DatagramSocket

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
//from  j  a  va2s.c o  m
public class Main {
  public static void main(String[] argv) throws Exception {
    InetAddress dst = InetAddress.getLocalHost();
    int port = 8080;
    byte[] outbuf = new byte[1024];
    int len = 1024;

    DatagramPacket request = new DatagramPacket(outbuf, len, dst, port);
    DatagramSocket socket = new DatagramSocket();
    socket.send(request);
  }
}

import java.net.DatagramPacket;
import java.net.DatagramSocket;
/*from  j  a  v a 2s .co  m*/
public class Main {
  public static void main(String[] argv) throws Exception {
    byte[] inbuf = new byte[256]; // default size
    DatagramSocket socket = new DatagramSocket();

    DatagramPacket packet = new DatagramPacket(inbuf, inbuf.length);
    socket.receive(packet);

    int numBytesReceived = packet.getLength();
    System.out.println(numBytesReceived);
  }
}

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
/*from  j  av a  2s  .com*/
public class Main {
  public static void main(String[] args) throws Exception {
    byte[] ary = new byte[128];
    DatagramPacket pack = new DatagramPacket(ary, 128);

    // read
    DatagramSocket sock = new DatagramSocket(1111);
    sock.receive(pack);
    String word = new String(pack.getData());
    System.out.println("From: " + pack.getAddress() + " Port: " + pack.getPort());
    System.out.println(word);
    sock.close();
    // write
    sock = new DatagramSocket();
    pack.setAddress(InetAddress.getByName(args[1]));
    pack.setData(args[2].getBytes());
    pack.setPort(1111);
    sock.send(pack);
    sock.close();

  }
}

import java.net.DatagramSocket;
import java.net.SocketException;
/* j  ava2  s.  c  o  m*/
public class MainClass {

  public static void main(String[] args) {

    for (int port = 1024; port <= 65535; port++) {
      try {
        // the next line will fail and drop into the catch block if
        // there is already a server running on port i
        DatagramSocket server = new DatagramSocket(port);
        server.close();
      } catch (SocketException ex) {
        System.out.println("There is a server on port " + port + ".");
      }
    }
  }
}