Permutations and Permutations of size k, using recursion to implement

Permutation.java

public class Permutation
{
    public static void perm1(String s) { perm1("", s); }
    public 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 k)
    {
	perm2("", s, k);
    }
    public static void perm2(String prefix, String s, int k)
    {
	int N = prefix.length();

	int M = s.length();

	if(N == k) System.out.println(prefix);
	else
	    {
		for(int i = 0; i < M; i++)
		    perm2(prefix+s.charAt(i), s.substring(0, i) + s.substring(i+1, M), k);
	    }
    }
    public static void main(String[] args)
    {
	String alphabet = "abcdefghijklmnopqrstuvwxyz";
	int N = Integer.parseInt(args[0]);
	int K = Integer.parseInt(args[1]);
	String elements = alphabet.substring(0, N);
	perm2(elements, K);
    }
	
    
}