Declare a Binary Tree which takes a Generic type of Node which contains a Generic type of key value?

问题

If I have a node class(es) that can accept a generic type for it's key value:

class Node<K extends Comparable<K>> implements Comparable<Node<K> {
    ...
}

class KeyValueNode<K extends Comparable<K>, V> extends Node<K> {
    ...
}

Is it possible to declare a generic binary tree class that accepts a generic type of node, which can contain a generic type of key value? I thought it would look something like this....

class BinaryTree<N<K>> {
    N<K> root;
    BinaryTree<N<K>> left, right;
    ...
}

Apologies for any glaring misunderstandings, I'm still trying to get the hang of generics and the syntax in Java, would greatly appreciate any help or insights.

Thanks!

回答1:

A binary tree structure will essentially just hold a reference to the root node. So it should have the same type parameters as its nodes:

class BinaryTree<K extends Comparable<K>> {

    Node<K> root;
}

Or for the key-value design:

class KeyValueBinaryTree<K extends Comparable<K>, V> {

    KeyValueNode<K, V> root;
}

Note that it's debatable whether an enclosing tree class is necessary, since it's the nodes that are pointing to each other.

回答2:

You can say:

class BinaryTree<N extends Node<N>> {
  Node<N> root; 
  // or even better: N root;
  BinaryTree<N> left, right;
}

Having BinaryTree<Node<K>> is not parameterizing the class as is the purpose of defining a generic type.

回答3:

This is how I would write a generic binary tree class

public class BinaryTree<N extends Node<K>, K extends Comparable> {
    N root;
    BinaryTree<N, K> left, right;
}

(Although I assume you would not really story the BinaryTree in a binary tree and that was just for your example to show how it could be declared)

来源：https://stackoverflow.com/questions/10265836/declare-a-binary-tree-which-takes-a-generic-type-of-node-which-contains-a-generi

标签

java

generics

binary-tree

nodes