Class CharTokenizer

An abstract base class for simple, character-oriented tokenizers.

You must specify the required Lucene.Net.Util.LuceneVersion compatibility when creating CharTokenizer:

As of 3.1, CharTokenizer uses an int based API to normalize and detect token codepoints. See IsTokenChar(int) and Normalize(int) for details.

A new CharTokenizer API has been introduced with Lucene 3.1. This API moved from UTF-16 code units to UTF-32 codepoints to eventually add support for supplementary characters. The old char based API has been deprecated and should be replaced with the int based methods IsTokenChar(int) and Normalize(int).

As of Lucene 3.1 each CharTokenizer - constructor expects a Lucene.Net.Util.LuceneVersion argument. Based on the given Lucene.Net.Util.LuceneVersion either the new API or a backwards compatibility layer is used at runtime. For Lucene.Net.Util.LuceneVersion < 3.1 the backwards compatibility layer ensures correct behavior even for indexes build with previous versions of Lucene. If a Lucene.Net.Util.LuceneVersion >= 3.1 is used CharTokenizer requires the new API to be implemented by the instantiated class. Yet, the old char based API is not required anymore even if backwards compatibility must be preserved. CharTokenizer subclasses implementing the new API are fully backwards compatible if instantiated with Lucene.Net.Util.LuceneVersion < 3.1.

Note: If you use a subclass of CharTokenizer with Lucene.Net.Util.LuceneVersion >= 3.1 on an index build with a version < 3.1, created tokens might not be compatible with the terms in your index.

Inheritance

object

AttributeSource

TokenStream

Tokenizer

CharTokenizer

LetterTokenizer

WhitespaceTokenizer

IndicTokenizer

RussianLetterTokenizer

Implements

IDisposable

Inherited Members

Tokenizer.m_input

Tokenizer.Dispose(bool)

Tokenizer.CorrectOffset(int)

Tokenizer.SetReader(TextReader)

TokenStream.Dispose()

AttributeSource.GetAttributeFactory()

AttributeSource.GetAttributeClassesEnumerator()

AttributeSource.GetAttributeImplsEnumerator()

AttributeSource.AddAttributeImpl(Attribute)

AttributeSource.AddAttribute<T>()

AttributeSource.HasAttributes

AttributeSource.HasAttribute<T>()

AttributeSource.GetAttribute<T>()

AttributeSource.ClearAttributes()

AttributeSource.CaptureState()

AttributeSource.RestoreState(AttributeSource.State)

AttributeSource.GetHashCode()

AttributeSource.Equals(object)

AttributeSource.ReflectAsString(bool)

AttributeSource.ReflectWith(IAttributeReflector)

AttributeSource.CloneAttributes()

AttributeSource.CopyTo(AttributeSource)

AttributeSource.ToString()

object.Equals(object, object)

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: Lucene.Net.Analysis.Util

Assembly: Lucene.Net.Analysis.Common.dll

Syntax

public abstract class CharTokenizer : Tokenizer, IDisposable

Constructors

CharTokenizer(LuceneVersion, AttributeFactory, TextReader)

Creates a new CharTokenizer instance

Declaration

protected CharTokenizer(LuceneVersion matchVersion, AttributeSource.AttributeFactory factory, TextReader input)

Parameters

Type	Name	Description
LuceneVersion	matchVersion	Lucene version to match
AttributeSource.AttributeFactory	factory	the attribute factory to use for this Lucene.Net.Analysis.Tokenizer
TextReader	input	the input to split up into tokens

CharTokenizer(LuceneVersion, TextReader)

Creates a new CharTokenizer instance

Declaration

protected CharTokenizer(LuceneVersion matchVersion, TextReader input)

Parameters

Type	Name	Description
LuceneVersion	matchVersion	Lucene version to match
TextReader	input	the input to split up into tokens

Methods

End()

This method is called by the consumer after the last token has been consumed, after Lucene.Net.Analysis.TokenStream.IncrementToken() returned false (using the new Lucene.Net.Analysis.TokenStream API). Streams implementing the old API should upgrade to use this feature.

This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

If you override this method, always call base.End();.

Declaration

public override sealed void End()

Overrides

Lucene.Net.Analysis.TokenStream.End()

Exceptions

Type	Condition
IOException	If an I/O error occurs

IncrementToken()

Consumers (i.e., Lucene.Net.Index.IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate Lucene.Net.Util.IAttributes with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use Lucene.Net.Util.AttributeSource.CaptureState() to create a copy of the current attribute state.

this method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to Lucene.Net.Util.AttributeSource.AddAttribute<T>() and Lucene.Net.Util.AttributeSource.GetAttribute<T>(), references to all Lucene.Net.Util.IAttributes that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in Lucene.Net.Analysis.TokenStream.IncrementToken().

Declaration

public override sealed bool IncrementToken()

Returns

Type	Description
bool	false for end of stream; true otherwise

Overrides

Lucene.Net.Analysis.TokenStream.IncrementToken()

IsTokenChar(int)

Returns true iff a codepoint should be included in a token. This tokenizer generates as tokens adjacent sequences of codepoints which satisfy this predicate. Codepoints for which this is false are used to define token boundaries and are not included in tokens.

Declaration

protected abstract bool IsTokenChar(int c)

Parameters

Type	Name	Description
int	c

Returns

Type	Description
bool

Normalize(int)

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.

Declaration

protected virtual int Normalize(int c)

Parameters

Type	Name	Description
int	c

Returns

Type	Description
int

Reset()

This method is called by a consumer before it begins consumption using Lucene.Net.Analysis.TokenStream.IncrementToken().

Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

If you override this method, always call base.Reset(), otherwise some internal state will not be correctly reset (e.g., Lucene.Net.Analysis.Tokenizer will throw InvalidOperationException on further usage).

Declaration

public override void Reset()

Overrides

Lucene.Net.Analysis.Tokenizer.Reset()

Implements

IDisposable