org.apache.lucene.analysis
Class StopFilter

java.lang.Object
  org.apache.lucene.util.AttributeSource
      org.apache.lucene.analysis.TokenStream
          org.apache.lucene.analysis.TokenFilter
              org.apache.lucene.analysis.StopFilter

All Implemented Interfaces:

Closeable

public final class StopFilter
extends TokenFilter

Removes stop words from a token stream.

Nested Class Summary

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

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

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

input

Constructor Summary

StopFilter(boolean enablePositionIncrements, TokenStream in, Set<?> stopWords)
Constructs a filter which removes words from the input TokenStream that are named in the Set.

StopFilter(boolean enablePositionIncrements, TokenStream input, Set<?> stopWords, boolean ignoreCase)
Construct a token stream filtering the given input.

Method Summary

boolean	getEnablePositionIncrements()
static boolean	getEnablePositionIncrementsVersionDefault(Version matchVersion) Returns version-dependent default for enablePositionIncrements.
boolean	incrementToken() Returns the next input Token whose term() is not a stop word.
static Set<Object>	makeStopSet(List<?> stopWords) Builds a Set from an array of stop words, appropriate for passing into the StopFilter constructor.
static Set<Object>	makeStopSet(List<?> stopWords, boolean ignoreCase)
static Set<Object>	makeStopSet(String... stopWords) Builds a Set from an array of stop words, appropriate for passing into the StopFilter constructor.
static Set<Object>	makeStopSet(String[] stopWords, boolean ignoreCase)
void	setEnablePositionIncrements(boolean enable) If true, this StopFilter will preserve positions of the incoming tokens (ie, accumulate and set position increments of the removed stop tokens).

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

close, end, reset

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

Constructor Detail

StopFilter

public StopFilter(boolean enablePositionIncrements,
                  TokenStream input,
                  Set<?> stopWords,
                  boolean ignoreCase)

Construct a token stream filtering the given input. If stopWords is an instance of CharArraySet (true if makeStopSet() was used to construct the set) it will be directly used and ignoreCase will be ignored since CharArraySet directly controls case sensitivity.

If stopWords is not an instance of CharArraySet, a new CharArraySet will be constructed and ignoreCase will be used to specify the case sensitivity of that set.

Parameters:

enablePositionIncrements - true if token positions should record the removed stop words

input - Input TokenStream

stopWords - A Set of Strings or char[] or any other toString()-able set representing the stopwords

ignoreCase - if true, all words are lower cased first

StopFilter

public StopFilter(boolean enablePositionIncrements,
                  TokenStream in,
                  Set<?> stopWords)

Constructs a filter which removes words from the input TokenStream that are named in the Set.

Parameters:

enablePositionIncrements - true if token positions should record the removed stop words

in - Input stream

stopWords - A Set of Strings or char[] or any other toString()-able set representing the stopwords

See Also:

makeStopSet(java.lang.String[])

Method Detail

makeStopSet

public static final Set<Object> makeStopSet(String... stopWords)

Builds a Set from an array of stop words, appropriate for passing into the StopFilter constructor. This permits this stopWords construction to be cached once when an Analyzer is constructed.

See Also:

passing false to ignoreCase

makeStopSet

public static final Set<Object> makeStopSet(List<?> stopWords)

Builds a Set from an array of stop words, appropriate for passing into the StopFilter constructor. This permits this stopWords construction to be cached once when an Analyzer is constructed.

Parameters:

stopWords - A List of Strings or char[] or any other toString()-able list representing the stopwords

Returns:

A Set (CharArraySet) containing the words

See Also:

passing false to ignoreCase

makeStopSet

public static final Set<Object> makeStopSet(String[] stopWords,
                                            boolean ignoreCase)

Parameters:

stopWords - An array of stopwords

ignoreCase - If true, all words are lower cased first.

Returns:

a Set containing the words

makeStopSet

public static final Set<Object> makeStopSet(List<?> stopWords,
                                            boolean ignoreCase)

Parameters:

stopWords - A List of Strings or char[] or any other toString()-able list representing the stopwords

ignoreCase - if true, all words are lower cased first

Returns:

A Set (CharArraySet) containing the words

incrementToken

public final boolean incrementToken()
                             throws IOException

Returns the next input Token whose term() is not a stop word.

Specified by:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

Throws:

IOException

getEnablePositionIncrementsVersionDefault

public static boolean getEnablePositionIncrementsVersionDefault(Version matchVersion)

Returns version-dependent default for enablePositionIncrements. Analyzers that embed StopFilter use this method when creating the StopFilter. Prior to 2.9, this returns false. On 2.9 or later, it returns true.

getEnablePositionIncrements

public boolean getEnablePositionIncrements()

See Also:

setEnablePositionIncrements(boolean).

setEnablePositionIncrements

public void setEnablePositionIncrements(boolean enable)

If true, this StopFilter will preserve positions of the incoming tokens (ie, accumulate and set position increments of the removed stop tokens). Generally, true is best as it does not lose information (positions of the original tokens) during indexing.

When set, when a token is stopped (omitted), the position increment of the following token is incremented.

NOTE: be sure to also set QueryParser.setEnablePositionIncrements(boolean) if you use QueryParser to create queries.