leetcode--009 Linked List Cycle I

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