如何在Java中创建使用二叉搜索树获取前一个节点的方法？

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    public TreeNode(int val) {
        this.val = val;
        this.left = null;
        this.right = null;
    }
}

class BinarySearchTree {
    private TreeNode root;

    public BinarySearchTree() {
        this.root = null;
    }

    // 插入节点
    public void insert(int val) {
        root = insertNode(root, val);
    }

    private TreeNode insertNode(TreeNode root, int val) {
        if (root == null) {
            return new TreeNode(val);
        }

        if (val < root.val) {
            root.left = insertNode(root.left, val);
        } else if (val > root.val) {
            root.right = insertNode(root.right, val);
        }

        return root;
    }

    // 获取前一个节点
    public TreeNode getPredecessor(TreeNode node) {
        if (node == null) {
            return null;
        }

        // 如果节点有左子节点，则前一个节点为左子树中的最右节点
        if (node.left != null) {
            TreeNode predecessor = node.left;
            while (predecessor.right != null) {
                predecessor = predecessor.right;
            }
            return predecessor;
        }

        // 如果节点没有左子节点，则前一个节点为其父节点或祖先节点中第一个比它大的节点
        TreeNode predecessor = null;
        TreeNode current = root;
        while (current != null) {
            if (node.val > current.val) {
                predecessor = current;
                current = current.right;
            } else if (node.val < current.val) {
                current = current.left;
            } else {
                break;
            }
        }
        return predecessor;
    }
}

public class Main {
    public static void main(String[] args) {
        BinarySearchTree bst = new BinarySearchTree();
        bst.insert(5);
        bst.insert(3);
        bst.insert(7);
        bst.insert(2);
        bst.insert(4);
        bst.insert(6);
        bst.insert(8);

        TreeNode node = bst.getPredecessor(bst.root.right.right);
        if (node != null) {
            System.out.println("前一个节点的值为：" + node.val);
        } else {
            System.out.println("该节点没有前一个节点");
        }
    }
}