Why Android heaps over a Thread task?

I am trying to check if my server is on/off from an Android application. From my MainActivity I use this code snippet:

try {    new CheckServer().start();} catch (MalformedURLException e) {     throw new RuntimeException(e);}

This is the class:

public class CheckServer extends Thread {    URL url = new URL("server-address");    public CheckServer() throws MalformedURLException {    }    @Override    public void run() {        try        {            HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();            int code = urlConnection.getResponseCode();            Log.d("test", "test connection > " + code);        } catch (IOException e) {            throw new RuntimeException(e);        }    }}

When I run the app, nothing happens(I don't get the message Log). So after a debugging I discovered that in runtime this part was skipped:

public void run() {        try        {            HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();            int code = urlConnection.getResponseCode();            Log.d("test", "test connection > " + code);        } catch (IOException e) {            throw new RuntimeException(e);        }    }

Can anyone show/tell me why or what I am doing wrong? it will be highly appreciate