notification

        NotificationManager notifManager = null;
        final int NOTIFY_ID = 0; // ID of notification
        String id = "12345qwerty"; // default_channel_id
        String channelTitle = "qwerty"; // Default Channel
        Intent intent;
        PendingIntent pendingIntent;
        NotificationCompat.Builder builder;
        notifManager = (NotificationManager)this.getSystemService(Context.NOTIFICATION_SERVICE);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            int importance = NotificationManager.IMPORTANCE_HIGH;
            NotificationChannel mChannel = notifManager.getNotificationChannel(id);
            if (mChannel == null) {
                mChannel = new NotificationChannel(id, channelTitle, importance);
                mChannel.enableVibration(true);
                mChannel.setVibrationPattern(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400});
                notifManager.createNotificationChannel(mChannel);
            }
            builder = new NotificationCompat.Builder(this, id);
            intent = new Intent(this, MainActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
            pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
            builder.setContentTitle(body)                            // required
                    .setSmallIcon(R.drawable.ic_code_black_24dp)   // required
                    .setContentText(this.getString(R.string.app_name)) // required
                    .setDefaults(Notification.DEFAULT_ALL)
                    .setAutoCancel(true)
                    .setContentIntent(pendingIntent)
                    .setTicker(body)
                    .setVibrate(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400});
        }
        else {
            builder = new NotificationCompat.Builder(this, id);
            intent = new Intent(this, MainActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
            pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
            builder.setContentTitle(body)                            // required
                    .setSmallIcon(R.drawable.ic_code_black_24dp)   // required
                    .setContentText(this.getString(R.string.app_name)) // required
                    .setDefaults(Notification.DEFAULT_ALL)
                    .setAutoCancel(true)
                    .setContentIntent(pendingIntent)
                    .setTicker(body)
                    .setVibrate(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400})
                    .setPriority(Notification.PRIORITY_HIGH);
        }
        Notification notification = builder.build();
        notifManager.notify(NOTIFY_ID, notification);