实验目的：掌握二叉树的构建及遍历操作。 实验内容：按先序遍历的顺序构建的二叉树实现先序、中序和后序遍历，并输出对应的遍历序列，节点要用字母表示。 实验要求： 1、构建一个二叉链表存储结构的二叉树。 2、基于上述构建的二叉树进行先序、中序和后序遍历操作。用Java实现

以下是Java代码实现：

public class TreeNode {
    char val;
    TreeNode left;
    TreeNode right;
    TreeNode(char x) { val = x; }
}

public class BinaryTree {
    public TreeNode buildTree(char[] preorder, char[] inorder) {
        if (preorder == null || inorder == null || preorder.length == 0 || inorder.length == 0)
            return null;
        return build(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
    }

    private TreeNode build(char[] preorder, int preStart, int preEnd, char[] inorder, int inStart, int inEnd) {
        if (preStart > preEnd || inStart > inEnd)
            return null;
        char rootVal = preorder[preStart];
        TreeNode root = new TreeNode(rootVal);
        int index = findIndex(inorder, rootVal, inStart, inEnd);
        int leftSize = index - inStart;
        root.left = build(preorder, preStart + 1, preStart + leftSize, inorder, inStart, index - 1);
        root.right = build(preorder, preStart + leftSize + 1, preEnd, inorder, index + 1, inEnd);
        return root;
    }

    private int findIndex(char[] inorder, char val, int start, int end) {
        for (int i = start; i <= end; i++) {
            if (inorder[i] == val)
                return i;
        }
        return -1;
    }

    public void preorder(TreeNode root){
        if(root == null) return;
        System.out.print(root.val + " ");
        preorder(root.left);
        preorder(root.right);
    }

    public void inorder(TreeNode root){
        if(root == null) return;
        inorder(root.left);
        System.out.print(root.val + " ");
        inorder(root.right);
    }

    public void postorder(TreeNode root){
        if(root == null) return;
        postorder(root.left);
        postorder(root.right);
        System.out.print(root.val + " ");
    }

    public static void main(String[] args) {
        BinaryTree tree = new BinaryTree();
        char[] preorder = {'A', 'B', 'D', 'E', 'C', 'F'};
        char[] inorder = {'D', 'B', 'E', 'A', 'F', 'C'};
        TreeNode root = tree.buildTree(preorder, inorder);
        System.out.print("先序遍历结果：");
        tree.preorder(root);
        System.out.print("\n中序遍历结果：");
        tree.inorder(root);
        System.out.print("\n后序遍历结果：");
        tree.postorder(root);
    }
}

输出结果：

先序遍历结果：A B D E C F 
中序遍历结果：D B E A F C 
后序遍历结果：D E B F C A