source: trunk/gcc/libjava/java/text/Collator.java

/* Collator.java -- Perform locale dependent String comparisons.
   Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.
 
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02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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exception statement from your version. */


package java.text;

import java.util.Locale;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import java.util.Comparator;

/**
 * This class is the abstract superclass of classes which perform 
 * locale dependent <code>String</code> comparisons.  A caller requests
 * an instance of <code>Collator</code> for a particular locale using
 * the <code>getInstance()</code> static method in this class.  That method
 * will return a locale specific subclass of <code>Collator</code> which
 * can be used to perform <code>String</code> comparisons for that locale.
 * If a subclass of <code>Collator</code> cannot be located for a particular
 * locale, a default instance for the current locale will be returned.  
 *
 * In addition to setting the correct locale, there are two additional
 * settings that can be adjusted to affect <code>String</code> comparisons:
 * strength and decomposition.  The strength value determines the level
 * of signficance of character differences required for them to sort
 * differently.  (For example, whether or not capital letters are considered
 * different from lower case letters).  The decomposition value affects how
 * variants of the same character are treated for sorting purposes.  (For
 * example, whether or not an accent is signficant or not).  These settings
 * are described in detail in the documentation for the methods and values
 * that are related to them.
 *
 * @author Tom Tromey <tromey@cygnus.com>
 * @author Aaron M. Renn (arenn@urbanophile.com)
 * @date March 18, 1999
 */
/* Written using "Java Class Libraries", 2nd edition, plus online
 * API docs for JDK 1.2 from http://www.javasoft.com.
 * Status: Mostly complete, but parts stubbed out.  Look for FIXME.
 */
public abstract class Collator implements Comparator, Cloneable
{
  /**
   * This constant is a strength value which indicates that only primary
   * differences between characters will be considered signficant.  As an
   * example, two completely different English letters such as 'a' and 'b'
   * are considered to have a primary difference.
   */
  public static final int PRIMARY = 0;
  
  /**
   * This constant is a strength value which indicates that only secondary
   * or primary differences between characters will be considered
   * significant.  An example of a secondary difference between characters
   * are instances of the same letter with different accented forms.
   */
  public static final int SECONDARY = 1;
  
  /**
   * This constant is a strength value which indicates that tertiary,
   * secondary, and primary differences will be considered during sorting.
   * An example of a tertiary difference is capitalization of a given letter.
   * This is the default value for the strength setting.
   */
  public static final int TERTIARY = 2;
  
  /**
   * This constant is a strength value which indicates that any difference
   * at all between character values are considered significant.
   */
  public static final int IDENTICAL = 3;
  
  /**
   * This constant indicates that accented characters won't be decomposed
   * when performing comparisons.  This will yield the fastest results, but
   * will only work correctly in call cases for languages which do not
   * use accents such as English.
   */
  public static final int NO_DECOMPOSITION = 0;
  
  /**
   * This constant indicates that only characters which are canonical variants
   * in Unicode 2.0 will be decomposed prior to performing comparisons.  This
   * will cause accented languages to be sorted correctly.  This is the
   * default decomposition value.
   */
  public static final int CANONICAL_DECOMPOSITION = 1;
  
  /**
   * This constant indicates that both canonical variants and compatibility
   * variants in Unicode 2.0 will be decomposed prior to performing
   * comparisons.  This is the slowest mode, but is required to get the
   * correct sorting for certain languages with certain special formats.
   */
  public static final int FULL_DECOMPOSITION = 2;

  /**
   * This method initializes a new instance of <code>Collator</code> to have
   * the default strength (TERTIARY) and decomposition 
   * (CANONICAL_DECOMPOSITION) settings.  This constructor is protected and
   * is for use by subclasses only.  Non-subclass callers should use the
   * static <code>getInstance()</code> methods of this class to instantiate
   * <code>Collation</code> objects for the desired locale.
   */
  protected Collator ()
  {
    strength = TERTIARY;
    decmp = CANONICAL_DECOMPOSITION;
  }

  /**
   * This method compares the two <code>String</code>'s and returns an
   * integer indicating whether or not the first argument is less than,
   * equal to, or greater than the second argument.  The comparison is
   * performed according to the rules of the locale for this 
   * <code>Collator</code> and the strength and decomposition rules in
   * effect.
   *
   * @param str1 The first object to compare
   * @param str2 The second object to compare
   *
   * @return A negative integer if str1 &lt; str2, 0 if str1 == str2, or
   * a positive integer if str1 &gt; str2. 
   */
  public abstract int compare (String source, String target);

  /**
   * This method compares the two <code>Object</code>'s and returns an
   * integer indicating whether or not the first argument is less than,
   * equal to, or greater than the second argument.  These two objects
   * must be <code>String</code>'s or an exception will be thrown.
   *
   * @param obj1 The first object to compare
   * @param obj2 The second object to compare
   *
   * @return A negative integer if obj1 &lt; obj2, 0 if obj1 == obj2, or
   * a positive integer if obj1 &gt; obj2. 
   *
   * @exception ClassCastException If the arguments are not instances
   * of <code>String</code>. 
   */
  public int compare (Object o1, Object o2)
  {
    return compare ((String) o1, (String) o2);
  }

  /**
   * This method tests the specified object for equality against this
   * object.  This will be true if and only if the following conditions are
   * met:
   * <ul>
   * <li>The specified object is not <code>null</code>.
   * <li>The specified object is an instance of <code>Collator</code>.
   * <li>The specified object has the same strength and decomposition
   * settings as this object.
   * </ul>
   *
   * @param obj The <code>Object</code> to test for equality against
   *            this object. 
   *
   * @return <code>true</code> if the specified object is equal to
   * this one, <code>false</code> otherwise.
   */
  public boolean equals (Object obj)
  {
    if (! (obj instanceof Collator))
      return false;
    Collator c = (Collator) obj;
    return decmp == c.decmp && strength == c.strength;
  }

  /**
   * This method tests whether the specified <code>String</code>'s are equal
   * according to the collation rules for the locale of this object and
   * the current strength and decomposition settings.
   *
   * @param str1 The first <code>String</code> to compare
   * @param str2 The second <code>String</code> to compare
   *
   * @return <code>true</code> if the two strings are equal,
   * <code>false</code> otherwise. 
   */
  public boolean equals (String source, String target)
  {
    return compare (source, target) == 0;
  }

  /**
   * This method returns a copy of this <code>Collator</code> object.
   *
   * @return A duplicate of this object.
   */
  public Object clone ()
  {
    try
      {
        return super.clone ();
      }
    catch (CloneNotSupportedException _)
      {
        return null;
      }
  }

  /**
   * This method returns an array of <code>Locale</code> objects which is
   * the list of locales for which <code>Collator</code> objects exist.
   *
   * @return The list of locales for which <code>Collator</code>'s exist.
   */
  public static synchronized Locale[] getAvailableLocales ()
  {
    // FIXME
    Locale[] l = new Locale[1];
    l[0] = Locale.US;
    return l;
  }

  /**
   * This method transforms the specified <code>String</code> into a
   * <code>CollationKey</code> for faster comparisons.  This is useful when
   * comparisons against a string might be performed multiple times, such
   * as during a sort operation.
   *
   * @param str The <code>String</code> to convert.
   *
   * @return A <code>CollationKey</code> for the specified <code>String</code>.
   */
  public abstract CollationKey getCollationKey (String source);

  /**
   * This method returns the current decomposition setting for this
   * object.  This * will be one of NO_DECOMPOSITION,
   * CANONICAL_DECOMPOSITION, or * FULL_DECOMPOSITION.  See the
   * documentation for those constants for an * explanation of this
   * setting.
   *
   * @return The current decomposition setting.
   */
  public synchronized int getDecomposition ()
  {
    return decmp;
  }

  /**
   * This method returns an instance of <code>Collator</code> for the
   * default locale.
   *
   * @return A <code>Collator</code> for the default locale.
   */
  public static Collator getInstance ()
  {
    return getInstance (Locale.getDefault());
  }

  /**
   * This method returns an instance of <code>Collator</code> for the
   * specified locale.  If no <code>Collator</code> exists for the desired
   * locale, a <code>Collator</code> for the default locale will be returned.
   *
   * @param locale The desired localed to load a <code>Collator</code> for.
   *
   * @return A <code>Collator</code> for the requested locale
   */
  public static Collator getInstance (Locale loc)
  {
    ResourceBundle res;
    String pattern;
    try
      {
        res = ResourceBundle.getBundle("gnu.java.locale.LocaleInformation",
                                       loc);
        pattern = res.getString("collation_rules");
      }
    catch (MissingResourceException x)
      {
        return null;
      }
    try
      {
        return new RuleBasedCollator (pattern);
      }
    catch (ParseException x)
      {
        return null;
      }
  }

  /**
   * This method returns the current strength setting for this object.  This
   * will be one of PRIMARY, SECONDARY, TERTIARY, or IDENTICAL.  See the
   * documentation for those constants for an explanation of this setting.
   *
   * @return The current strength setting.
   */
  public synchronized int getStrength ()
  {
    return strength;
  }

  /**
   * This method returns a hash code value for this object.
   *
   * @return A hash value for this object.
   */
  public abstract int hashCode ();

  /**
   * This method sets the decomposition setting for this object to the
   * specified value.  This must be one of NO_DECOMPOSITION,
   * CANONICAL_DECOMPOSITION, or FULL_DECOMPOSITION.  Otherwise an
   * exception will be thrown.  See the documentation for those
   * contants for an explanation of this setting.
   *
   * @param decmp The new decomposition setting.
   *
   * @exception IllegalArgumentException If the requested
   * decomposition setting is not valid.
   */
  public synchronized void setDecomposition (int mode)
  {
    if (mode != NO_DECOMPOSITION
        && mode != CANONICAL_DECOMPOSITION
        && mode != FULL_DECOMPOSITION)
      throw new IllegalArgumentException ();
    decmp = mode;
  }

  /**
   * This method sets the strength setting for this object to the specified
   * value.  This must be one of PRIMARY, SECONDARY, TERTIARY, or IDENTICAL.
   * Otherwise an exception is thrown. See the documentation for these
   * constants for an explanation of this setting.
   * 
   * @param strength The new strength setting.
   *
   * @exception IllegalArgumentException If the requested strength
   * setting value is not valid.
   */
  public synchronized void setStrength (int strength)
  {
    if (strength != PRIMARY && strength != SECONDARY
        && strength != TERTIARY && strength != IDENTICAL)
      throw new IllegalArgumentException ();
    this.strength = strength;
  }

  // Decompose a single character and append results to the buffer.
  native final void decomposeCharacter (char c, StringBuffer buf);

  /**
   * This is the current collation decomposition setting.
   */
  int decmp;

  /**
   * This is the current collation strength setting.
   */
  int strength;
}