给我举个用HashSet存储字母的例子

import java.util.HashSet;
import java.util.Iterator;
public class HashsetDemo{
public static void main(String[] args){
HashSet hash = new HashSet();
hash.add(\"a\");
hash.add(\"b\");
hash.add(\"c\");
Iterator it = hash.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
}
}