Trees and BST in Java

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

void inorder(TreeNode root) {
    if (root == null) return;
    inorder(root.left);
    System.out.print(root.val + " ");
    inorder(root.right);
}