NotificationSample_sendNotificationWithSmallIcon.java

private void sendNotificationWithSmallIcon(String title, String messageBody) 
{
    Bitmap largeIcon = BitmapFactory.decodeResource(getResources(), R.mipmap.user);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
            .setSmallIcon(R.mipmap.ic_launcher)
            .setLargeIcon(largeIcon)
            .setContentTitle(title)
            .setAutoCancel(true)
            .setContentText(messageBody);

    NotificationManager notificationManager =
            (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

    notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
}