src/java.base/share/classes/java/text/Normalizer.java

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/*
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 * (C) Copyright IBM Corp. 1996-2005 - All Rights Reserved                     *
 *                                                                             *
 * The original version of this source code and documentation is copyrighted   *
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 */

package java.text;

import jdk.internal.icu.text.NormalizerBase;

/**
 * This class provides the method {@code normalize} which transforms Unicode
 * text into an equivalent composed or decomposed form, allowing for easier
 * sorting and searching of text.
 * The {@code normalize} method supports the standard normalization forms
 * described in
 * <a href="https://www.unicode.org/reports/tr15/">
 * Unicode Standard Annex #15 &mdash; Unicode Normalization Forms</a>.
 * <p>
 * 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):
 *
 * <pre>
 *      U+00C1    LATIN CAPITAL LETTER A WITH ACUTE</pre>
 *
 * or as two separate characters (the "decomposed" form):
 *
 * <pre>
 *      U+0041    LATIN CAPITAL LETTER A
 *      U+0301    COMBINING ACUTE ACCENT</pre>
 *
 * 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.
 * <p>
 * Similarly, the string "ffi" can be encoded as three separate letters:
 *
 * <pre>
 *      U+0066    LATIN SMALL LETTER F
 *      U+0066    LATIN SMALL LETTER F
 *      U+0069    LATIN SMALL LETTER I</pre>
 *
 * or as the single character
 *
 * <pre>
 *      U+FB03    LATIN SMALL LIGATURE FFI</pre>
 *
 * 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.
 * <p>
 * The {@code 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 {@code normalize} method rearranges accents into the
 * proper canonical order, so that you do not have to worry about accent
 * rearrangement on your own.
 * <p>
 * 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.
 *
 * @spec https://www.unicode.org/reports/tr15 Unicode Normalization Forms
 * @since 1.6
 */
public final class Normalizer {

   private Normalizer() {};

    /**
     * This enum provides constants of the four Unicode normalization forms
     * that are described in
     * <a href="https://www.unicode.org/reports/tr15/">
     * Unicode Standard Annex #15 &mdash; Unicode Normalization Forms</a>
     * and two methods to access them.
     *
     * @spec https://www.unicode.org/reports/tr15 Unicode Normalization Forms
     * @since 1.6
     */
    public static enum Form {

        /**
         * Canonical decomposition.
         */
        NFD,

        /**
         * Canonical decomposition, followed by canonical composition.
         */
        NFC,

        /**
         * Compatibility decomposition.
         */
        NFKD,

        /**
         * Compatibility decomposition, followed by canonical composition.
         */
        NFKC
    }

    /**
     * Normalize a sequence of char values.
     * The sequence will be normalized according to the specified normalization
     * form.
     * @param src        The sequence of char values to normalize.
     * @param form       The normalization form; one of
     *                   {@link java.text.Normalizer.Form#NFC},
     *                   {@link java.text.Normalizer.Form#NFD},
     *                   {@link java.text.Normalizer.Form#NFKC},
     *                   {@link java.text.Normalizer.Form#NFKD}
     * @return The normalized String
     * @throws NullPointerException If {@code src} or {@code form}
     * is null.
     */
    public static String normalize(CharSequence src, Form form) {
        return NormalizerBase.normalize(src.toString(), form);
    }

    /**
     * Determines if the given sequence of char values is normalized.
     * @param src        The sequence of char values to be checked.
     * @param form       The normalization form; one of
     *                   {@link java.text.Normalizer.Form#NFC},
     *                   {@link java.text.Normalizer.Form#NFD},
     *                   {@link java.text.Normalizer.Form#NFKC},
     *                   {@link java.text.Normalizer.Form#NFKD}
     * @return true if the sequence of char values is normalized;
     * false otherwise.
     * @throws NullPointerException If {@code src} or {@code form}
     * is null.
     */
    public static boolean isNormalized(CharSequence src, Form form) {
        return NormalizerBase.isNormalized(src.toString(), form);
    }
}