为单独的类文件编写方法(writing a method for a seperate class file)

 我有一个名为UBT.class的.class文件（我无法访问源代码）。 我需要从UBT.class文件中检索数据。 我可以从UBT类（不使用TreeNode类中的方法）访问诸如.getRoot（）和.getLeft（）＆。getRight（）之类的方法。 
 
 我尝试使用像这样的递归来编写一个inOrder遍历方法，但它给出了我下面的错误，虽然我指定它是UBT而不是TreeNode 
 
 错误：不兼容的类型：TreeNode无法转换为UBT 
 
//From main method

     public static void inOrder(UBT root)
      {
        if(root.getRoot() != null)
        {
          inOrder(root.getRoot().getLeft());
          System.out.println(root.getRoot().getData() + " ");
          inOrder(root.getRoot().getRight());
        }
      }

class TreeNode
{
  private int data;
  private TreeNode left, right;

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

  public int getData() {
    return data;
  }

  public void setData(int newData){
    this.data = newData;
  }

  public TreeNode getLeft() {
    return left;
  }

  public TreeNode getRight() {
    return right;
  }

  public void setLeft(TreeNode left) {
    this.left = left;
  }

  public void setRight(TreeNode right) {
    this.right = right;
  }
}

class BST // Typical BST implementation

I have a .class file named UBT.class (which i do not have access to the source code). I need to retrieve data from the UBT.class file. I have access to methods such as .getRoot() & .getLeft() & .getRight() from the UBT class (Not using the methods from the TreeNode class). 
 
I tried writing an inOrder traversal method using recursion like this but its giving me errors like below although i specifiy it to be UBT not TreeNode
 
Error: incompatible types: TreeNode cannot be converted to UBT 
 
//From main method

     public static void inOrder(UBT root)
      {
        if(root.getRoot() != null)
        {
          inOrder(root.getRoot().getLeft());
          System.out.println(root.getRoot().getData() + " ");
          inOrder(root.getRoot().getRight());
        }
      }

class TreeNode
{
  private int data;
  private TreeNode left, right;

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

  public int getData() {
    return data;
  }

  public void setData(int newData){
    this.data = newData;
  }

  public TreeNode getLeft() {
    return left;
  }

  public TreeNode getRight() {
    return right;
  }

  public void setLeft(TreeNode left) {
    this.left = left;
  }

  public void setRight(TreeNode right) {
    this.right = right;
  }
}

class BST // Typical BST implementation

原文：https://stackoverflow.com/questions/35531533