递归二叉树插入

Question

When I added node into binary tree and trying to show information about it, info isn't showing. I think that i have some problems with references in recursive insert algorithm, but can't fix it.

package test;

class BinaryTree<T> {
    private static class Node<T> {
        int key;
        T data;
        Node<T> leftChild;
        Node<T> rightChild;

        public Node(int key,T data) {
            this.key = key;
            this.data = data;
        }
    }

    public Node<T> rootNode;

    public BinaryTree() {
        rootNode = null;
    }

    public Node<T> getRootNode() {
        return rootNode;
    }

    // insert node into binary tree
    public void insertNode(int key,T data, Node<T> rootNode) {
        // to create new node

        // if tree doesn't have root elements
        if(rootNode == null) {
            rootNode = new Node<T>(key,data);
            rootNode.leftChild = null;
            rootNode.rightChild = null;
        }
        else {
            Node<T> focusNode = rootNode;

            if(key >= focusNode.key) {
                insertNode(key,data,focusNode.rightChild);
            }
            else {
                insertNode(key,data,focusNode.leftChild);
            }
        }
    }

    // inorder traverse tree
    public void inOrderTraverseTree(Node<T> focusNode) {
        if(focusNode != null) {
            inOrderTraverseTree(focusNode.leftChild);
            System.out.println(focusNode.data);
            inOrderTraverseTree(focusNode.rightChild);
        }
    }
}

public class MyApp {
    public static void main(String[] args) {
        BinaryTree<String> bintree = new BinaryTree<String>();
        bintree.insertNode(3, "Boss", bintree.rootNode);
        bintree.inOrderTraverseTree(bintree.rootNode);
    }
}

If I'm adding node with this algorithm and trying to show info, it works. How can i fix problem with recursive algorithm?

public void addNode(int key, T name) {
        Node<T> newNode = new Node<T>(key,name);
        if(rootNode == null) {
            rootNode = newNode;
        }
        else {
            Node<T> focusNode = rootNode;
            Node<T> parent;
            while(true) {
                parent = focusNode;
                if(key < focusNode.key) {
                    focusNode = focusNode.leftChild;
                    if(focusNode == null) {
                        parent.leftChild = newNode;
                        return;
                    }
                }
                else {
                    focusNode = focusNode.rightChild;
                    if(focusNode == null) {
                        parent.rightChild = newNode;
                        return;
                    }
                }
            }
        }
    }

Thanks for any help.

Answer 1

Quick glance on your code -- I spotted on this part where you're checking for null, rootNode variable is local to the function . Hence the new Node you created gets thrown away immediately after the function quits, it won't change your member field

    // if tree doesn't have root elements
    if(rootNode == null) {
        rootNode = new Node<T>(key,data);
        rootNode.leftChild = null;
        rootNode.rightChild = null;
    }

You need to use this.rootNode = new Node<T>(key,data); instead, or use a different local variable name to avoid confusion