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StopFilter.javaAPI DocApache Lucene 2.0.03608Fri May 26 09:54:14 BST 2006org.apache.lucene.analysis

StopFilter

public final class StopFilter extends TokenFilter
Removes stop words from a token stream.

Fields Summary
private final Set
stopWords
private final boolean
ignoreCase
Constructors Summary
public StopFilter(TokenStream input, String[] stopWords)
Construct a token stream filtering the given input.

        this(input, stopWords, false);
public StopFilter(TokenStream in, String[] stopWords, boolean ignoreCase)
Constructs a filter which removes words from the input TokenStream that are named in the array of words.

    super(in);
    this.ignoreCase = ignoreCase;
    this.stopWords = makeStopSet(stopWords, ignoreCase);
public StopFilter(TokenStream input, Set stopWords, boolean ignoreCase)
Construct a token stream filtering the given input.

param
input
param
stopWords The set of Stop Words, as Strings. If ignoreCase is true, all strings should be lower cased
param
ignoreCase -Ignore case when stopping. The stopWords set must be setup to contain only lower case words

        super(input);
        this.ignoreCase = ignoreCase;
        this.stopWords = stopWords;
public StopFilter(TokenStream in, Set stopWords)
Constructs a filter which removes words from the input TokenStream that are named in the Set. It is crucial that an efficient Set implementation is used for maximum performance.

see
#makeStopSet(java.lang.String[])

    this(in, stopWords, false);
Methods Summary
public static final java.util.SetmakeStopSet(java.lang.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
#makeStopSet(java.lang.String[], boolean) passing false to ignoreCase

    return makeStopSet(stopWords, false);
public static final java.util.SetmakeStopSet(java.lang.String[] stopWords, boolean ignoreCase)

param
stopWords
param
ignoreCase If true, all words are lower cased first.
return
a Set containing the words

    HashSet stopTable = new HashSet(stopWords.length);
    for (int i = 0; i < stopWords.length; i++)
      stopTable.add(ignoreCase ? stopWords[i].toLowerCase() : stopWords[i]);
    return stopTable;
public final org.apache.lucene.analysis.Tokennext()
Returns the next input Token whose termText() is not a stop word.

    // return the first non-stop word found
    for (Token token = input.next(); token != null; token = input.next())
    {
        String termText = ignoreCase ? token.termText.toLowerCase() : token.termText;
        if (!stopWords.contains(termText))
          return token;
    }
    // reached EOS -- return null
    return null;