java - 强制转换 List<> 覆盖 Java 中的内部类

Question

我有一个类，其中有一个我重写的内部类。看起来效果很好。

class Car {
   public static class CarItems
   {
      public void doStuff(){ ... }
   }
}

class Honda extends Car {
   public static class CarItems extends Car.CarItems
   {
      @Override
      public void doStuff(){ ... }
   }
}

问题

该 Car 类位于我也重写的另一个类中:

class Dealership {
   //
   // #1: Here's a list of stuff, which includes car items
   //     as defined in parent class
   //
   protected List<CarAndStuff> carsAndStuff;

   public static class CarsAndStuff {
      private List<CarItems> carItems;
      private String name;
      // ...

      //
      // #2: This only returns the items from the rest of the
      //     clutter in this class
      //
      public List<CarItems> getCarsItems() { return carsItems; }
   }

   // As defined above
   public static class CarItems { ... }
}

class HondaDealership extends Dealership {
   //
   // #3: This sub-class only cares about the items
   //
   protected List<CarItems> carItems;

   public void extractItemsFromParent() {
      List<CarItems> _items = new ArrayList<CarItems>();

      for(CarsAndStuff stuff : carsAndStuff) {
         //
         // #4: So I try to extract the items, but using my
         //     overriden method. ERROR!
         //
         carItems.addAll(carsAndStuff.getCarItems());
      }

      this.carItems = carItems;
   }

   // As defined above
   public static class CarItems extends Car.CarItems { ... }
}

希望这不是太多需要遵循的代码，而且这一切都非常简单......我得到的错误是在 #4 Java 正在尝试从 Car.CarItems 转换为本田.CarItems。它说:

The method addAll(Collection<? extends Honda.CarItems>)
  in the type List<Honda.CarItems> 
  is not applicable for the arguments (List<Car.CarItems>)

如果 Honda.CarItems 是 Car.CarItems，为什么它不允许我将列表添加到列表中？

Answer 1

这可能不是世界上最好的答案，但可以完成工作:

// Instead of addAll, add each item from CarsAndStuff.getCarItems
List<CarItems> _items = new ArrayList<CarItems>();

    for (CarsAndStuff stuff : carsAndStuff) {
        List<Car.CarItems> _carItems = stuff.getCarItems());
        for (CarItems _carItem: _carItems) {

            // ** Can't cast Car.CarItems ==> Honda.CarItems? Copy it! **
           _items.add(new CarItems(_carItem));

        }
    }

总之，无需从 Car.CarItems 强制转换(显式或隐式)到 Honda.CarItems，只需复制该对象，从而使其成为真正的 Honda.CarItems。这要求您的 Honda.CarItems 实现一个复制构造函数，这对您来说是一个额外的步骤:

class Honda extends Car {
  public static class CarItems extends Car.CarItems
  {

     public CarItems(Car.CarItems items) {
         this.property_1 = items.property_1;
         this.property_2 = items.property_2;
         this.property_3 = items.property_3;

         // etc.
     }

     @Override
     public void doStuff(){ ... }
  }
}