Combinations java in a pgm

Combinations.java

public class Combinations

{

              public static void comb1(String s)

             {

                  comb1("", s);

              }

    private static void comb1(String prefix, String s)

     {

        if (s.length() > 0)

         {

            System.out.println(prefix + s.charAt(0));

            comb1(prefix + s.charAt(0), s.substring(1));

            comb1(prefix,               s.substring(1));

        }

    } 

                 public static void comb2(String s)

                 {

                      comb2("", s);

                  }

    private static void comb2(String prefix, String s)

    {

        System.out.println(prefix);

        for (int i = 0; i < s.length(); i++)

            comb2(prefix + s.charAt(i), s.substring(i + 1));

    } 

    public static void main(String[] args)

    {

       int N = Integer.parseInt(args[0]);

                    String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

       String elements = alphabet.substring(0, N);

       comb1(elements);

       System.out.println();

                    comb2(elements);

       System.out.println();

    }

}