我有一个带有内部类的类,我可以重写它。这似乎很好。
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
Car类位于另一个我也要覆盖的类中:
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 { ... }
}
希望不需要太多代码,而且一切都非常简单……我得到的错误是,在
#4
上,Java试图将Car.CarItems转换为Honda.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 IS-A Car.CarItems,为什么不让我将List添加到List?
最佳答案
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,不是将Car.CarItems强制(显式或隐式)转换为Honda.CarItems,而是对其进行复制,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,这对您来说是额外的一步:
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(){ ... }
}
}