Deck Of Cards

Problem Statement

Your assignment is to code in Java a set of classes that represent a deck of poker-style playing cards. (Fifty-two playing cards in four suits: hearts, spades, clubs, diamonds, with face values of Ace, 2-10, Jack, Queen, and King.) Within one of your classes, you must provide two operations:

shuffle()

Shuffle returns no value, but results in the cards in the deck being randomly permuted.

dealOneCard()

This function should return one card from the deck to the caller. Specifically, a call to shuffle() followed by 52 calls to dealOneCard() should result in the caller being provided all 52 cards of the deck in a random order. If the caller then makes a 53rd call dealOneCard(), no card is dealt.

Shuffle Algorithm

This implementation uses the Fisher–Yates shuffle. The Fisher–Yates shuffle is unbiased, unlike many other implementations. It is important for a shuffle algorithm to be unbiased otherwise patterns start to emerge. Jeff Atwood's Coding Horror blog explains what happens when a shuffle algorithm is biased. The same post also has a few good examples of biased shuffle algorithms.

Fisher–Yates is also the algorithm that the Java JDK uses for Collections.shuffle().

How does Fisher–Yates work?

Fisher–Yates shuffles the elements in place by starting at the back and moving forward, swapping the current element with a random element in the front. This removes the need for a second collection in memory. A very good visual explanation can be found here. See the last example.

How was randomness tested?

Testing randomness can be difficult -- it's random. I implemented Shuffler's constructors to make the implementation more testable by allowing the client to pass in a source of randomness represented by the Java Random class. By externalizing Shuffler's randomness I can better control the testing environment.

My code uses an algorithm similar to the algorithm used by Collections.shuffle(). Because the JDK also uses Fisher-Yates, I can use it as a baseline for testing. If I give Collections.shuffle() the same input (the same randomness and the same list of objects to shuffle) as my Shuffler the results should be the same.

Improvements

• PlayingCard FaceValue of an Ace should be able to be represented as high or low.
• Spring should be used for dependency injection.
• Replace Assert class with Spring Assert class