Question

there is a poker-system in java, that uses Collections.shuffle() on all available cards before the cards are dealt.

So a collection of 52 cards 2-9, J, Q, K, A in 4 types.

After that we Collections.shuffle().

The problem is, that it seems (until now we didn’t have big statistic, it’s possible that we only see a lot of statistic inferences), that the algorithm is VERY unclearly.

So, is Collections.shuffle() okay for a poker algorithm?

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Answers to comments:
With “unclearly” I mean it’s very very mysteriq at some time. Much User complain about “it’s not the same as live / other pokerrooms”.
I played a much with this system and must say, I agree, I see 3 Royal Flashs in under 2000 played hands in this system and live/in other pokerrooms with over 100.000 played hands I see 2 until today.

Answer 1

If this is a serious poker application, where money can change hands, the short answer is NO. For something like this, you should really use a hardware source of true randomness.

The slightly longer answer is: if you can’t get hardware for doing true randomness, Collections.shuffle(List, Random) might be good enough if you supply a SecureRandom. The tricky part with this solution is finding a good seed value.

UPDATE: Based on your clarification, I’d suggest you look into how you’re seeding the PRNG (assuming you’re already using a cryptographically secure implementation; if not, do that first). You should not be using a limited set of seeds. Other things to consider:

• you should probably instantiate a single PRNG for each game
• you should only be shuffling the deck between hands; from your question, it’s not 100% clear that you aren’t also shuffling the deck between the flop, turn, river, etc.