java代码实现创建一棵二叉链表表示的二叉树中，实现以广义表表示构造二叉树,并采用先根、中根、后根、层次算法输出二叉树字符

以下是Java代码实现：

import java.util.LinkedList;

public class BinaryTree {

    // 二叉树结点类
    private class Node {
        char val;
        Node left;
        Node right;
        Node(char val) {
            this.val = val;
            this.left = null;
            this.right = null;
        }
    }

    // 根结点
    private Node root;

    // 以广义表表示构造二叉树
    public void createBinaryTree(String str) {
        LinkedList<Node> stack = new LinkedList<>();
        Node node = null;
        boolean flag = false; // 标记是否为左子树
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (c == '(') {
                stack.push(node);
                flag = true; // 下一个结点为左子树
            } else if (c == ')') {
                stack.pop(); // 弹出栈顶结点
            } else if (c == ',') {
                flag = false; // 下一个结点为右子树
            } else {
                node = new Node(c); // 创建新结点
                if (root == null) {
                    root = node; // 第一个结点为根结点
                } else {
                    if (flag) {
                        stack.peek().left = node; // 左子树
                    } else {
                        stack.peek().right = node; // 右子树
                    }
                }
            }
        }
    }

    // 先根遍历
    public void preOrder(Node node) {
        if (node != null) {
            System.out.print(node.val + " ");
            preOrder(node.left);
            preOrder(node.right);
        }
    }

    // 中根遍历
    public void inOrder(Node node) {
        if (node != null) {
            inOrder(node.left);
            System.out.print(node.val + " ");
            inOrder(node.right);
        }
    }

    // 后根遍历
    public void postOrder(Node node) {
        if (node != null) {
            postOrder(node.left);
            postOrder(node.right);
            System.out.print(node.val + " ");
        }
    }

    // 层次遍历
    public void levelOrder(Node root) {
        LinkedList<Node> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            Node node = queue.poll();
            System.out.print(node.val + " ");
            if (node.left != null) {
                queue.offer(node.left);
            }
            if (node.right != null) {
                queue.offer(node.right);
            }
        }
    }

    public static void main(String[] args) {
        BinaryTree tree = new BinaryTree();
        String str = "A(B(D,E(G,)),C(,F))";
        tree.createBinaryTree(str);
        System.out.print("先根遍历：");
        tree.preOrder(tree.root);
        System.out.println();
        System.out.print("中根遍历：");
        tree.inOrder(tree.root);
        System.out.println();
        System.out.print("后根遍历：");
        tree.postOrder(tree.root);
        System.out.println();
        System.out.print("层次遍历：");
        tree.levelOrder(tree.root);
    }
}

输出结果：

先根遍历：A B D E G C F 
中根遍历：D B G E A C F 
后根遍历：D G E B F C A 
层次遍历：A B C D E F G