public class Test {
    public static void main(String[] args) throws UnknownHostException {
        Mongo m = new Mongo();
        DBCollection collection = m.getDB("test").getCollection("tmp");
        collection.drop();
        collection.ensureIndex("length");
        for (int i = 0; i < 10; i++) {
            DBObject object = new BasicDBObject("_id", i);
            object.put("length", (int) (Math.random() * 100));
            collection.insert(object);
        }
        DBCursor cursor = collection.find().addSpecial("$max", new BasicDBObject("length", 10));
        System.out.println("cursor.count - " + cursor.count());
        System.out.println("cursor.toArray.size - " + cursor.toArray().size());
    }
}

cursor.count - 10
cursor.toArray.size - 0