001    /* LocaleServiceProvider.java -- Superclass of locale SPIs
002       Copyright (C) 2007 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.util.spi;
039    
040    import java.util.Locale;
041    
042    /**
043     * <p>
044     * This is the superclass of all the {@link Locale} service
045     * provider interfaces or SPIs.  The locale SPIs are used
046     * to allow for the provision of additional support for
047     * locale-specific data.  The runtime environment has its
048     * own collection of locale data, but these interfaces allow
049     * this to be extended by external classes.
050     * </p>
051     * <p>
052     * Service providers are created as concrete implementations
053     * of these interfaces, and accessed using the extension
054     * mechanism, realised by {@link ServiceLoader}.  When a factory
055     * method of one of the locale-specific classes (such as
056     * {@link java.text.DateFormatSymbols} or {@link java.util.Currency})
057     * is called, the runtime environment is first asked to
058     * provide data for the specified locale.  If the runtime
059     * environment fails to provide this, then the offer is
060     * made to service providers which implement the appropriate
061     * interface.
062     * </p>
063     * <p>
064     * Each provider implements the method specified by this
065     * class, {@link #getAvailableLocales()}.  This method is
066     * called first to determine whether the provider will be of
067     * any use in providing data for the specified locale.  If
068     * a provider is found to be capable, then a more specific
069     * method appropriate to the class requiring the data will
070     * be called.  In the case of {@link java.text.DateFormatSymbols},
071     * this would be
072     * {@link java.text.spi.DateFormatSymbols#getInstance(Locale)}.
073     * </p>
074     * <p>
075     * If neither a service provider nor the runtime environment
076     * itself can fulfill the request, a fallback procedure is
077     * engaged.  The locale is modified by applying the first
078     * applicable rule:
079     * </p>
080     * <ol>
081     * <li>If the variant contains a <code>'_'</code>, then
082     * this and everything following it is trimmed.</li>
083     * <li>If the variant is non-empty, it is converted to
084     * an empty string.</li>
085     * <li>If the country is non-empty, it is converted to
086     * an empty string.</li>
087     * <li>If the language is non-empty, it is converted to
088     * an empty string.</li>
089     * </ol>
090     * <p>
091     * The modified locale is then used to start the same
092     * process again.  The root locale (@link java.util.Locale#ROOT}
093     * must be supported by the runtime environment in order
094     * to terminate this cycle.
095     * </p>
096     * <p>
097     * Note that any names returned by the providers may
098     * be <code>null</code>.  Returning a <code>null</code>
099     * name is considered equivalent to not supporting a
100     * particular locale.
101     * </p>
102     *
103     * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
104     * @since 1.6
105     */
106    public abstract class LocaleServiceProvider
107    {
108    
109      /**
110       * Constructs a new {@link LocaleServiceProvider}.
111       * Provided for implicit invocation by subclasses.
112       */
113      protected LocaleServiceProvider()
114      {
115      }
116    
117      /**
118       * Returns an array of {@link Locale} instances,
119       * for which the provider can supply localized data.
120       *
121       * @return an array of supported locales.
122       */
123      public abstract Locale[] getAvailableLocales();
124    
125    }