单选题 {若有下面程序代码:public class Demo {public static void main(String[] args) {HashSet<String> set = new HashSet<String>();set.add("Tom");set.add("John");set.add("Tom");Iterator it = set.iterator();while(it.hasNext()){Object obj = it.next();System.out.print(obj);}}}则程序运行结果是( )}