Permutations java in a pgm

Permutations.java

public class Permutations

{

              public  static void perm1(String s)

              {

                   perm1("", s);

              }

    private static void perm1(String prefix, String s)

     {

        int N = s.length();

        if (N == 0) System.out.println(prefix);

        else

           {

            for (int i = 0; i < N; i++)

               perm1(prefix + s.charAt(i), s.substring(0, i) + s.substring(i+1, N));

        }

    }

    public static void perm2(String s)

    {

       int N = s.length();

       char[] a = new char[N];

       for (int i = 0; i < N; i++)

           a[i] = s.charAt(i);

       perm2(a, N);

    }

                  private static void perm2(char[] a, int n)

  {

        if (n == 1)

       {

            System.out.println(a);

            return;

        }

        for (int i = 0; i < n; i++)

        {

            swap(a, i, n-1);

            perm2(a, n-1);

            swap(a, i, n-1);

        }

    } 

                 private static void swap(char[] a, int i, int j)

                 {

        char c;

        c = a[i]; a[i] = a[j]; a[j] = c;

    }

                 public static void main(String[] args)

                 {

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

                    String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

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

       perm1(elements);

       System.out.println();

       perm2(elements);

    }

}