Un Problema Común

class Milk {
  void drink() {
    System.out.println(You drink the milk.);
  }
}

class Oranges {
  void juggle() {
    System.out.println(You drop the oranges on the ground.);
  }
}

class Box {
  private Object contents;

  void add(Object thing) {
    if (contents == nulo) {
      contents = thing;
    } else {
      System.out.println(The box is full.);
    }
  }

  Object remove() {
    if (contents == nulo) {
      System.out.println(The box is empty.);
      return nulo;
    } else {
      Object thing = contents;
      contents = nulo;
      return thing;
    }
  }
}