在方法中找不到符号

Question

我正在尝试构建一个二进制搜索树来按字母顺序排列字符串。

我似乎在编译代码时遇到了问题。

BinarySearchTree.java:14: error: cannot find symbol
    int compareResult = theTreeKey.compareTo(theRoot.NODEkey);
                                  ^
symbol:   method getKey()
location: variable theTreeKey of type Object

我不明白为什么无法找到此符号，因为我将其作为方法中的参数传递。我想不出解决办法，因为我不清楚这个问题。

//Start of BST Class
public class BST {

    TreeCell<String> root;

    public BST() {
        root = null;
    }

    public void insert(String string) {
        root = insert(string, root);
    }

    private static TreeCell<String> insert(String string, TreeCell<String> node) {
        if (node == null)
            return new TreeCell<String>(string);
        int compare = string.compareTo(node.datum);
        if (compare < 0)
            node.left = insert(string, node.left);
        else if (compare > 0)
            node.right = insert(string, node.right);
        return node;
    }
}//End of BST Class


//Start of BinaryTree Class
import java.lang.String;
class BinaryTree
{
    Node TREEroot;

    public void insert(Object treeKey){
        TREEroot=insertNewNode(TREEroot,treeKey);
    }

    public Node insertNewNode(Node theRoot,Object theTreeKey){
        if(theRoot==null)
            return new Node(theTreeKey);

        int compareResult = theTreeKey.compareTo(theRoot.NODEkey);

        if(compareResult < 0)
            theRoot.NodeLeftChild=insertNewNode(theRoot.NodeLeftChild,theTreeKey);
        else if(compareResult > 0)
            theRoot.NodeRightChild=insertNewNode(theRoot.NodeRightChild,theTreeKey);
        else if(compareResult == 0)
            theRoot.count=theRoot.count++;
        return theRoot;
    }
}//End of BinaryTree class

//Start of Node class
import java.io.*;
import java.util.*;

class Node{
        Object NODEkey;
        int count;
        Node NodeLeftChild;
        Node NodeRightChild;

        Node(Object key){
                NODEkey=key;
                count=1;
        }

    public Node getNodeLeftChild(){
        return this.NodeLeftChild;
    }

    public Node getNodeRightChild(){
        return this.NodeRightChild;
    }

    public Object getKey(){
        return this.NODEkey;
    }
}//end of Node class

非常感谢任何见解。