normalize which transforms Unicode
text into an equivalent composed or decomposed form, allowing for easier
sorting and searching of text.
The normalize method supports the standard normalization forms
described in
Unicode Standard Annex #15 — Unicode Normalization Forms.
Characters with accents or other adornments can be encoded in several different ways in Unicode. For example, take the character A-acute. In Unicode, this can be encoded as a single character (the "composed" form):
U+00C1 LATIN CAPITAL LETTER A WITH ACUTE
or as two separate characters (the "decomposed" form):
U+0041 LATIN CAPITAL LETTER A
U+0301 COMBINING ACUTE ACCENT
To a user of your program, however, both of these sequences should be
treated as the same "user-level" character "A with acute accent". When you
are searching or comparing text, you must ensure that these two sequences are
treated as equivalent. In addition, you must handle characters with more than
one accent. Sometimes the order of a character's combining accents is
significant, while in other cases accent sequences in different orders are
really equivalent.
Similarly, the string "ffi" can be encoded as three separate letters:
U+0066 LATIN SMALL LETTER F
U+0066 LATIN SMALL LETTER F
U+0069 LATIN SMALL LETTER I
or as the single character
U+FB03 LATIN SMALL LIGATURE FFI
The ffi ligature is not a distinct semantic character, and strictly speaking
it shouldn't be in Unicode at all, but it was included for compatibility
with existing character sets that already provided it. The Unicode standard
identifies such characters by giving them "compatibility" decompositions
into the corresponding semantic characters. When sorting and searching, you
will often want to use these mappings.
The normalize method helps solve these problems by transforming
text into the canonical composed and decomposed forms as shown in the first
example above. In addition, you can have it perform compatibility
decompositions so that you can treat compatibility characters the same as
their equivalents.
Finally, the normalize method rearranges accents into the
proper canonical order, so that you do not have to worry about accent
rearrangement on your own.
The W3C generally recommends to exchange texts in NFC. Note also that most legacy character encodings use only precomposed forms and often do not encode any combining marks by themselves. For conversion to such character encodings the Unicode text needs to be normalized to NFC. For more usage examples, see the Unicode Standard Annex.
src The sequence of char values to normalize.form The normalization form; one of
Normalizer.Form.NFCNormalizer.Form.NFDNormalizer.Form.NFKCNormalizer.Form.NFKDjava.lang.NullPointerException If src or form
is null.src The sequence of char values to be checked.form The normalization form; one of
Normalizer.Form.NFCNormalizer.Form.NFDNormalizer.Form.NFKCNormalizer.Form.NFKDjava.lang.NullPointerException If src or form
is null.