Linked List Cycle (java)

      public boolean hasCycle(ListNode head)
      {
          ListNode slow=head;
          ListNode fast=head;
          if(head==null)return false;
          while(fast.next!=null)
          {
              if(fast.next.next==null)return false;
              slow=slow.next;
              fast=fast.next.next;
              if(slow==fast)return true;
          }
          return false;

      }