mRegistrationBroadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Config.REGISTRATION_COMPLETE)) {
                                    FirebaseMessaging.getInstance().subscribeToTopic(Config.TOPIC_GLOBAL);

                displayFirebaseRegId();

            } else if (intent.getAction().equals(Config.PUSH_NOTIFICATION))
              {
                String message = intent.getStringExtra("message");

                Toast.makeText(getApplicationContext(), "Push notification: " + message, Toast.LENGTH_LONG).show();

                txtMessage.setText(message);
            }
        }
    };

    displayFirebaseRegId();
}

    private void displayFirebaseRegId() {
    SharedPreferences pref = getApplicationContext().getSharedPreferences(Config.SHARED_PREF, 0);
    String regId = pref.getString("regId", null);

    Log.e(TAG, "Firebase reg id: " + regId);

    if (!TextUtils.isEmpty(regId))
        txtRegId.setText("Firebase Reg Id: " + regId);
    else
        txtRegId.setText("Firebase Reg Id is not received yet!");
 }

@Override
protected void onResume() {
    super.onResume();
   LocalBroadcastManager.getInstance(this).registerReceiver(mRegistrationBroadcastReceiver,
            new IntentFilter(Config.REGISTRATION_COMPLETE));
   LocalBroadcastManager.getInstance(this).registerReceiver(mRegistrationBroadcastReceiver,
            new IntentFilter(Config.PUSH_NOTIFICATION));

    NotificationUtils.clearNotifications(getApplicationContext());
}

@Override
protected void onPause() {
    LocalBroadcastManager.getInstance(this).unregisterReceiver(mRegistrationBroadcastReceiver);
    super.onPause();
}

compile 'com.google.firebase:firebase-messaging:11.0.4'