Natural Order Numerical Sorting

import java.util.*;

void setup() {

  ArrayList<String> list = new ArrayList<String>();
  list.add("img10.jpg");
  list.add("img20.jpg");
  list.add("img1.jpg");
  list.add("img2.jpg");

  Collections.sort(list, new AlphaNumericSorter() );
  println( list );
}

void draw() {

}

// Code from http://stackoverflow.com/questions/1262239/natural-sort-order-string-comparison-in-java-is-one-built-in
/**
 * Sorter that compares the given Alpha-numeric strings. This iterates through each characters to
 * decide the sort order. There are 3 possible cases while iterating,
 *
 * <li>If both have same non-digit characters then the consecutive characters will be considered for
 * comparison.</li>
 *
 * <li>If both have numbers at the same position (with/without non-digit characters) the consecutive
 * digit characters will be considered to form the valid integer representation of the characters
 * will be taken and compared.</li>
 *
 * <li>At any point if the comparison gives the order(either > or <) then the consecutive characters
 * will not be considered.</li>
 *
 * For ex., this will be the ordered O/P of the given list of Strings.(The bold characters decides
 * its order) <i><b>2</b>b,<b>100</b>b,a<b>1</b>,A<b>2</b>y,a<b>100</b>,</i>
 *
 * @author kannan_r
 *
 */
class AlphaNumericSorter implements Comparator<String>
{
    /**
     * Does the Alphanumeric sort of the given two string
     */
    public int compare(String theStr1, String theStr2)
    {
        char[] theCharArr1 = theStr1.toCharArray();
        char[] theCharArr2 = theStr2.toCharArray();
        int aPosition = 0;
        if (Character.isDigit(theCharArr1[aPosition]) && Character.isDigit(theCharArr2[aPosition]))
        {
            return sortAsNumber(theCharArr1, theCharArr2, aPosition++ );
        }
        return sortAsString(theCharArr1, theCharArr2, 0);
    }

    /**
     * Sort the given Arrays as string starting from the given position. This will be a simple case
     * insensitive sort of each characters. But at any given position if there are digits in both
     * arrays then the method sortAsNumber will be invoked for the given position.
     *
     * @param theArray1 The first character array.
     * @param theArray2 The second character array.
     * @param thePosition The position starting from which the calculation will be done.
     * @return positive number when the Array1 is greater than Array2<br/>
     *         negative number when the Array2 is greater than Array1<br/>
     *         zero when the Array1 is equal to Array2
     */
    private int sortAsString(char[] theArray1, char[] theArray2, int thePosition)
    {
        int aResult = 0;
        if (thePosition < theArray1.length && thePosition < theArray2.length)
        {
            aResult = (int)theArray1[thePosition] - (int)theArray2[thePosition];
            if (aResult == 0)
            {
                ++thePosition;
                if (thePosition < theArray1.length && thePosition < theArray2.length)
                {
                    if (Character.isDigit(theArray1[thePosition]) && Character.isDigit(theArray2[thePosition]))
                    {
                        aResult = sortAsNumber(theArray1, theArray2, thePosition);
                    }
                    else
                    {
                        aResult = sortAsString(theArray1, theArray2, thePosition);
                    }
                }
            }
        }
        else
        {
            aResult = theArray1.length - theArray2.length;
        }
        return aResult;
    }

    /**
     * Sorts the characters in the given array as number starting from the given position. When
     * sorted as numbers the consecutive characters starting from the given position upto the first
     * non-digit character will be considered.
     *
     * @param theArray1 The first character array.
     * @param theArray2 The second character array.
     * @param thePosition The position starting from which the calculation will be done.
     * @return positive number when the Array1 is greater than Array2<br/>
     *         negative number when the Array2 is greater than Array1<br/>
     *         zero when the Array1 is equal to Array2
     */
    private int sortAsNumber(char[] theArray1, char[] theArray2, int thePosition)
    {
        int aResult = 0;
        int aNumberInStr1;
        int aNumberInStr2;
        if (thePosition < theArray1.length && thePosition < theArray2.length)
        {
            if (Character.isDigit(theArray1[thePosition]) && Character.isDigit(theArray1[thePosition]))
            {
                aNumberInStr1 = getNumberInStr(theArray1, thePosition);
                aNumberInStr2 = getNumberInStr(theArray2, thePosition);

                aResult = aNumberInStr1 - aNumberInStr2;

                if (aResult == 0)
                {
                    thePosition = getNonDigitPosition(theArray1, thePosition);
                    if (thePosition != -1)
                    {
                        aResult = sortAsString(theArray1, theArray2, thePosition);
                    }
                }
            }
            else
            {
                aResult = sortAsString(theArray1, theArray2, ++thePosition);
            }
        }
        else
        {
            aResult = theArray1.length - theArray2.length;
        }
        return aResult;
    }

    /**
     * Gets the position of the non digit character in the given array starting from the given
     * position.
     *
     * @param theCharArr /the character array.
     * @param thePosition The position after which the array need to be checked for non-digit
     *        character.
     * @return The position of the first non-digit character in the array.
     */
    private int getNonDigitPosition(char[] theCharArr, int thePosition)
    {
        for (int i = thePosition; i < theCharArr.length; i++ )
        {
            if ( !Character.isDigit(theCharArr[i]))
            {
                return i;
            }
        }
        return -1;
    }

    /**
     * Gets the integer value of the number starting from the given position of the given array.
     *
     * @param theCharArray The character array.
     * @param thePosition The position form which the number need to be calculated.
     * @return The integer value of the number.
     */
    private int getNumberInStr(char[] theCharArray, int thePosition)
    {
        int aNumber = 0;
        for (int i = thePosition; i < theCharArray.length; i++ )
        {
            if(!Character.isDigit(theCharArray[i]))
            {
               return aNumber;
            }
            aNumber += aNumber * 10 + (theCharArray[i] - 48);
        }
        return aNumber;
    }
}