private interface ConnectionState {
   bool checkState ();
}

private class OkConnectionState : ConnectionState {
   bool checkState () {
      return true;
   }
}

private class FailedConnectionState : ConnectionState {
   bool checkState () {
      return false;
   }
}

void main () {
   ConnectionState c = new OkConnectionState ();
   ConnectionState d = new FailedConnectionState ();
   
   c.checkState ();
}