public class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {
public static final String TAG = "NOTICIAS";

@Override
public void onTokenRefresh() {
    super.onTokenRefresh();

    String token = FirebaseInstanceId.getInstance().getToken();

    Log.d(TAG, "Token: " + token);

    enviarTokenAlServidor(token);
}

private void enviarTokenAlServidor(String token) {
    // Enviar token al servidor
}
}

public class MyFirebaseMessagingService extends FirebaseMessagingService {

public static final String TAG = "NOTICIAS";

@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
    super.onMessageReceived(remoteMessage);

    String from = remoteMessage.getFrom();
    Log.d(TAG, "Mensaje recibido de: " + from);

    if (remoteMessage.getNotification() != null) {
        Log.d(TAG, "Notificación: " + remoteMessage.getNotification().getBody());
        mostrarNotificacion(remoteMessage.getNotification().getTitle(), remoteMessage.getNotification().getBody());
    }

    if (remoteMessage.getData().size() > 0) {
        Log.d(TAG, "Data: " + remoteMessage.getData());
    }
}

private void mostrarNotificacion(String title, String body) {

    //Intent intent = new Intent(this, PushActivity.class);
    Intent intent = new Intent(this, MainActivity.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_ONE_SHOT);

    Uri soundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
            .setSmallIcon(R.drawable.icon)
            .setContentTitle(title)
            .setContentText(body)
            .setAutoCancel(true)
            .setSound(soundUri)
            .setContentIntent(pendingIntent);

    NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    notificationManager.notify(0, notificationBuilder.build());

}
}

public class PushActivity extends AppCompatActivity {

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

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#e70d0d"
tools:context=".firebase.PushActivity">

</FrameLayout>