package datagrams;import java.io.*;import java.net.*;public class DatagramsServerString {  public static void main(String[] args) throws IOException {    //應用5556端口創建DatagramSocket類    DatagramSocket datagramSocket = new DatagramSocket(5556);    try {      byte[] buf = new byte[20];      //使用byte數組創建數據包      DatagramPacket packet = new DatagramPacket(buf, buf.length);      System.out.println("等待接收數據.");      //使用DatagramSocket接口接收客戶端的數據包,進入等待狀態      datagramSocket.receive(packet);      String string = "1235";      //將字符串轉為Bytes()數組      buf = string.getBytes();      //根據接收的數據包獲取網絡地址與端口      InetAddress address = packet.getAddress();      int port = packet.getPort();      //重新創建帶有網絡地址與端口的數據包      packet = new DatagramPacket(buf, buf.length, address, port);      //根據數據包的地址與端口發送數據包      datagramSocket.send(packet);      System.out.println("完成數據發送.");    }    catch (IOException e) {      e.printStackTrace();    }  }}