libjava/classpath/java/util/spi/LocaleServiceProvider.java

/* LocaleServiceProvider.java -- Superclass of locale SPIs
   Copyright (C) 2007 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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permission to link this library with independent modules to produce an
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package java.util.spi;

import java.util.Locale;

/**
 * <p>
 * This is the superclass of all the {@link Locale} service
 * provider interfaces or SPIs.  The locale SPIs are used
 * to allow for the provision of additional support for
 * locale-specific data.  The runtime environment has its
 * own collection of locale data, but these interfaces allow
 * this to be extended by external classes.
 * </p>
 * <p>
 * Service providers are created as concrete implementations
 * of these interfaces, and accessed using the extension
 * mechanism, realised by {@link ServiceLoader}.  When a factory
 * method of one of the locale-specific classes (such as
 * {@link java.text.DateFormatSymbols} or {@link java.util.Currency})
 * is called, the runtime environment is first asked to
 * provide data for the specified locale.  If the runtime
 * environment fails to provide this, then the offer is
 * made to service providers which implement the appropriate
 * interface.
 * </p>
 * <p>
 * Each provider implements the method specified by this
 * class, {@link #getAvailableLocales()}.  This method is
 * called first to determine whether the provider will be of
 * any use in providing data for the specified locale.  If
 * a provider is found to be capable, then a more specific
 * method appropriate to the class requiring the data will
 * be called.  In the case of {@link java.text.DateFormatSymbols},
 * this would be
 * {@link java.text.spi.DateFormatSymbols#getInstance(Locale)}.
 * </p>
 * <p>
 * If neither a service provider nor the runtime environment
 * itself can fulfill the request, a fallback procedure is
 * engaged.  The locale is modified by applying the first
 * applicable rule:
 * </p>
 * <ol>
 * <li>If the variant contains a <code>'_'</code>, then
 * this and everything following it is trimmed.</li>
 * <li>If the variant is non-empty, it is converted to
 * an empty string.</li>
 * <li>If the country is non-empty, it is converted to
 * an empty string.</li>
 * <li>If the language is non-empty, it is converted to
 * an empty string.</li>
 * </ol>
 * <p>
 * The modified locale is then used to start the same
 * process again.  The root locale (@link java.util.Locale#ROOT}
 * must be supported by the runtime environment in order
 * to terminate this cycle.
 * </p>
 * <p>
 * Note that any names returned by the providers may
 * be <code>null</code>.  Returning a <code>null</code>
 * name is considered equivalent to not supporting a
 * particular locale.
 * </p>
 *
 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
 * @since 1.6
 */
public abstract class LocaleServiceProvider
{

  /**
   * Constructs a new {@link LocaleServiceProvider}.
   * Provided for implicit invocation by subclasses.
   */
  protected LocaleServiceProvider()
  {
  }

  /**
   * Returns an array of {@link Locale} instances,
   * for which the provider can supply localized data.
   *
   * @return an array of supported locales.
   */
  public abstract Locale[] getAvailableLocales();

}