import java.util.*;

class SetTest1{
    public static void main(String []args) {
        String string1= "ABFED";
        String string2= "AFBHI";

        Set<Character> set1 = string2CharSet(string1);
        set1.retainAll(string2CharSet(string2));
 
        System.out.println(set1.toString()); 
    }

    private static Set<Character> string2CharSet(String s1) {
        Set<Character> set1=new HashSet<Character>();
        Character[] cha1 = s1.chars().mapToObj(c -> (char) c).toArray(Character[]::new);
        set1.addAll(Arrays.asList(cha1));
        return set1;
    }

}