AlphanumComparator.java

/*
 * 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
 *
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */
package org.rzo.yajsw.wrapper;

import java.util.Comparator;

// TODO: Auto-generated Javadoc
/**
 * This is an updated version with enhancements made by Daniel Migowski, Andre
 * Bogus, and David Koelle
 * 
 * To convert to use Templates (Java 1.5+): - Change "implements Comparator" to
 * "implements Comparator<String>" - Change "compare(Object o1, Object o2)" to
 * "compare(String s1, String s2)" - Remove the type checking and casting in
 * compare().
 * 
 * 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
{

	/**
	 * Checks if is digit.
	 * 
	 * @param ch
	 *            the ch
	 * 
	 * @return true, if is digit
	 */
	private final boolean isDigit(char ch)
	{
		return ch >= 48 && ch <= 57;
	}

	/**
	 * Length of string is passed in for improved efficiency (only need to
	 * calculate it once) *.
	 * 
	 * @param s
	 *            the s
	 * @param slength
	 *            the slength
	 * @param marker
	 *            the marker
	 * 
	 * @return the chunk
	 */
	private final 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();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
	 */
	public int compare(Object o1, Object o2)
	{
		if (!(o1 instanceof String) || !(o2 instanceof String))
		{
			return 0;
		}
		String s1 = (String) o1;
		String s2 = (String) o2;

		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 = 0;
			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;
	}
}