import java.util.*;
public class MyClass {
public static void main(String args[]) {
Set<String> letters = new HashSet<>(Arrays.asList("a", "b", "c", "d", "a", "a"));
Iterator<String> it = letters.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
}
}
/*
run:
a
b
c
d
*/