        /// </summary>
        /// <param name="matchVersion">
        ///          <see cref="LuceneVersion"/> to match </param>
        /// <param name="factory">
        ///          the attribute factory to use for this <see cref="Tokenizer"/> </param>
        /// <param name="in">
        ///          the input to split up into tokens </param>
        public LowerCaseTokenizer(LuceneVersion matchVersion, AttributeSource.AttributeFactory factory, TextReader @in)
            : base(matchVersion, factory, @in)
        {
        }

        /// <summary>
        /// Converts char to lower case
        /// <see cref="Character.ToLower(int, CultureInfo)"/> in the invariant culture.
        /// </summary>
        protected override int Normalize(int c)
        {
            return Character.ToLower(c, CultureInfo.InvariantCulture); // LUCENENET specific - need to use invariant culture to match Java
        }
    }
}