sermo-de-arboribus / poker

A small library for evaluating poker hands

Poker

A small library for evaluating two poker hands against each other.

Usage

The basic unit of this class is a CardHand object. A CardHand object holds five cards. Every CardHand object maintains the current rank it has, e. g. FLUSH, or TWO_PAIRS, which can be read by calling getRank() on a CardHand object.

Two CardHand objects can be ranked against each other using an object of the Ranker class. The Ranker class method rankHands takes two hands as a parameter and return the winning hand:

Ranker ranker = new Ranker();
CardHand result = ranker.rankHands(hand1, hand2);

Testing

The library comes with unit tests for ensuring the ranking of hands against each other is correctly determining the winner. You can see these tests in action by cloning this repo and then running the tests with Maven:

mvn test

Implementation note

Although Poker cards have no order defined on suits (e. g. a diamond 5 is not more or less "valuable" than a spade 5), this implementation does internally use a sort order not only for card values, but also for card suits. This allows us to use the data structure of a SortedSet internally, which in turn gives us a natural and relatively efficient way of determining the rank of a hand, while the determining of a winner when comparing two hands with each other does not necessarily benefit from this. We assumed here that in a real-life Poker computer game, the determination of a single hand's rank needs to be done more often than the ranking of hands against each other: The single hand's rank needs to be evaluated and displayed on the player's screen, whenever she exchanged some cards. The ranking of different player's hands against each other only needs to be done once per game, at the end of it. That's why we optimized the single hand's rank evaluation by using a sort order for cards that is "stricter" than the sort order of the Poker game's specifications.