public class UDPtest1 {
    public UDPtest1() throws Exception {
        DatagramSocket serversocket = new DatagramSocket(3000);
        byte[] b = new byte[100];
        DatagramPacket packet = new DatagramPacket(b, 100);
        serversocket.receive(packet);
        System.out.println(new String(b, 0, packet.getLength()));
        serversocket.close();
    }

    public static void main(String[] args) throws Exception {
        new UDPtest1();
    }

}

public class UDPtest2 {
    public UDPtest2() throws Exception {
        DatagramSocket clientsocket = new DatagramSocket();
        String str = "hello world";
        DatagramPacket packet = new DatagramPacket(str.getBytes(),
                str.length(), InetAddress.getByName("localhost"), 3000);
        clientsocket.send(packet);
        clientsocket.close();
    }

    public static void main(String[] args) throws Exception {
        new UDPtest2();
    }
}