org.apache.lucene.analysis.ngram

Class NGramTokenizer

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.Tokenizer

org.apache.lucene.analysis.ngram.NGramTokenizer

public class NGramTokenizer
extends Tokenizer

Tokenizes the input into n-grams of the given size(s).

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_MAX_NGRAM_SIZE
static int	DEFAULT_MIN_NGRAM_SIZE

Fields inherited from class org.apache.lucene.analysis.Tokenizer

input

Constructor Summary

Constructors

Constructor and Description
NGramTokenizer(AttributeSource.AttributeFactory factory, Reader input, int minGram, int maxGram) Creates NGramTokenizer with given min and max n-grams.
NGramTokenizer(AttributeSource source, Reader input, int minGram, int maxGram) Creates NGramTokenizer with given min and max n-grams.
NGramTokenizer(Reader input) Creates NGramTokenizer with default min and max n-grams.
NGramTokenizer(Reader input, int minGram, int maxGram) Creates NGramTokenizer with given min and max n-grams.

Method Summary

Methods

Modifier and Type	Method and Description
void	end() This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API).
boolean	incrementToken() Returns the next token in the stream, or null at EOS.
Token	next() Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
Token	next(Token reusableToken) Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
void	reset() Resets this stream to the beginning.
void	reset(Reader input) Expert: Reset the tokenizer to a new reader.

Methods inherited from class org.apache.lucene.analysis.Tokenizer

close, correctOffset

Methods inherited from class org.apache.lucene.analysis.TokenStream

getOnlyUseNewAPI, setOnlyUseNewAPI

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, restoreState, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_MIN_NGRAM_SIZE

public static final int DEFAULT_MIN_NGRAM_SIZE

See Also:

Constant Field Values

DEFAULT_MAX_NGRAM_SIZE

public static final int DEFAULT_MAX_NGRAM_SIZE

See Also:

Constant Field Values

Constructor Detail

NGramTokenizer

public NGramTokenizer(Reader input,
              int minGram,
              int maxGram)

Creates NGramTokenizer with given min and max n-grams.

Parameters:

input - Reader holding the input to be tokenized

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

NGramTokenizer

public NGramTokenizer(AttributeSource source,
              Reader input,
              int minGram,
              int maxGram)

Creates NGramTokenizer with given min and max n-grams.

Parameters:

source - AttributeSource to use

input - Reader holding the input to be tokenized

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

NGramTokenizer

public NGramTokenizer(AttributeSource.AttributeFactory factory,
              Reader input,
              int minGram,
              int maxGram)

Creates NGramTokenizer with given min and max n-grams.

Parameters:

factory - AttributeSource.AttributeFactory to use

input - Reader holding the input to be tokenized

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

NGramTokenizer

public NGramTokenizer(Reader input)

Creates NGramTokenizer with default min and max n-grams.

Parameters:

input - Reader holding the input to be tokenized

Method Detail

incrementToken

public final boolean incrementToken()
                             throws IOException

Returns the next token in the stream, or null at EOS.

Overrides:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

Note that this method will be defined abstract in Lucene 3.0.

Throws:

IOException

end

public final void end()

Description copied from class: TokenStream

This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new 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.

Overrides:

end in class TokenStream

next

public final Token next(Token reusableToken)
                 throws IOException

Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream

Returns the next token in the stream, or null at EOS. When possible, the input Token should be used as the returned Token (this gives fastest tokenization performance), but this is not required and a new Token may be returned. Callers may re-use a single Token instance for successive calls to this method.

This implicitly defines a "contract" between consumers (callers of this method) and producers (implementations of this method that are the source for tokens):

• A consumer must fully consume the previously returned Token before calling this method again.
• A producer must call Token.clear() before setting the fields in it and returning it

Also, the producer must make no assumptions about a Token after it has been returned: the caller may arbitrarily change it. If the producer needs to hold onto the Token for subsequent calls, it must clone() it before storing it. Note that a TokenFilter is considered a consumer.

Overrides:

next in class TokenStream

Parameters:

reusableToken - a Token that may or may not be used to return; this parameter should never be null (the callee is not required to check for null before using it, but it is a good idea to assert that it is not null.)

Returns:

next Token in the stream or null if end-of-stream was hit

Throws:

IOException

next

public final Token next()
                 throws IOException

Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream

Returns the next Token in the stream, or null at EOS.

Overrides:

next in class TokenStream

Throws:

IOException

reset

public void reset(Reader input)
           throws IOException

Description copied from class: Tokenizer

Expert: Reset the tokenizer to a new reader. Typically, an analyzer (in its reusableTokenStream method) will use this to re-use a previously created tokenizer.

Overrides:

reset in class Tokenizer

Throws:

IOException

reset

public void reset()
           throws IOException

Description copied from class: TokenStream

Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. TokenStream.reset() is not needed for the standard indexing process. However, if the tokens of a TokenStream are intended to be consumed more than once, it is necessary to implement TokenStream.reset(). Note that if your TokenStream caches tokens and feeds them back again after a reset, it is imperative that you clone the tokens when you store them away (on the first pass) as well as when you return them (on future passes after TokenStream.reset()).

Overrides:

reset in class TokenStream

Throws:

IOException