!instanceof - how can i get this logic to work...because it doesnt

Question

So I'm working with S Linked Lists and theres an add(E object) method that we are creating.
So its supposed to first check-well at least at some point in the method- that the object being passed in is of the same type as my SLL. If its not im supposed to throw a new ClassCastException.
I tried this at the beginning of the method:
public void add(E obj) throws ClassCastException
         if(obj !instanceof Doctor) throw new ClassCastException();
         Doctor d = (Doctor)obj;
         int index = 0;
         MySLLNode<E> item = head;
         for(int i = 0; i<size(); i++) {
              if (d.compareTo(item.getData()) < 0) {
                   super.add(index,obj);
                   size++;
                   break;
              if (d.compareTo(item.getData()) == 0) {
                   super.add(index+1,obj);
                   size++;
                   break;
              else {
                   index++;
                   item = item.next;
         addLast(obj);
         size++;
    }.....but im getting a couple of errors
./MySortedSLL.java:42: ')' expected
         if(obj !instanceof Doctor) throw new ClassCastException();
               ^
./MySortedSLL.java:42: illegal start of expression
         if(obj !instanceof Doctor) throw new ClassCastException();
                 ^
./MySortedSLL.java:42: ';' expected
         if(obj !instanceof Doctor) throw new ClassCastException();
                                  ^So is there a better way to check that the object being passed in (which wants to be added to my SLL) is of compatable type...being that it is of type Doctor?
Thanks in advance....

Answer 1

Rather than
      if (f !instanceof Fubar) {
         System.out.println("Yeah!");
      }try
      if (!(f instanceof Fubar)) {
         System.out.println("Rah!");
      }