Check the object of whose instance it is in an HashSet

Question

Hi guys,
I have 2 subclasses.
I am adding instances of those classes in one HashSet.
But afterall i need to check how many instance found in this HashSet.
I tried to return data in an HashSet again. However returned HashSet has no element.
Student class inherited from Person class
--public static void main(String [] args){
          HashSet mySet = new HashSet();
          HashSet resultSet = new HashSet();
          Student s = new Student("Student1","1",new Date(12-12-2007));
          Teacher t = new Teacher("Teacher1","2",1.1);
          Teacher t1 = new Teacher("Teacher2","2",1.1);
          mySet.add(s);
          mySet.add(t);
          mySet.add(t1);
          resultSet = s.displayStudent(mySet); //here it stucks
public HashSet displayStudent(HashSet mySet){
          Iterator it = mySet.iterator();
          HashSet innerSet= new HashSet();
          innerSet = null;
          while (it.hasNext()) {
               if (it instanceof Student)  {
                    //System.out.println(getName());
                    //System.out.println(getAddress());
                    //System.out.println(getEntryDate());
                    innerSet.add(it);
                                it.next();
               else it.next();
          return innerSet;
     }

Answer 1

"it" is an Iterator and will never be instanceof Student. But the object returned by "it.next()" might be.