// steps to do to construct an object, where the id is the object to be built
public class ConstructionSteps extends ToDoList {
   public String toString() {
      String result = "Steps to build " + getId() + ":\n";
      for(int i = 0; i < this.size(); ++i)
         result = "  " + (i + 1) + ". " + this.get(i) + "\n";
      return result;
   }
}