如何使用自己类型的成员扩展类？

问题描述：

假设我们需要使用一个名为BaseNode的类实现不同类型的树，从中派生出其他类型的节点，它假设有一个名为 parent 的实例变量它自己的类型，通常看起来像：

Suppose we need to implement different types of tree with a class called "BaseNode" from which other type of Nodes are derived and it suppose to have an instance variable called parent of its own type, generally it looks like:

class BaseNode{
   //...some fields
   BaseNode parent;
   //...other methods
}

现在如果我要去为更多成员派生AVL树节点：

Now if I am going to derive Node for AVL tree with more members:

class AVLNode extends BaseNode{
    //...other useful stuff

}

原来的父母（& left & right ）节点成员仍将是 BaseNode 这阻止我实现AVL树。
任何能告诉我如何解决这个继承问题的人？
谢谢！

the original parent (&left&right)node members will still be type BaseNode which prevents me to implement the AVL tree. Any one who could tell me how we could solve this inheritance problem? Thanks!

答

解决方案1  - 任何时候访问 parent ，将其强制转换为（AVLNode）parent 。您可以在 AVLNode 中编写一个访问者，以使其更方便。

Solution 1 - Any time you access parent, cast it to (AVLNode) parent. You could write an accessor in AVLNode to make it more convenient.

class AVLNode extends BaseNode {
    public AVLNode getParent() {
        return (AVLNode) parent;
    }
}

解决方案2 - 制作 BaseNode 将子类作为参数的泛型类。现在 parent 可以是所需的确切类型。

Solution 2 - Make BaseNode a generic class that takes the subclass as a parameter. Now parent can be the exact type needed.

class BaseNode<T extends BaseNode<T>> {
    T parent;
}

class AVLNode extends BaseNode<AVLNode> {
}

如何使用自己类型的成员扩展类？

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