Java UDP protocol based message sending

package lesson03;

import ;
import ;
import ;

/**
 * :: Transmitter
 */
public class UdpClientDemo1 {

  public static void main(String[] args) throws Exception {

    //Create a Socket
    DatagramSocket socket = new DatagramSocket();

    /**
     * 2. Build a package
     */

    //Messages to be sent
    String msg = "Hello, server!";

    //Send address
    InetAddress localhost = ("localhost"); //Mainframe
    //Send port
    int port = 9090;

    /**
     * Five parameters:
     * @param buf (): the packet to be sent
     * @param offset 0: offset of the data
     * @param length ().length: length of the data
     * @param address localhost: destination address
     * @param port port: destination port
     */
    DatagramPacket packet = new DatagramPacket((), 0, ().length, localhost, port);

    //3. Sending packages
    (packet);

    //4. Closing the stream
    ();
  }

}

package lesson03;

import ;
import ;

/**
 * Receiver
 */
public class UdpServerDemo1 {

  public static void main(String[] args) throws Exception {

    // Open ports
    DatagramSocket socket = new DatagramSocket(9090);

    //Receive packets
    byte[] buffer = new byte[1024];
    DatagramPacket packet = new DatagramPacket(buffer, 0, );

    //Receive
    (packet); //blocking reception

    // Output packet address
    (().getHostAddress());
    /**
     * Output packet data
     * packet: Data type
     * Converted to String type by constructor: new String();
     */
    (new String((), 0, ()));

    // Close the connection
    ();

  }

}