Generate list of all possible permutations of a string

Question

How would I go about generating a list of all possible permutations of a string between x and y characters in length, containing a variable list of characters.

Any l

Answer 1

import java.util.*;

public class all_subsets {
    public static void main(String[] args) {
        String a = "abcd";
        for(String s: all_perm(a)) {
            System.out.println(s);
        }
    }

    public static Set concat(String c, Set lst) {
        HashSet ret_set = new HashSet();
        for(String s: lst) {
            ret_set.add(c+s);
        }
        return ret_set;
    }

    public static HashSet all_perm(String a) {
        HashSet set = new HashSet();
        if(a.length() == 1) {
            set.add(a);
        } else {
            for(int i=0; i