import java.io.IOException;
import java.net.ServerSocket;
public class MainClass {
public static void main(String[] args) {
for (int port = 1; port <= 65535; port++) {
try {
// the next line will fail and drop into the catch block if
// there is already a server running on the port
ServerSocket server = new ServerSocket(port);
} catch (IOException ex) {
System.out.println("There is a server on port " + port + ".");
}
}
}
}