PorterStemFilter (Lucene 2.4.1 API)
Keywords: org.apache.lucene.analysis.PorterStemFilter class

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## org.apache.lucene.analysis
Class PorterStemFilter

    java.lang.Object
      org.apache.lucene.analysis.TokenStream
          org.apache.lucene.analysis.TokenFilter
              org.apache.lucene.analysis.PorterStemFilter

    public final class PorterStemFilter

extends TokenFilter

Transforms the token stream as per the Porter stemming algorithm. Note: the input to the stemming filter must already be in lower case, so you will need to use LowerCaseFilter or LowerCaseTokenizer farther down the Tokenizer chain in order for this to work properly!

To use this filter with other analyzers, you'll want to write an Analyzer class that sets up the TokenStream chain as you want it. To use this with LowerCaseTokenizer, for example, you'd write an analyzer like this:

        class MyAnalyzer extends Analyzer {
          public final TokenStream tokenStream(String fieldName, Reader reader) {
            return new PorterStemFilter(new LowerCaseTokenizer(reader));
          }
        }

Field Summary

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

Constructor Summary
`PorterStemFilter(TokenStream in)`

Method Summary
`Token` | `next(Token reusableToken)` Returns the next token in the stream, or null at EOS.

Methods inherited from class org.apache.lucene.analysis.TokenFilter
`close, reset`

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

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### PorterStemFilter

    public PorterStemFilter(TokenStream in)

Method Detail

### next

    public final Token next(Token reusableToken)
                     throws IOException

  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 & 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`

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