Normalizer

AI-generated Key Takeaways

• The Normalizer class transforms Unicode text into composed or decomposed forms for easier text processing.

• It handles characters with accents, ligatures, and compatibility decompositions, ensuring consistent text representation.

• The normalize method allows you to apply various normalization forms like NFC, NFD, NFKC, and NFKD to text.

• Using Normalizer improves text sorting, searching, and comparison by treating equivalent characters uniformly.

• The W3C recommends using NFC for text exchange, and it's essential for compatibility with legacy character encodings.

public final class Normalizer extends Object

This class provides the method 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.

Nested Class Summary

enum

Normalizer.Form

The normalization forms supported by the Normalizer.

Public Method Summary

static boolean	isNormalized(CharSequence src, Normalizer.Form form) Determines if the given sequence of char values is normalized.
static String	normalize(CharSequence src, Normalizer.Form form) Normalize the character sequence src according to the normalization method form.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Methods

public static boolean isNormalized (CharSequence src, Normalizer.Form form)

Determines if the given sequence of char values is normalized.

Parameters

src	The sequence of char values to be checked.
form	The normalization form; one of Normalizer.Form.NFC, Normalizer.Form.NFD, Normalizer.Form.NFKC, Normalizer.Form.NFKD

Returns

• true if the sequence of char values is normalized; false otherwise.

Throws

NullPointerException	If src or form is null.

public static String normalize (CharSequence src, Normalizer.Form form)

Normalize the character sequence src according to the normalization method form.

Parameters

src	character sequence to read for normalization
form	normalization form

Returns

• string normalized according to form