Algorithm matters? Well it depends...

import java.util.* ;

public class Test
{
	private final static char[] letters = {'A', 'B', 'C', 'D'} ;
	private final static int NB_CHOICES = letters.length ;
	private final static int LEN = 10 ;

	public Test()
	{
	}

	private static void add (char[] aWord, int anIndex, Collection allWords)
	{
		if (anIndex == LEN)
		{
			//allWords.add (new String (aWord)) ;	// Found a word
		}
		else
		{
			for (int i = 0; i < NB_CHOICES; i++)
			{
				aWord [anIndex] = letters [i] ;
				add (aWord, anIndex + 1, allWords) ;
			}
		}
	}

	public Collection algo1()
	{
		char[] buf = new char [LEN] ;

		Collection allWords = new ArrayList() ;

		add (buf, 0, allWords) ;

		return allWords ;
	}

	public Collection algo2()
	{
		Collection allWords = new ArrayList() ;

		char[] buf = new char [LEN] ;
		int[] steps = new int [LEN] ;
		int position = 0 ;

		do
		{
			int step = steps [position] ;

			if (step >= NB_CHOICES)
			{
				if (--position >= 0)
				{
					steps [position]++ ;
				}
			}
			else
			{
				buf [position] = letters [step] ;
				if ((position + 1) < LEN)
				{
					position++ ;
					steps [position] = 0 ;
				}
				else
				{
					//allWords.add (new String (buf)) ;	// Found a word
					steps [position]++ ;
				}
			}
		}
		while (position >= 0) ;

		return allWords ;
	}

	public static void main (String[] args)
	{
		Test test = new Test() ;

		long date1 = System.currentTimeMillis() ;
		Collection set1 = test.algo1() ;
		long date2 = System.currentTimeMillis() ;
		Collection set2 = test.algo2() ;
		long date3 = System.currentTimeMillis() ;
		System.out.println (date2 - date1) ;
		System.out.println (date3 - date2) ;
		System.out.println (set1.size()) ;
		System.out.println (set2.size()) ;
		System.out.println (set1.equals (set2)) ;
	}
}