## org.apache.lucene.analysis
Class ASCIIFoldingFilter

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

All Implemented Interfaces:
  Closeable

    public final class ASCIIFoldingFilter

extends TokenFilter

This class converts alphabetic, numeric, and symbolic Unicode characters which are not in the first 127 ASCII characters (the "Basic Latin" Unicode block) into their ASCII equivalents, if one exists. Characters from the following Unicode blocks are converted; however, only those characters with reasonable ASCII alternatives are converted:

- C1 Controls and Latin-1 Supplement: http://www.unicode.org/charts/PDF/U0080.pdf
- Latin Extended-A: http://www.unicode.org/charts/PDF/U0100.pdf
- Latin Extended-B: http://www.unicode.org/charts/PDF/U0180.pdf
- Latin Extended Additional: http://www.unicode.org/charts/PDF/U1E00.pdf
- Latin Extended-C: http://www.unicode.org/charts/PDF/U2C60.pdf
- Latin Extended-D: http://www.unicode.org/charts/PDF/UA720.pdf
- IPA Extensions: http://www.unicode.org/charts/PDF/U0250.pdf
- Phonetic Extensions: http://www.unicode.org/charts/PDF/U1D00.pdf
- Phonetic Extensions Supplement: http://www.unicode.org/charts/PDF/U1D80.pdf
- General Punctuation: http://www.unicode.org/charts/PDF/U2000.pdf
- Superscripts and Subscripts: http://www.unicode.org/charts/PDF/U2070.pdf
- Enclosed Alphanumerics: http://www.unicode.org/charts/PDF/U2460.pdf
- Dingbats: http://www.unicode.org/charts/PDF/U2700.pdf
- Supplemental Punctuation: http://www.unicode.org/charts/PDF/U2E00.pdf
- Alphabetic Presentation Forms: http://www.unicode.org/charts/PDF/UFB00.pdf
- Halfwidth and Fullwidth Forms: http://www.unicode.org/charts/PDF/UFF00.pdf

See: http://en.wikipedia.org/wiki/Latin_characters_in_Unicode The set of character conversions supported by this class is a superset of those supported by Lucene's `ISOLatin1AccentFilter` which strips accents from Latin1 characters. For example, 'à' will be replaced by 'a'.

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
`ASCIIFoldingFilter(TokenStream input)`

Method Summary
`void` `foldToASCII(char[] input, int length)` Converts characters above ASCII to their ASCII equivalents.
`static int` `foldToASCII(char[] input, int inputPos, char[] output, int outputPos, int length)` Converts characters above ASCII to their ASCII equivalents.
`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

### ASCIIFoldingFilter

    public ASCIIFoldingFilter(TokenStream input)

Method Detail

### incrementToken

    public 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`

### foldToASCII

    public void foldToASCII(char[] input,
                            int length)

  Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

  Parameters:
    `input` - The string to fold
    `length` - The number of characters in the input string

### foldToASCII

    public static final int foldToASCII(char[] input,
                                        int inputPos,
                                        char[] output,
                                        int outputPos,
                                        int length)

  Converts characters above ASCII to their ASCII equivalents. For example, accents are removed from accented characters.

  Parameters:
    `input` - The characters to fold
    `inputPos` - Index of the first character to fold
    `output` - The result of the folding. Should be of size >= `length * 4`.
    `outputPos` - Index of output where to put the result of the folding
    `length` - The number of characters to fold
  Returns:
    length of output
  NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.