Permutations java in a pgm

PermutationsK.java

public class PermutationsK 

{

              public static void choose(char[] a, int R) 

             { 

               enumerate(a, a.length, R); 

              }

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

   {

        if (r == 0) 

   {

            for (int i = n; i < a.length; i++)

                System.out.println(a[i]);

            System.out.println();

            return;

        }

        for (int i = 0; i < n; i++) 

       {

            swap(a, i, n-1);

            enumerate(a, n-1, r-1);

            swap(a, i, n-1);

         }

    }  

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

    {

        char temp = a[i];

        a[i] = a[j];

        a[j] = temp;

    }

                 public static void main(String[] args) 

                {

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

        int k = Integer.parseInt(args[1]);

                     String elements = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

        char[] a = new char[N];

        for (int i = 0; i < N; i++)

            a[i] = elements.charAt(i);

        choose(a, k);

    }

 }