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/*
 * (C) Copyright Taligent, Inc. 1996-1998 -  All Rights Reserved
 * (C) Copyright IBM Corp. 1996-1998 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

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 Collator class performs locale-sensitive
String comparison. You use this class to build
searching and sorting routines for natural language text.

Collator is an abstract base class. Subclasses
implement specific collation strategies. One subclass,
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.

Like other locale-sensitive classes, you can use the static
factory method, getInstance, to obtain the appropriate
Collator object for a given locale. You will only need
to look at the subclasses of Collator if you need
to understand the details of a particular collation strategy or
if you need to modify that strategy.

The following example shows how to compare two strings using
the Collator for the default locale.


// 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");



You can set a Collator's strength property
to determine the level of difference considered significant in
comparisons. Four strengths are provided: PRIMARY,
SECONDARY, TERTIARY, and 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 "ě" 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.

//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");
}



For comparing Strings exactly once, the compare
method provides the best performance. When sorting a list of
Strings however, it is generally necessary to compare each
String multiple times. In this case, CollationKeys
provide better performance. The CollationKey class converts
a String to a series of bits that can be compared bitwise
against other CollationKeys. A CollationKey is
created by a Collator object for a given String.


Note: CollationKeys from different
Collators can not be compared. See the class description for CollationKey for an example using CollationKeys.
Author:
     Helena Shih, Laura Werner, Richard Gillam
See Also:
RuleBasedCollator
CollationKey
CollationElementIterator
Locale
Since:
1.1/**
 * The <code>Collator</code> class performs locale-sensitive
 * <code>String</code> comparison. You use this class to build
 * searching and sorting routines for natural language text.
 *
 * <p>
 * <code>Collator</code> is an abstract base class. Subclasses
 * implement specific collation strategies. One subclass,
 * <code>RuleBasedCollator</code>, 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</code>, to obtain the appropriate
 * <code>Collator</code> object for a given locale. You will only need
 * to look at the subclasses of <code>Collator</code> 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</code> 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</code>'s <em>strength</em> property
 * to determine the level of difference considered significant in
 * comparisons. Four strengths are provided: <code>PRIMARY</code>,
 * <code>SECONDARY</code>, <code>TERTIARY</code>, and <code>IDENTICAL</code>.
 * 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</code>s exactly once, the <code>compare</code>
 * method provides the best performance. When sorting a list of
 * <code>String</code>s however, it is generally necessary to compare each
 * <code>String</code> multiple times. In this case, <code>CollationKey</code>s
 * provide better performance. The <code>CollationKey</code> class converts
 * a <code>String</code> to a series of bits that can be compared bitwise
 * against other <code>CollationKey</code>s. A <code>CollationKey</code> is
 * created by a <code>Collator</code> object for a given <code>String</code>.
 * <br>
 * <strong>Note:</strong> <code>CollationKey</code>s from different
 * <code>Collator</code>s can not be compared. See the class description
 * for {@link CollationKey}
 * for an example using <code>CollationKey</code>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 Also:
setStrength.setStrength
getStrength/**
     * 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 Also:
setStrength.setStrength
getStrength/**
     * 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 Also:
setStrength.setStrength
getStrength/**
     * 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 ("\u0001" vs "\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
"\u00C0" (A-grave) and combining accents such as "A\u0300"
(A, combining-grave) will be considered significant at the IDENTICAL
level if decomposition is set to NO_DECOMPOSITION.
/**
     * 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 Also:
getDecomposition.getDecomposition
setDecomposition/**
     * 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.

CANONICAL_DECOMPOSITION corresponds to Normalization Form D as
described in
Unicode
Technical Report #15.
See Also:
getDecomposition.getDecomposition
setDecomposition/**
     * 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/unicode/reports/tr15/tr15-23.html">Unicode
     * Technical Report #15</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.

FULL_DECOMPOSITION corresponds to Normalization Form KD as
described in
Unicode
Technical Report #15.
See Also:
getDecomposition.getDecomposition
setDecomposition/**
     * 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/unicode/reports/tr15/tr15-23.html">Unicode
     * Technical Report #15</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.
See Also:
Locale.getDefault
Returns:
the Collator for the default locale.(for example, en_US)/**
     * 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.
Params:
desiredLocale – the desired locale.
See Also:
Locale
ResourceBundle
Returns:
the Collator for the desired locale./**
     * 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.

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.
Params:
source – the source string.
target – the target string.
See Also:
CollationKey
getCollationKey
Returns:
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./**
     * 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.

This implementation merely returns
  compare((String)o1, (String)o2) .
Throws:
ClassCastException – the arguments cannot be cast to Strings.
See Also:
Comparator
Returns:
a negative integer, zero, or a positive integer as the
        first argument is less than, equal to, or greater than the
        second.
Since:
  1.2/**
     * 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) </code>.
     *
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @exception 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.
Params:
source – the string to be transformed into a collation key.
See Also:
CollationKey
compare
Returns:
the CollationKey for the given String based on this Collator's collation
rules. If the source String is null, a null CollationKey is returned./**
     * 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.
Params:
source – the source string to be compared with.
target – the target string to be compared with.
See Also:
compare
Returns:
true if the strings are equal according to the collation
rules.  false, otherwise./**
     * 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.
See Also:
setStrength
PRIMARY
SECONDARY
TERTIARY
IDENTICAL
Returns:
this Collator's current strength property./**
     * 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.
Params:
newStrength –  the new strength value.
Throws:
IllegalArgumentException – If the new strength value is not one of
PRIMARY, SECONDARY, TERTIARY or IDENTICAL.
See Also:
getStrength
PRIMARY
SECONDARY
TERTIARY
IDENTICAL/**
     * 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
     * @exception  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.
The three values for decomposition mode are:

NO_DECOMPOSITION,
CANONICAL_DECOMPOSITION
FULL_DECOMPOSITION.

See the documentation for these three constants for a description
of their meaning.
See Also:
setDecomposition
NO_DECOMPOSITION
CANONICAL_DECOMPOSITION
FULL_DECOMPOSITION
Returns:
the decomposition mode/**
     * 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.
Params:
decompositionMode –  the new decomposition mode.
Throws:
IllegalArgumentException – If the given value is not a valid decomposition
mode.
See Also:
getDecomposition
NO_DECOMPOSITION
CANONICAL_DECOMPOSITION
FULL_DECOMPOSITION/**
     * 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
     * @exception 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
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 CollatorProvider implementations. It must contain at least a Locale instance equal to Locale.US. 
Returns:
An array of locales for which localized
        Collator instances are available./**
     * Returns an array of all locales for which the
     * <code>getInstance</code> 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</code> instances are available.
     */
    public static synchronized Locale[] getAvailableLocales() {
        LocaleServiceProviderPool pool =
            LocaleServiceProviderPool.getPool(CollatorProvider.class);
        return pool.getAvailableLocales();
    }

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

    
Compares the equality of two Collators.
Params:
that – the Collator to be compared with this.
Returns:
true if this Collator is the same as that Collator;
false otherwise./**
     * 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.
/**
     * 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 Also:
getInstance.getInstance/**
     * 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 Also:
compare.compare/**
     * 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 Also:
compare.compare/**
     * 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 Also:
compare.compare/**
     * 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;
 }