java编的小程序 编写出一个聊天室，此聊天室应具备如下功能：

(1) 允许用户注册；

(2) 允许注册用户登陆聊天室；

(3) 登录用户之间进行聊天和文件传输；

(4) 用户可以更改背景和音乐；

-compiled java applet to write a chat room, this chat room should have the following functions: (1) allows the user to register　(2) allows registered users to log chat room　(3) logged-on user chat and file transfers between　( 4) The user can change the background and music