Strings aus char Array generieren

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.Set;

public class GenerateCombinations {

    public static String chars = "ABCDEFGH";  
    public static int anzahl = 2;
    
    public static void main(String Args){
        PermutationGenerator generator = new PermutationGenerator(chars,anzahl);
        ArrayList<String> permutations = generator.getPermutations();
        Set<String> s = new LinkedHashSet<String>(permutations);
        System.out.println(s);
    }
}
class PermutationGenerator {

    private String string;
    private ArrayList<String> permutations;
    private int MaxLengthOfFinalString;

    public PermutationGenerator(String string, int laenge) {
        this.string = string;
        this.permutations = new ArrayList<String>();
        this.MaxLengthOfFinalString = laenge;
    }

    public ArrayList<String> getPermutations() {
        permutation("", this.string);  
        return this.permutations;
    }

    private void permutation(String prefix, String str) {
        int n = str.length();
        if (n == 0) {
            this.permutations.add(prefix.substring(0,MaxLengthOfFinalString));
        } else {
            for (int i = 0; i < n; i++) {
                permutation(prefix + str.charAt(i), str.substring(0,i) + str.substring(i+1,n));
            }
        }
    }
}