马克-to-win：在UDP编程当中，技术上没有一个服务器和客户端的概念，即没有类似于TCP中的ServerSocket类，只有主动和被动之说，客户端和服务器都用DatagramSocket(MyPORT)来绑定到一个端口，发送和接收dataPacket，它们是对等的双方。不过通常来讲，先发送数据的被认为是客户端。in UDP, there is no concept of server or client, onlyactive and passive, client and server both use newDatagramSocket(MyPORT) to bind to a port to use the port to send andreceive the dataPacket, the counterpart which initially send thedataPacket is deemed as the client. unlike the TCP protocol, there,there is really ServerSocket.
UDP通信主要有两个类，DatagramPacket是数据容器，
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