C#

using System;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace ConsoleApplication25
{
	class Class1
	{
		[STAThread]
		static void Main(string[] args)
		{
			// Start server
			Thread serverThread = new Thread(new ThreadStart(Server));
			serverThread.Start();

			// Wait 1 second
			Thread.Sleep(1000);

			// Start client
			Thread clientThread = new Thread(new ThreadStart(Client));
			clientThread.Start();
		}

		static void Server()
		{
			byte[] buffer = new byte[1000];

			TcpListener tcpListener = new TcpListener(30000);
			tcpListener.Start();

			TcpClient tcpClient = tcpListener.AcceptTcpClient();
			
			NetworkStream networkStream = tcpClient.GetStream();
			networkStream.Read(buffer, 0, buffer.Length);
			
			string stringReceived = Encoding.ASCII.GetString(buffer).Replace("\0", "");

			Console.WriteLine("Server received : " + stringReceived);
		}

		static void Client()
		{
			string stringToSend = "Hello World";
			byte[] buffer = Encoding.ASCII.GetBytes(stringToSend);
			
			TcpClient tcpClient = new TcpClient();
			tcpClient.Connect("localhost", 30000);
			
			NetworkStream networkStream = tcpClient.GetStream();
		
			Console.WriteLine("Client send : " + stringToSend);

			networkStream.Write(buffer, 0, buffer.Length);
		}
	}
}