Collator.java

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 * (C) Copyright Taligent, Inc. 1996-1998 -  All Rights Reserved
 * (C) Copyright IBM Corp. 1996-1998 - All Rights Reserved
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package java.text;

import java.lang.ref.SoftReference;
import java.text.spi.CollatorProvider;
import java.util.Locale;
import java.util.ResourceBundle;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import sun.util.locale.provider.LocaleProviderAdapter;
import sun.util.locale.provider.LocaleServiceProviderPool;


/**
 * The {@code Collator} class performs locale-sensitive
 * {@code String} comparison. You use this class to build
 * searching and sorting routines for natural language text.
 *
 * <p>
 * {@code Collator} is an abstract base class. Subclasses
 * implement specific collation strategies. One subclass,
 * {@code RuleBasedCollator}, is currently provided with
 * the Java Platform and is applicable to a wide set of languages. Other
 * subclasses may be created to handle more specialized needs.
 *
 * <p>
 * Like other locale-sensitive classes, you can use the static
 * factory method, {@code getInstance}, to obtain the appropriate
 * {@code Collator} object for a given locale. You will only need
 * to look at the subclasses of {@code Collator} if you need
 * to understand the details of a particular collation strategy or
 * if you need to modify that strategy.
 *
 * <p>
 * The following example shows how to compare two strings using
 * the {@code Collator} for the default locale.
 * <blockquote>
 * <pre>{@code
 * // Compare two strings in the default locale
 * Collator myCollator = Collator.getInstance();
 * if( myCollator.compare("abc", "ABC") < 0 )
 *     System.out.println("abc is less than ABC");
 * else
 *     System.out.println("abc is greater than or equal to ABC");
 * }</pre>
 * </blockquote>
 *
 * <p>
 * You can set a {@code Collator}'s <em>strength</em> property
 * to determine the level of difference considered significant in
 * comparisons. Four strengths are provided: {@code PRIMARY},
 * {@code SECONDARY}, {@code TERTIARY}, and {@code IDENTICAL}.
 * The exact assignment of strengths to language features is
 * locale dependent.  For example, in Czech, "e" and "f" are considered
 * primary differences, while "e" and "&#283;" are secondary differences,
 * "e" and "E" are tertiary differences and "e" and "e" are identical.
 * The following shows how both case and accents could be ignored for
 * US English.
 * <blockquote>
 * <pre>
 * //Get the Collator for US English and set its strength to PRIMARY
 * Collator usCollator = Collator.getInstance(Locale.US);
 * usCollator.setStrength(Collator.PRIMARY);
 * if( usCollator.compare("abc", "ABC") == 0 ) {
 *     System.out.println("Strings are equivalent");
 * }
 * </pre>
 * </blockquote>
 * <p>
 * For comparing {@code String}s exactly once, the {@code compare}
 * method provides the best performance. When sorting a list of
 * {@code String}s however, it is generally necessary to compare each
 * {@code String} multiple times. In this case, {@code CollationKey}s
 * provide better performance. The {@code CollationKey} class converts
 * a {@code String} to a series of bits that can be compared bitwise
 * against other {@code CollationKey}s. A {@code CollationKey} is
 * created by a {@code Collator} object for a given {@code String}.
 * <br>
 * <strong>Note:</strong> {@code CollationKey}s from different
 * {@code Collator}s can not be compared. See the class description
 * for {@link CollationKey}
 * for an example using {@code CollationKey}s.
 *
 * @see         RuleBasedCollator
 * @see         CollationKey
 * @see         CollationElementIterator
 * @see         Locale
 * @author      Helena Shih, Laura Werner, Richard Gillam
 * @since 1.1
 */

public abstract class Collator
    implements java.util.Comparator<Object>, Cloneable
{
    /**
     * Collator strength value.  When set, only PRIMARY differences are
     * considered significant during comparison. The assignment of strengths
     * to language features is locale dependent. A common example is for
     * different base letters ("a" vs "b") to be considered a PRIMARY difference.
     * @see java.text.Collator#setStrength
     * @see java.text.Collator#getStrength
     */
    public static final int PRIMARY = 0;
    /**
     * Collator strength value.  When set, only SECONDARY and above differences are
     * considered significant during comparison. The assignment of strengths
     * to language features is locale dependent. A common example is for
     * different accented forms of the same base letter ("a" vs "\u00E4") to be
     * considered a SECONDARY difference.
     * @see java.text.Collator#setStrength
     * @see java.text.Collator#getStrength
     */
    public static final int SECONDARY = 1;
    /**
     * Collator strength value.  When set, only TERTIARY and above differences are
     * considered significant during comparison. The assignment of strengths
     * to language features is locale dependent. A common example is for
     * case differences ("a" vs "A") to be considered a TERTIARY difference.
     * @see java.text.Collator#setStrength
     * @see java.text.Collator#getStrength
     */
    public static final int TERTIARY = 2;

    /**
     * Collator strength value.  When set, all differences are
     * considered significant during comparison. The assignment of strengths
     * to language features is locale dependent. A common example is for control
     * characters ("&#092;u0001" vs "&#092;u0002") to be considered equal at the
     * PRIMARY, SECONDARY, and TERTIARY levels but different at the IDENTICAL
     * level.  Additionally, differences between pre-composed accents such as
     * "&#092;u00C0" (A-grave) and combining accents such as "A&#092;u0300"
     * (A, combining-grave) will be considered significant at the IDENTICAL
     * level if decomposition is set to NO_DECOMPOSITION.
     */
    public static final int IDENTICAL = 3;

    /**
     * Decomposition mode value. With NO_DECOMPOSITION
     * set, accented characters will not be decomposed for collation. This
     * is the default setting and provides the fastest collation but
     * will only produce correct results for languages that do not use accents.
     * @see java.text.Collator#getDecomposition
     * @see java.text.Collator#setDecomposition
     */
    public static final int NO_DECOMPOSITION = 0;

    /**
     * Decomposition mode value. With CANONICAL_DECOMPOSITION
     * set, characters that are canonical variants according to Unicode
     * standard will be decomposed for collation. This should be used to get
     * correct collation of accented characters.
     * <p>
     * CANONICAL_DECOMPOSITION corresponds to Normalization Form D as
     * described in
     * <a href="http://www.unicode.org/reports/tr15/">Unicode
     * Standard Annex #15: Unicode Normalization Forms</a>.
     * @see java.text.Collator#getDecomposition
     * @see java.text.Collator#setDecomposition
     */
    public static final int CANONICAL_DECOMPOSITION = 1;

    /**
     * Decomposition mode value. With FULL_DECOMPOSITION
     * set, both Unicode canonical variants and Unicode compatibility variants
     * will be decomposed for collation.  This causes not only accented
     * characters to be collated, but also characters that have special formats
     * to be collated with their norminal form. For example, the half-width and
     * full-width ASCII and Katakana characters are then collated together.
     * FULL_DECOMPOSITION is the most complete and therefore the slowest
     * decomposition mode.
     * <p>
     * FULL_DECOMPOSITION corresponds to Normalization Form KD as
     * described in
     * <a href="http://www.unicode.org/reports/tr15/">Unicode
     * Standard Annex #15: Unicode Normalization Forms</a>.
     * @see java.text.Collator#getDecomposition
     * @see java.text.Collator#setDecomposition
     */
    public static final int FULL_DECOMPOSITION = 2;

    /**
     * Gets the Collator for the current default locale.
     * The default locale is determined by java.util.Locale.getDefault.
     * @return the Collator for the default locale.(for example, en_US)
     * @see java.util.Locale#getDefault
     */
    public static synchronized Collator getInstance() {
        return getInstance(Locale.getDefault());
    }

    /**
     * Gets the Collator for the desired locale.
     * @param desiredLocale the desired locale.
     * @return the Collator for the desired locale.
     * @see java.util.Locale
     * @see java.util.ResourceBundle
     */
    public static Collator getInstance(Locale desiredLocale) {
        SoftReference<Collator> ref = cache.get(desiredLocale);
        Collator result = (ref != null) ? ref.get() : null;
        if (result == null) {
            LocaleProviderAdapter adapter;
            adapter = LocaleProviderAdapter.getAdapter(CollatorProvider.class,
                                                       desiredLocale);
            CollatorProvider provider = adapter.getCollatorProvider();
            result = provider.getInstance(desiredLocale);
            if (result == null) {
                result = LocaleProviderAdapter.forJRE()
                             .getCollatorProvider().getInstance(desiredLocale);
            }
            while (true) {
                if (ref != null) {
                    // Remove the empty SoftReference if any
                    cache.remove(desiredLocale, ref);
                }
                ref = cache.putIfAbsent(desiredLocale, new SoftReference<>(result));
                if (ref == null) {
                    break;
                }
                Collator cachedColl = ref.get();
                if (cachedColl != null) {
                    result = cachedColl;
                    break;
                }
            }
        }
        return (Collator) result.clone(); // make the world safe
    }

    /**
     * Compares the source string to the target string according to the
     * collation rules for this Collator.  Returns an integer less than,
     * equal to or greater than zero depending on whether the source String is
     * less than, equal to or greater than the target string.  See the Collator
     * class description for an example of use.
     * <p>
     * For a one time comparison, this method has the best performance. If a
     * given String will be involved in multiple comparisons, CollationKey.compareTo
     * has the best performance. See the Collator class description for an example
     * using CollationKeys.
     * @param source the source string.
     * @param target the target string.
     * @return Returns an integer value. Value is less than zero if source is less than
     * target, value is zero if source and target are equal, value is greater than zero
     * if source is greater than target.
     * @see java.text.CollationKey
     * @see java.text.Collator#getCollationKey
     */
    public abstract int compare(String source, String target);

    /**
     * Compares its two arguments for order.  Returns a negative integer,
     * zero, or a positive integer as the first argument is less than, equal
     * to, or greater than the second.
     * <p>
     * This implementation merely returns
     *  {@code  compare((String)o1, (String)o2) }.
     *
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @throws    ClassCastException the arguments cannot be cast to Strings.
     * @see java.util.Comparator
     * @since   1.2
     */
    @Override
    public int compare(Object o1, Object o2) {
    return compare((String)o1, (String)o2);
    }

    /**
     * Transforms the String into a series of bits that can be compared bitwise
     * to other CollationKeys. CollationKeys provide better performance than
     * Collator.compare when Strings are involved in multiple comparisons.
     * See the Collator class description for an example using CollationKeys.
     * @param source the string to be transformed into a collation key.
     * @return the CollationKey for the given String based on this Collator's collation
     * rules. If the source String is null, a null CollationKey is returned.
     * @see java.text.CollationKey
     * @see java.text.Collator#compare
     */
    public abstract CollationKey getCollationKey(String source);

    /**
     * Convenience method for comparing the equality of two strings based on
     * this Collator's collation rules.
     * @param source the source string to be compared with.
     * @param target the target string to be compared with.
     * @return true if the strings are equal according to the collation
     * rules.  false, otherwise.
     * @see java.text.Collator#compare
     */
    public boolean equals(String source, String target)
    {
        return (compare(source, target) == Collator.EQUAL);
    }

    /**
     * Returns this Collator's strength property.  The strength property determines
     * the minimum level of difference considered significant during comparison.
     * See the Collator class description for an example of use.
     * @return this Collator's current strength property.
     * @see java.text.Collator#setStrength
     * @see java.text.Collator#PRIMARY
     * @see java.text.Collator#SECONDARY
     * @see java.text.Collator#TERTIARY
     * @see java.text.Collator#IDENTICAL
     */
    public synchronized int getStrength()
    {
        return strength;
    }

    /**
     * Sets this Collator's strength property.  The strength property determines
     * the minimum level of difference considered significant during comparison.
     * See the Collator class description for an example of use.
     * @param newStrength  the new strength value.
     * @see java.text.Collator#getStrength
     * @see java.text.Collator#PRIMARY
     * @see java.text.Collator#SECONDARY
     * @see java.text.Collator#TERTIARY
     * @see java.text.Collator#IDENTICAL
     * @throws     IllegalArgumentException If the new strength value is not one of
     * PRIMARY, SECONDARY, TERTIARY or IDENTICAL.
     */
    public synchronized void setStrength(int newStrength) {
        if ((newStrength != PRIMARY) &&
            (newStrength != SECONDARY) &&
            (newStrength != TERTIARY) &&
            (newStrength != IDENTICAL)) {
            throw new IllegalArgumentException("Incorrect comparison level.");
        }
        strength = newStrength;
    }

    /**
     * Get the decomposition mode of this Collator. Decomposition mode
     * determines how Unicode composed characters are handled. Adjusting
     * decomposition mode allows the user to select between faster and more
     * complete collation behavior.
     * <p>The three values for decomposition mode are:
     * <UL>
     * <LI>NO_DECOMPOSITION,
     * <LI>CANONICAL_DECOMPOSITION
     * <LI>FULL_DECOMPOSITION.
     * </UL>
     * See the documentation for these three constants for a description
     * of their meaning.
     * @return the decomposition mode
     * @see java.text.Collator#setDecomposition
     * @see java.text.Collator#NO_DECOMPOSITION
     * @see java.text.Collator#CANONICAL_DECOMPOSITION
     * @see java.text.Collator#FULL_DECOMPOSITION
     */
    public synchronized int getDecomposition()
    {
        return decmp;
    }
    /**
     * Set the decomposition mode of this Collator. See getDecomposition
     * for a description of decomposition mode.
     * @param decompositionMode  the new decomposition mode.
     * @see java.text.Collator#getDecomposition
     * @see java.text.Collator#NO_DECOMPOSITION
     * @see java.text.Collator#CANONICAL_DECOMPOSITION
     * @see java.text.Collator#FULL_DECOMPOSITION
     * @throws    IllegalArgumentException If the given value is not a valid decomposition
     * mode.
     */
    public synchronized void setDecomposition(int decompositionMode) {
        if ((decompositionMode != NO_DECOMPOSITION) &&
            (decompositionMode != CANONICAL_DECOMPOSITION) &&
            (decompositionMode != FULL_DECOMPOSITION)) {
            throw new IllegalArgumentException("Wrong decomposition mode.");
        }
        decmp = decompositionMode;
    }

    /**
     * Returns an array of all locales for which the
     * {@code getInstance} methods of this class can return
     * localized instances.
     * The returned array represents the union of locales supported
     * by the Java runtime and by installed
     * {@link java.text.spi.CollatorProvider CollatorProvider} implementations.
     * It must contain at least a Locale instance equal to
     * {@link java.util.Locale#US Locale.US}.
     *
     * @return An array of locales for which localized
     *         {@code Collator} instances are available.
     */
    public static synchronized Locale[] getAvailableLocales() {
        LocaleServiceProviderPool pool =
            LocaleServiceProviderPool.getPool(CollatorProvider.class);
        return pool.getAvailableLocales();
    }

    /**
     * Overrides Cloneable
     */
    @Override
    public Object clone()
    {
        try {
            return (Collator)super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }

    /**
     * Compares the equality of two Collators.
     * @param that the Collator to be compared with this.
     * @return true if this Collator is the same as that Collator;
     * false otherwise.
     */
    @Override
    public boolean equals(Object that)
    {
        if (this == that) {
            return true;
        }
        if (that == null) {
            return false;
        }
        if (getClass() != that.getClass()) {
            return false;
        }
        Collator other = (Collator) that;
        return ((strength == other.strength) &&
                (decmp == other.decmp));
    }

    /**
     * Generates the hash code for this Collator.
     */
    @Override
    public abstract int hashCode();

    /**
     * Default constructor.  This constructor is
     * protected so subclasses can get access to it. Users typically create
     * a Collator sub-class by calling the factory method getInstance.
     * @see java.text.Collator#getInstance
     */
    protected Collator()
    {
        strength = TERTIARY;
        decmp = CANONICAL_DECOMPOSITION;
    }

    private int strength = 0;
    private int decmp = 0;
    private static final ConcurrentMap<Locale, SoftReference<Collator>> cache
            = new ConcurrentHashMap<>();

    //
    // FIXME: These three constants should be removed.
    //
    /**
     * LESS is returned if source string is compared to be less than target
     * string in the compare() method.
     * @see java.text.Collator#compare
     */
    static final int LESS = -1;
    /**
     * EQUAL is returned if source string is compared to be equal to target
     * string in the compare() method.
     * @see java.text.Collator#compare
     */
    static final int EQUAL = 0;
    /**
     * GREATER is returned if source string is compared to be greater than
     * target string in the compare() method.
     * @see java.text.Collator#compare
     */
    static final int GREATER = 1;
 }