上文代码加上 public TreeNode createTree(String str) { Stack<TreeNode> st=new Stack<TreeNode>(); TreeNode p=null; boolean flag=true; char ch; int i=0; while (i<str.length()) ch=str.charAt(i); switch(ch) { case '(': st.push(p); flag=true; break; case ')': st.pop(); break; case ',': flag=false; break; default: p=new TreeNode(ch); if (root==null) root=p; else { if (flag) { if (!st.empty()) st.peek().leftChild=p; } else { if (!st.empty()) st.peek().rightChild=p; } } break; } i++; } return root; } public static class TreeNode { private TreeNode leftChild; private TreeNode rightChild; private char item; public TreeNode(char item) { this(null, null, item); } public TreeNode(TreeNode leftChild, TreeNode rightChild, char item) { this.leftChild = leftChild; this.rightChild = rightChild; this.item = item; } } }

好的，那么我来补全代码。请注意，下面的代码可能需要一些微调才能完全适应您的程序。

public class Main6 {
    private TreeNode root;
    
    public Main6() {
        root = null;
    }
    
    public TreeNode createTree(String str) {
        Stack<TreeNode> st = new Stack<TreeNode>();
        TreeNode p = null;
        boolean flag = true;
        char ch;
        int i = 0;
        while (i < str.length()) {
            ch = str.charAt(i);
            switch(ch) {
                case '(':
                    st.push(p);
                    flag = true;
                    break;
                case ')':
                    st.pop();
                    break;
                case ',':
                    flag = false;
                    break;
                default:
                    p = new TreeNode(ch);
                    if (root == null) {
                        root = p;
                    } else {
                        if (flag) {
                            if (!st.empty()) {
                                st.peek().leftChild = p;
                            }
                        } else {
                            if (!st.empty()) {
                                st.peek().rightChild = p;
                            }
                        }
                    }
                    break;
            }
            i++;
        }
        return root;
    }
    
    public void inOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        inOrder(root.leftChild);
        System.out.print(root.item + " ");
        inOrder(root.rightChild);
    }
    
    public static class TreeNode {
        private TreeNode leftChild;
        private TreeNode rightChild;
        private char item;
        
        public TreeNode(char item) {
            this(null, null, item);
        }
        
        public TreeNode(TreeNode leftChild, TreeNode rightChild, char item) {
            this.leftChild = leftChild;
            this.rightChild = rightChild;
            this.item = item;
        }
    }
}

需要注意的是，这段代码中的 `TreeNode` 类需要有 `leftChild` 和 `rightChild` 两个属性，表示左子节点和右子节点。另外，程序中的 `root` 变量需要在类中定义。