实现功能：· 用户上线·包括新用户上线和已使用过该系统的用户上线·每位在线的用户将会收到该用户上线的通知·该用户会收到所有已在线的用户的信息·朋友下线 　·服务器端删除该用户信息·每位在线的用户将会收到该用户下线的通知，同时删除改用户的信息·聊天终止，文件传输终止·　修改用户名字·用户可以在对应的文本框内直接修改名称·用户可以在保存的Myinfo.txt中直接修改名称·　聊天功能：·公聊：所有在线的用户都可以看到你的发言·私聊：能和所有以在线的用户进行私聊，其他用户看不到私聊对象之间的聊天　　·文件传输　　·能给所有的已在线用户发送文件（先打开私聊窗口）　　·只能给一位用户发送文件，但是却可以接收多个用户发送的文件·查看历史记录　　·可以查看私聊的聊天记录　　·可以查看公聊的聊天记录　　·可以查看服务器端的所有记录-achieve functional : on-line users, including new users on line and have used the system users on the line every online users will be received by the users of on-line users will be notified of the receipt of all users of online information Linear friends server to delete the user information each of the Line users will receive the notification from the assembly line users, delete users change the information termination chat, file transfer, termination of modifying user names users can text box corresponding directly alter the names of users can keep Myinfo.txt directly change the name chat : public talk : all online users can see you speak of Private Chat : energy and all online users Private Chat, other users see objects Private Chat chat between the file transfer can all have online use