abstract class Dog {
  protected String name;
  protected Dog(String name) { this.name = name; }
  abstract public void bark();
}

class Labrador extends Dog {
  public Labrador(String name) { super(name); }
  public void bark() { System.out.println(name + ": woof!"); }
}

class Dalmatian extends Dog {
  public Dalmatian(String name) { super(name); }
  public void bark() { System.out.println(name + ": weee-arrr-ooof!"); }
}

/** Standard singly linked list cell */
class ListCell {
  private final Object value;
  private final ListCell next;

  public ListCell(Object value, ListCell next) {
    this.value = value;
    this.next = next;
  }
  public Object getValue() { return value; }
  public ListCell next() { return next; }
}

public class Kennel {
  private ListCell dogs; // The head of the list
  public Kennel(ListCell dogs) { this.dogs = dogs; }

  public void rollCall() {
    for (ListCell cell = dogs; cell != null; cell = cell.next()) {
      Dog d = (Dog)cell.getValue();
      d.bark();
    }
  }

  public static void main(String[] args) {
    Dog rover = new Labrador("rover");
    Dog spots = new Dalmatian("spot");
    ListCell dogs = new ListCell(rover, new ListCell(spots, null));
    Kennel k = new Kennel(dogs);
    k.rollCall();
  }
}