java 实现读取英语文章，建立二叉树，程序自动统计每个个字母的使用频率（中序遍历输出每个字符），最后输出所有字母的以二进制表示的哈夫曼编码。-java read articles in English, the establishment of a binary tree, the program automatically statistical frequency of use of each letter (the preorder output for each character),