java子类问题
我有一个使用 BinaryTree 类构建的 BinarySearchTree 类。现在我想通过子类化 BinarySearchTree 类来构建一个 RedBlackTree 类。问题是 BinaryTree 类没有颜色字段。因此，我创建了一个 ColorBinaryTree 类，它是 BinaryTree 类的子类。这是我有点困惑的地方。在我的 BinaryTree 类中，我有以下方法
protected BinaryTree<E> parent(){
return parent;
}
，其中父级显然是另一个 BinaryTree 。在我的 RedBlackTree 类中，我还需要能够访问 ColorBinaryTree 对象的父对象。但是，我不能只使用从 BinaryTree 类继承的方法，因为它返回一个 BinaryTree 对象，这意味着我无法访问颜色。使用以下代码，我收到错误
ColorBinaryTree<E> parent = newNode.parent();
，其中 newNode 是 ColorBinaryTree 对象。所以在我看来，唯一的方法就是像这样覆盖我的 ColorBinaryTree 子类中的上述方法。
@Override
protected ColorBinaryTree<E> parent(){
return parent;
}
我是否缺少某种方法来获取此值，或者我是否只需要重写返回 BinaryTree 对象的所有方法？如果是这样，那似乎有点浪费，因为方法的主体完全相同。
I have a BinarySearchTree class which is built using a BinaryTree class. Now I want to build a RedBlackTree class by subclassing the BinarySearchTree class. The problem is that the BinaryTree class doesn't have a field for color. So, I created a ColorBinaryTree class that's a subclass of the BinaryTree class. Here's where I get a little confused. In my BinaryTree class I have the following method
protected BinaryTree<E> parent(){
return parent;
}
where parent is obviously another BinaryTree. In my RedBlackTree class, I will need to be able to access parents of ColorBinaryTree objects as well. However, I can't just use the method inherited from the BinaryTree class because that returns a BinaryTree object which means I can't access the color. With the following code I get an error
ColorBinaryTree<E> parent = newNode.parent();
where newNode is a ColorBinaryTree object. So it seems to me the only way to do it is to overwrite the above method in my ColorBinaryTree sublcass like so.
@Override
protected ColorBinaryTree<E> parent(){
return parent;
}
Am I missing some way to get aorund this or do I just have to go and override all of the methods that return BinaryTree objects? If so it seems kind of a waste since the body of the methods are exactly the same.
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评论（2）
是的，您应该执行协变覆盖。这并不是“浪费”，因为它限制了
ColorBinaryTree所有子类的parent返回类型。Yes, you should do the covariant overrides. This is not "a waste", since it constrains the return type of
parentfor all subclasses ofColorBinaryTree.您不转换超类父函数的结果是否有原因？
像这样：
也有点痛苦，但可能就是您正在寻找的。
处理它的最佳方法可能是使用返回 ColorBinaryTree 的方法覆盖返回 BinaryTree 的基类中的所有函数。然后在子类的实现中调用父类的方法并在返回之前执行强制转换。这样你的代码中就不会有一百万次的强制转换。它可能看起来像这样：
Is there a reason you're not casting the result of the superclass's parent function?
Like this:
Also kind of a pain, but probably what you're looking for.
The best way to deal with it, is to probably override all of the functions from your base class returning BinaryTree with a method that returns ColorBinaryTree. Then in the implementation of the child class call the parent's method and perform the cast there before returning. That way you don't have a million casts spread out in your code. It might look like this: