PorterStemFilter (Lucene 3.6.2 API)
Keywords: org.apache.lucene.analysis.PorterStemFilter class

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## org.apache.lucene.analysis
Class PorterStemFilter

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

All Implemented Interfaces:
  Closeable

    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));
          }
        }

Note: This filter is aware of the `KeywordAttribute`. To prevent certain terms from being passed to the stemmer `KeywordAttribute.isKeyword()` should be set to `true` in a previous `TokenStream`.

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
`PorterStemFilter(TokenStream in)`

Method Summary
`boolean` | `incrementToken()` Consumers (i.e., `IndexWriter`) use this method to advance the stream to the next token.

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, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString`

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

Constructor Detail

### PorterStemFilter

    public PorterStemFilter(TokenStream in)

Method Detail

### incrementToken

    public final boolean incrementToken()
                                 throws IOException

  Description copied from class: `TokenStream`
  Consumers (i.e., `IndexWriter`) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate `AttributeImpl`s 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 `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 `AttributeSource.addAttribute(Class)` and `AttributeSource.getAttribute(Class)`, references to all `AttributeImpl`s 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 `TokenStream.incrementToken()`.

  Specified by:
    `incrementToken` in class `TokenStream`
  Returns:
    false for end of stream; true otherwise
  Throws:
    `IOException`

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