可以使用 NotificationChannel 类将通知分类，并设置通知通道的重要性等级为“低”，即可将其归类为静音通知。

示例代码如下：

// 创建一个通知渠道，设置名称和重要性等级
NotificationChannel channel = new NotificationChannel("channel_id", "channel_name", NotificationManager.IMPORTANCE_LOW);

// 将通知归类为静音通知
channel.setCategory(NotificationCompat.CATEGORY_MESSAGE);

// 注册通知渠道
NotificationManager notificationManager = getSystemService(NotificationManager.class);
notificationManager.createNotificationChannel(channel);

// 创建通知并发送
Notification notification = new NotificationCompat.Builder(context, "channel_id")
    .setContentTitle("Title of notification")
    .setContentText("Content of notification")
    .setSmallIcon(R.drawable.notification_icon)
    .build();

notificationManager.notify(notificationId, notification);