将Java代码从使用Ints转换为字符串

Question

我一直在将我的代码从int更改为字符串。我已经转换了所有内容但只有两行，我知道我应该能够使用compareTo来使它工作，但我不明白如何改变

if(key<insNode.getKey()){

有关如何执行此操作的任何提示？或者是比较改变这个的最好方法吗？

     public class BSTcode {

            public class Node {

                private Node left;
            private Node right;
            private String key;

            public Node(String key){
                this.key = key;
                left = null;
                right = null;
            }

            public void setLeftLeaf(Node left){
                this.left = left;
            }

            public void setRightLeaf(Node right){
                this.right = right;
            }

            public Node getLeftLeaf(){
                return left;
            }
            public Node getRightLeaf(){
                return right;
            }
            public void setKey(String k){
                this.key = k;
            }
            public String getKey(){
                return key;
            }
            public void print(){
                System.out.println("The number is "+ getKey());
            }
        }

        Node root;
        public Node getRoot(){

            return root;
        }

        public BSTcode(){
            root = null;
        }

        public void insert (String key){
             Node n1 = new Node(key);

             if(root == null){
                 root = n1;
             }
             else{
                 Node parIns = root;
                 Node insNode = root;

                 while(insNode!= null){
                     parIns = insNode;

                     if(key<insNode.getKey()){
                         insNode =insNode.getLeftLeaf();

                     }
                     else{
                         insNode = insNode.getRightLeaf();
                     }

                 }
                 if(key<parIns.getKey()){
                     parIns.setLeftLeaf(n1);
                 }
                 else{
                     parIns.setRightLeaf(n1);
                 }
             }

                 }
                 public void printInorder(Node n){

                     if(n!= null){
                         printInorder(n.getLeftLeaf());
                         n.print();
                         printInorder(n.getRightLeaf());
             }

        }
    }