import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class UDP_client {
 public static void main(String[] args) throws IOException {
 //1.创建对象
 //构造数据报套接字并将其绑定到本地主机上任何可用的端口。
 DatagramSocket socket = new DatagramSocket();
 //2.打包
 byte[] arr = "客户端：哈哈。。。。".getBytes();
 //四个参数: 包的数据 包的长度 主机对象 端口号   
 DatagramPacket packet = new DatagramPacket
  (arr, arr.length,InetAddress.getByName("10.0.122.255") , 4000);
 
 //3.发送
 socket.send(packet);
 
 //4.关闭资源
 socket.close();
 }
 
}

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.util.Arrays;


public class UDP_server {
 public static void main(String[] args) throws IOException {
 //1
 DatagramSocket serverSocket = new DatagramSocket(4000);
 //2
 byte[] arr = new byte[1024];
 DatagramPacket packet = new DatagramPacket(arr, arr.length);
 
 //3 当程序运行起来之后,receive方法会一直处于监听状态
 serverSocket.receive(packet);
 //从包中将数据取出
 byte[] arr1 = packet.getData();
 System.out.println(new String(arr1));
 
 //4
 serverSocket.close();
 }
}