Java tutorial
import java.net.DatagramSocket; import java.net.SocketException; 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 + "."); } } } }