Example code for a Stack Overflow comment: https://stackoverflow.com/a/64549281/1509433

Anagrams.java

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Anagrams {
    public static List<String> anagrams(String s) {
        List<String> output = new ArrayList<String>();
        if (s.length() == 0)
            return output;
        if (s.length() == 1) {
            output.add(s);
            return output;
        }
        Set<String> prefixes = new HashSet<String>();
        for (int i = 0; i < s.length(); ++i) {
            String c = s.substring(i, i + 1);
            // Skip generating repeated anagrams
            if (prefixes.contains(c))
                continue;
            prefixes.add(c);
            // Remove char c from string s to form string s2
            String s2 = s.substring(0, i) + s.substring(i + 1);
            // Calculate anagrams of s2 and append each to char c
            List<String> anagrams2 = anagrams(s2);
            for (String anagram : anagrams2) {
                output.add(c + anagram);
            }
        }
        return output;
    }
    
    public static void main(String[] args) {
        List<String> l = anagrams("abb");
        for (String s : l) {
            System.out.println(s);  // abb, bab, bba
        }
    }
}