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• AlphanumComparator.java

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net.sf.mpxj.common.AlphanumComparator Maven / Gradle / Ivy

package net.sf.mpxj.common;

/*
 * The Alphanum Algorithm is an improved sorting algorithm for strings
 * containing numbers.  Instead of sorting numbers in ASCII order like
 * a standard sort, this algorithm sorts numbers in numeric order.
 *
 * The Alphanum Algorithm is discussed at http://www.DaveKoelle.com
 *
 * Released under the MIT License - https://opensource.org/licenses/MIT
 *
 * Copyright 2007-2017 David Koelle
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

import java.util.Comparator;

/**
 * This is an updated version with enhancements made by Daniel Migowski,
 * Andre Bogus, and David Koelle. Updated by David Koelle in 2017.
 *
 * To use this class:
 *   Use the static "sort" method from the java.util.Collections class:
 *   Collections.sort(your list, new AlphanumComparator());
 */
public class AlphanumComparator implements Comparator
{
   /**
    * Determine if character is a digit.
    *
    * @param ch character to test.
    * @return true if character is a digit
    */
   private boolean isDigit(char ch)
   {
      return ((ch >= 48) && (ch <= 57));
   }

   /**
    * Retrieve the next chunk for comparison.
    * Note that the length of string is passed in for improved efficiency
    * (only need to calculate it once)
    *
    * @param s source string
    * @param slength source string length
    * @param marker current marker
    * @return next chunk
    */
   private String getChunk(String s, int slength, int marker)
   {
      StringBuilder chunk = new StringBuilder();
      char c = s.charAt(marker);
      chunk.append(c);
      marker++;
      if (isDigit(c))
      {
         while (marker < slength)
         {
            c = s.charAt(marker);
            if (!isDigit(c))
            {
               break;
            }
            chunk.append(c);
            marker++;
         }
      }
      else
      {
         while (marker < slength)
         {
            c = s.charAt(marker);
            if (isDigit(c))
            {
               break;
            }
            chunk.append(c);
            marker++;
         }
      }
      return chunk.toString();
   }

   @Override public int compare(String s1, String s2)
   {
      if ((s1 == null) || (s2 == null))
      {
         return 0;
      }

      int thisMarker = 0;
      int thatMarker = 0;
      int s1Length = s1.length();
      int s2Length = s2.length();

      while (thisMarker < s1Length && thatMarker < s2Length)
      {
         String thisChunk = getChunk(s1, s1Length, thisMarker);
         thisMarker += thisChunk.length();

         String thatChunk = getChunk(s2, s2Length, thatMarker);
         thatMarker += thatChunk.length();

         // If both chunks contain numeric characters, sort them numerically
         int result;
         if (isDigit(thisChunk.charAt(0)) && isDigit(thatChunk.charAt(0)))
         {
            // Simple chunk comparison by length.
            int thisChunkLength = thisChunk.length();
            result = thisChunkLength - thatChunk.length();
            // If equal, the first different number counts
            if (result == 0)
            {
               for (int i = 0; i < thisChunkLength; i++)
               {
                  result = thisChunk.charAt(i) - thatChunk.charAt(i);
                  if (result != 0)
                  {
                     return result;
                  }
               }
            }
         }
         else
         {
            result = thisChunk.compareTo(thatChunk);
         }

         if (result != 0)
         {
            return result;
         }
      }

      return s1Length - s2Length;
   }
}