/*
* Copyright 2004 The Apache Software Foundation
*
* Licensed 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>An abstract base class for simple, character-oriented tokenizers.</summary>
public abstract class CharTokenizer : Tokenizer
{
public CharTokenizer(System.IO.TextReader input) : base(input)
{
}
private int offset = 0, bufferIndex = 0, dataLen = 0;
private const int MAX_WORD_LEN = 255;
private const int IO_BUFFER_SIZE = 1024;
private char[] buffer = new char[MAX_WORD_LEN];
private char[] ioBuffer = new char[IO_BUFFER_SIZE];
/// <summary>Returns true iff a character should be included in a token. This
/// tokenizer generates as tokens adjacent sequences of characters which
/// satisfy this predicate. Characters for which this is false are used to
/// define token boundaries and are not included in tokens.
/// </summary>
protected internal abstract bool IsTokenChar(char c);
/// <summary>Called on each token character to normalize it before it is added to the
/// token. The default implementation does nothing. Subclasses may use this
/// to, e.g., lowercase tokens.
/// </summary>
protected internal virtual char Normalize(char c)
{
return c;
}
/// <summary>Returns the next token in the stream, or null at EOS. </summary>
public override Token Next()
{
int length = 0;
int start = offset;
while (true)
{
char c;
offset++;
if (bufferIndex >= dataLen)
{
dataLen = input.Read((System.Char[]) ioBuffer, 0, ioBuffer.Length);
bufferIndex = 0;
}
;
if (dataLen <= 0)
{
if (length > 0)
break;
else
return null;
}
else
c = ioBuffer[bufferIndex++];
if (IsTokenChar(c))
{
// if it's a token char
if (length == 0)
// start of token
start = offset - 1;
buffer[length++] = Normalize(c); // buffer it, normalized
if (length == MAX_WORD_LEN)
// buffer overflow!
break;
}
else if (length > 0)
// at non-Letter w/ chars
break; // return 'em
}
return new Token(new System.String(buffer, 0, length), start, start + length);
}
}
}
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