public A last(){
  A last=null;
  List<A> t=this;
  while (t.tail != null) {
    last=t.head;
    t=t.tail;
  }
  return last;
}

public A last ( ) { A last = null ; List < A > t = this ; while ( t . tail != null ) { last = t . head ; t = t . tail ; } return last ; }
the last element in the list , if any , or null .
