public static void main(String[] args) { 
 
  try { 
    Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces(); 
    while (interfaces.hasMoreElements()) { 
      NetworkInterface iface = interfaces.nextElement(); 
      System.out.println("Interface: " + iface.getName()); 
       
      Enumeration<InetAddress> addrList = iface.getInetAddresses(); 
      if (!addrList.hasMoreElements()) 
        System.out.println("No address"); 
       
      while (addrList.hasMoreElements()) { 
        InetAddress address = addrList.nextElement(); 
        System.out.println("Address: " + address.getHostAddress()); 
      } 
    } 
     
  } catch (SocketException e) { 
    e.printStackTrace(); 
  } 
   
} 

public static void main(String[] args) throws IOException { 
 
  String server = args[0]; 
  byte[] data = args[1].getBytes(); 
  int port = 7; 
   
  Socket socket = new Socket(server, port); 
  System.out.println("Connected to server..."); 
   
  InputStream in = socket.getInputStream(); 
  OutputStream out = socket.getOutputStream(); 
   
  out.write(data); 
   
  int totalBytesRcvd = 0; 
  int bytesRcvd; 
  while (totalBytesRcvd < data.length) { 
    if ((bytesRcvd = in.read(data, totalBytesRcvd,  
        data.length - totalBytesRcvd)) == -1) 
      throw new SocketException("Connection closed"); 
    totalBytesRcvd += bytesRcvd; 
  } 
   
  System.out.println("Received: " + new String(data)); 
   
  socket.close(); 
} 

private static final int BUFSIZE = 32; 
 
public static void main(String[] args) throws IOException { 
 
  ServerSocket serverSocket = new ServerSocket(7); 
   
  int recvMsgSize; 
  byte[] receiveBuf = new byte[BUFSIZE]; 
  while (true) { 
    Socket socket = serverSocket.accept(); 
    System.out.println("Handling client " + 
        " from remote " + socket.getRemoteSocketAddress() +  
        " at local " + socket.getLocalSocketAddress()); 
     
    InputStream in = socket.getInputStream(); 
    OutputStream out = socket.getOutputStream(); 
     
    while ((recvMsgSize = in.read(receiveBuf)) != -1) { 
      out.write(receiveBuf, 0, recvMsgSize); 
    } 
    socket.close(); 
  } 
   
} 

public static void main(String[] args) throws IOException { 
 
  InetAddress serverAddress = InetAddress.getByName(args[0]); 
  byte[] bytesToSend = args[1].getBytes(); 
   
  DatagramSocket socket = new DatagramSocket(); 
  socket.setSoTimeout(3000); 
   
  DatagramPacket sendPacket = new DatagramPacket( 
    bytesToSend, bytesToSend.length, serverAddress, 7); 
   
  DatagramPacket receivePacket = new DatagramPacket( 
    new byte[bytesToSend.length], bytesToSend.length); 
   
  // Packets may be lost, so we have to keep trying 
  int tries = 0; 
  boolean receivedResponse = false; 
  do { 
    socket.send(sendPacket); 
    try { 
      socket.receive(receivePacket); 
      if (!receivePacket.getAddress().equals(serverAddress)) 
        throw new IOException("Receive from unknown source"); 
      receivedResponse = true; 
    }  
    catch (IOException e) { 
      tries++; 
      System.out.println("Timeout, try again"); 
    } 
  } while (!receivedResponse && tries < 5); 
   
  if (receivedResponse) 
    System.out.println("Received: " + new String(receivePacket.getData())); 
  else 
    System.out.println("No response"); 
   
  socket.close(); 
} 

private static final int ECHOMAX = 255;  
 
public static void main(String[] args) throws IOException { 
 
  DatagramSocket socket = new DatagramSocket(7); 
  DatagramPacket packet = new DatagramPacket(new byte[ECHOMAX], ECHOMAX); 
   
  while (true) { 
    socket.receive(packet); 
    System.out.println("Handling client at " + packet.getAddress()); 
     
    socket.send(packet); 
    packet.setLength(ECHOMAX); 
  } 
   
}