Can't open Java Server Socket on Android

Question

I'm trying to program a simple Android chat program. For testing I want to have the server and the client running on the same device. I'm currently stuck with the very first step of setting up the server part and I simply don't know what I'm doing wrong. (The server will late be run in an own thread)

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    int port = 4444;

    try {
        ServerSocket serverSocket = new ServerSocket(port);
        Log.i("Info", "Server socket initiated on port" + port);

    } catch (IOException e) {
        Log.e("Error", "Could not listen on port " + port);
    }
  }
}

I tried lots of different ports but I still get the IO Error. I also tried to simply use new ServerSocket(0) to allocate a free port using the following code:

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ServerSocket serverSocket = null;

    try {
        serverSocket = new ServerSocket(0);
        Log.i("Info", "Server socket initiated on port" + serverSocket.getLocalPort());

    } catch (IOException e) {
        Log.e("Error", "Could not listen on port " + serverSocket.getLocalPort());
    }
  }
}

But this simply returs a port number of -1 which means the serversocket still isn't bound to anything.

Answer 1

The answer was to add the permission in the manifest. Thx!