说明：  编写本程序时，所使用的是传输层的UDP协议，不分服务器和客户端，采用对等实体的形似实现信息的传输。运用java.net.DatagramPacket类和java.net.DatagrameSocket类实现套接和数据的传输。并且采用组播形式进行数据信息的传递。使用三个简单协议数据单元（PDU），即JOIN PDU,LEAVE PDU,MESSAGE PDU。分别表示首次连接时组播的数据报、用户离开时组播的数据报，用户输入完消息时组播的数据报。
(preparation of this procedure, which is used in the transport layer UDP, regardless of the server and client, used such entities to realize the huge information transmission. Java.net.DatagramPacket use category and java.net.Data grameSocket Class of molars and data transmission. And using multicast form of the transfer of data information. Use three simple protocol data unit (PDU), the PDU JOIN, LEAVE PDU. MESSAGE PDU. , Said the first link multicast data reported that users leave multicast data reported, End user input information on the multicast data reported.)