按照下面先根序列构造二叉树：AB^D^^C^^ 的Java代码

以下是按照先根序列构造二叉树AB^D^^C^^的Java代码：

public class BiTreeNode {
    private String data;
    private BiTreeNode lchild;
    private BiTreeNode rchild;

    public BiTreeNode(String data) {
        this.data = data;
        this.lchild = null;
        this.rchild = null;
    }

    public void setLchild(BiTreeNode lchild) {
        this.lchild = lchild;
    }

    public void setRchild(BiTreeNode rchild) {
        this.rchild = rchild;
    }

    public BiTreeNode getLchild() {
        return lchild;
    }

    public BiTreeNode getRchild() {
        return rchild;
    }

    public String getData() {
        return data;
    }
}

public class BiTree {
    private BiTreeNode root;

    public BiTree(String preOrder) {
        Stack<BiTreeNode> stack = new Stack<>();
        int i = 0;
        char[] chars = preOrder.toCharArray();
        while (i < chars.length) {
            if (chars[i] == '^') {
                if (!stack.isEmpty()) {
                    stack.pop();
                }
            } else {
                BiTreeNode node = new BiTreeNode(chars[i] + "");
                if (root == null) {
                    root = node;
                }
                if (!stack.isEmpty()) {
                    BiTreeNode parent = stack.peek();
                    if (parent.getLchild() == null) {
                        parent.setLchild(node);
                    } else {
                        parent.setRchild(node);
                    }
                }
                stack.push(node);
            }
            i++;
        }
    }

    public BiTreeNode getRoot() {
        return root;
    }
}