要实现Android中的默认折叠通知操作，可以按照以下步骤进行：

1. 创建一个通知渠道（Notification Channel）：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    CharSequence name = "Default Channel";
    String description = "Default notification channel";
    int importance = NotificationManager.IMPORTANCE_DEFAULT;
    NotificationChannel channel = new NotificationChannel("default_channel", name, importance);
    channel.setDescription(description);
    NotificationManager notificationManager = getSystemService(NotificationManager.class);
    notificationManager.createNotificationChannel(channel);
}

2. 创建一个通知构建器（Notification Builder）：

NotificationCompat.Builder builder = new NotificationCompat.Builder(this, "default_channel")
        .setSmallIcon(R.drawable.notification_icon)
        .setContentTitle("Notification Title")
        .setContentText("Notification Content")
        .setPriority(NotificationCompat.PRIORITY_DEFAULT)
        .setAutoCancel(true);

3. 添加折叠操作：

Intent intent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

builder.setContentIntent(pendingIntent);

4. 发送通知：

NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(this);
notificationManagerCompat.notify(notificationId, builder.build());

通过以上步骤，你可以创建一个带有默认折叠通知操作的Android通知。