I added a TcpManager class that you can use to enable the user to
connect to a friend, and to send and get information of that friend's
location information in virtual world.

Please use this class to implement the function that the user can see
his friend in the virtual world.

Note:

1. The TcpManager class only returns the most recent Java Object it
received.所以请把玩家某一时刻的所有信息都pack到一个类型里面，这样子每个时刻发送的信息都只需要send一个object（要不然接收端只能收到最后一个object就会丢信息）

2. The TcpManager class is to be implemented by myself, so please don't
be bothered by the deficiency of its actual code.