SummingVisitorDJ {
// how to use:
// to sum all get_y() parts of type int belonging to class X
// change "Weight" to "X", change "get_i()" to "get_y()"
// Java does not support this parameterization
{{
  public void start() { total=0; System.out.println("begin"); }
  public void before(Weight o) { 
    System.out.println("sum: add " + o.get_i() );
    total += o.get_i(); }
  public Object getReturnValue() {return new Integer(total);}
}}
}