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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
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   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
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   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  /*
   * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
   * (C) Copyright IBM Corp. 1996 - 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;
  
  /**
   * A <code>CollationKey</code> represents a <code>String</code> under the
   * rules of a specific <code>Collator</code> object. Comparing two
   * <code>CollationKey</code>s returns the relative order of the
   * <code>String</code>s they represent. Using <code>CollationKey</code>s
   * to compare <code>String</code>s is generally faster than using
   * <code>Collator.compare</code>. Thus, when the <code>String</code>s
   * must be compared multiple times, for example when sorting a list
   * of <code>String</code>s. It's more efficient to use <code>CollationKey</code>s.
   *
   * <p>
   * You can not create <code>CollationKey</code>s directly. Rather,
   * generate them by calling <code>Collator.getCollationKey</code>.
   * You can only compare <code>CollationKey</code>s generated from
   * the same <code>Collator</code> object.
   *
   * <p>
   * Generating a <code>CollationKey</code> for a <code>String</code>
   * involves examining the entire <code>String</code>
   * and converting it to series of bits that can be compared bitwise. This
   * allows fast comparisons once the keys are generated. The cost of generating
   * keys is recouped in faster comparisons when <code>String</code>s need
   * to be compared many times. On the other hand, the result of a comparison
   * is often determined by the first couple of characters of each <code>String</code>.
   * <code>Collator.compare</code> examines only as many characters as it needs which
   * allows it to be faster when doing single comparisons.
   * <p>
   * The following example shows how <code>CollationKey</code>s might be used
   * to sort a list of <code>String</code>s.
   * <blockquote>
   * <pre>{@code
   * // Create an array of CollationKeys for the Strings to be sorted.
   * Collator myCollator = Collator.getInstance();
   * CollationKey[] keys = new CollationKey[3];
   * keys[0] = myCollator.getCollationKey("Tom");
   * keys[1] = myCollator.getCollationKey("Dick");
   * keys[2] = myCollator.getCollationKey("Harry");
   * sort(keys);
   *
   * //...
   *
   * // Inside body of sort routine, compare keys this way
   * if (keys[i].compareTo(keys[j]) > 0)
   *    // swap keys[i] and keys[j]
   *
   * //...
   *
   * // Finally, when we've returned from sort.
   * System.out.println(keys[0].getSourceString());
   * System.out.println(keys[1].getSourceString());
   * System.out.println(keys[2].getSourceString());
   * }</pre>
   * </blockquote>
   *
   * @see          Collator
   * @see          RuleBasedCollator
   * @author       Helena Shih
   */
  
  public abstract class CollationKey implements Comparable<CollationKey> {
      /**
       * Compare this CollationKey to the target CollationKey. The collation rules of the
       * Collator object which created these keys are applied. <strong>Note:</strong>
       * CollationKeys created by different Collators can not be compared.
       * @param target target CollationKey
       * @return Returns an integer value. Value is less than zero if this is less
       * than target, value is zero if this and target are equal and value is greater than
       * zero if this is greater than target.
       * @see Collator#compare
       */
      abstract public int compareTo(CollationKey target);
  
      /**
       * Returns the String that this CollationKey represents.
       *
       * @return the source string of this CollationKey
       */
      public String getSourceString() {
          return source;
      }
  
  
      /**
       * Converts the CollationKey to a sequence of bits. If two CollationKeys
       * could be legitimately compared, then one could compare the byte arrays
       * for each of those keys to obtain the same result.  Byte arrays are
       * organized most significant byte first.
       *
       * @return a byte array representation of the CollationKey
       */
      abstract public byte[] toByteArray();
  
  
    /**
     * CollationKey constructor.
     *
     * @param source the source string
     * @exception NullPointerException if {@code source} is null
     * @since 1.6
     */
      protected CollationKey(String source) {
          if (source==null){
              throw new NullPointerException();
          }
          this.source = source;
      }
  
      final private String source;
  }
  