Blackjack Solution Overview

In Preliminary Survey of Classes we’ll present a survey of the new classes gleaned from the general problem statement in Problem Statement as well as the problem details in Blackjack Details. This survey is drawn from a quick overview of the key nouns in these sections. We will not review those nouns already examined for Craps and Roulette.

From the nouns we can start to define some classes. We’ll present this in Preliminary Class Structure.

We’ll confirm our notion with a walk-through of parts of a scenario. We’ll show this in A Walkthrough.

In Blackjack Solution Questions and Answers we’ll provide some additional ideas on the overall solution.

Preliminary Survey of Classes

In reading the background information and the problem statement, we noticed a number of nouns that seemed to be new to the game of Blackjack.

• Card

• Deck

• Point Value

• Hand

• Number Card

• Face Card

• Offer

• Insurance

• Split

• Double

• Hit

• Stand

• Player

• Game

The following table summarizes some of the new classes and responsibilities that we can identify from the problem statement. This is not the complete list of classes we need to build. As we work through the exercises, we’ll discover additional classes and rework some of these classes more than once.

We also have a legacy of classes available from the Roulette and Craps solutions. We would like to build on this infrastructure as much as possible.

Preliminary Class Structure

Card

Responsibilities

Three apparent subclasses: NumberCard, FaceCard and AceCard

A standard playing card with a rank and a suit. Also has a point value from 1 to 11. Aces have point values that depend on the Hand.

Collaborators

Collected in a Deck; collected into Hand instances for each Player; collected into a Hand for the dealer; added to by Game.

Deck

Responsibilities

A complete set of 52 standard Card instances.

Collaborators

Used by the Game to contain Card instances.

Hand

Responsibilities

A collection of Card instances with one or two point values: a hard value (an ace counts as 1) and a soft value (an ace counts as 11). The house will reveal one Card to the player.

Collaborators

A Player may have 1 or more Hand instances; a Hand has 2 or more Card instances. The Game adds Card instances to the Hand. The Game checks the number of cards, the point totals and the ranks of the cards to offer different bets. The Game compares the point totals to resolve bets.

Player

Responsibilities

Places the initial ante Bet instances, updates the stake with amounts won and lost. Accepts or declines offered additional bets, including insurance, and split. Accepts or declines offered resolution, including even money. Chooses among hit, double and stand options.

Collaborators

Uses Table, and one or more Hand instances. Examines the dealer’s Hand. Used by game to respond to betting offers. Used by Game to record wins and losses.

Game

Responsibilities

Runs the game: offers bets to Player, deals the Cards from the Deck to Hand instances, updates the state of the game, collects losing bets, pays winning bets. Splits Hand instances. Responds to player choices of hit, double and stand. This encapsulates the basic sequence of play into a single class.

Collaborators

Uses Deck, Table, Outcome, Player.

A Walkthrough

The unique, new feature of Blackjack is the more sophisticated collaboration between the game and the player. This interaction involves a number of offers for various bets, and bet resolution. Additionally, it includes offers to double, hit or stand. We’ll examine parts of a typical sequence of play to assure ourselves that we have all of the necessary collaborations and responsibilities.

A good way to structure this task is to do a CRC walk-through. For more information on this technique see A Walk-Through of Roulette. We’ll present the overall sequence of play, and leave it to the student to manage the CRC walk-through.

Typical Blackjack Game

1. Place Bets. The Game will ask the Player to place a bet. If the player doesn’t place a bet, the session is over.

2. Create Hands. The Game will deal two cards to the Player’s initial Hand.

   The Game will create an initial hand of two cards for the dealer. One of the cards is the up card, and is visible to the player.

3. Insurance? The Game gets the Dealer’s Hand’s up card. If it is an Ace, then insurance processing is perforemed.

   1. Offer Even Money. The Game examines the Player’s hand for two cards totalling a soft 21, blackjack. If so, the Game offers the Even Money resolution to the Player. If the player accepts, the entire game is resolved at this point. The ante is paid at even money; there is no insurance bet.

   2. Offer Insurance. The Game offers insurance to the Player, who can accept by creating a bet. For players with blackjack, this is a second offer after even money is declined. If the player declines, there are no further insurance considerations.

   3. Examine Hole Card. The Game examines the Dealer’s Hand’s hole card. If is is a 10-point value, the insurance bet is resolved as a winner, the ante is resolved as a loser, and for this player, the game is over. Otherwise the insurance is resolved as a loser, the hole card is not revealed, and play will continue. Note that in a casino with multiple players, it is possible for a player declining insurance to continue to play with the dealer’s hole card revealed. For casinos that offer “early surrender” this is the time to surrender.

4. Split? The Game examines the Player’s Hand to see if the two cards are of equal rank. If so, it offers a split. The player accepts by creating an additional Bet. The original hand is removed; The Game splits the two original Cards then deals two additional Cards to create two new Hands.

   Some casinos prevent further splitting, others allow continued splitting of the resulting hands.

5. Play Out Player Hands. The following are done to play out each of the Player’s Hands.

   1. Bust? Double? Hit? Stand? While the given Hand is under 21 points, the Game must extend three kinds of offers to the Player. If the Player accepts a Hit, the hand gets another card and this process repeats.

      If the Player accepts Double Down, the player must create an additional bet, and the hand gets one more card and play is done. If the Player Stands Pat, the play is done. If the hand is 21 points or over, play is done.

   2. Resolve Bust. The Game must examine each Hand; if it is over 21, the Hand is resolved as a loser.

6. Play Out Dealer Hand. The Game then examines the Dealer Hand and deals Cards on a point value of 16 or less, and stops dealing Cards cards on point value of 17 or more.

   1. Dealer Bust? The Game then examines the Dealer Hand to see if it is over 21. If so, the player’s bets are resolved as winners. Player Hands with two cards totalling 21 ( “blackjack” ) are paid 3:2, all other hands are paid 1:1.

7. Compare Hands. For each hand still valid, the Game compares the Player’s Hand point value against the Dealer’s Hand point value. Higher point value wins. In the case of a tie, it is a push and the bet is returned.

   When the Player wins, a winning hand with two cards totalling 21 (“blackjack”) is paid 3:2, any other winning hand is paid 1:1.

Blackjack Solution Questions and Answers

Will we really need both Deck and the multiple deck Shoe? Wouldn’t it be simpler to combine this functionality into a single class?

There are two separate responsibilities here. The deck owns the basic responsibility to build the 52 cards. The shoe, on the other hand, owns the responsibility to deal cards to hands without dealing all of the available cards. Typically, 52 to 104 cards are held back from play.

We want to be able to simulate games with 1 to 8 decks. A single deck game can simply deal directly from the deck. In a multi-deck game, all of the decks are shuffled together and loaded into a small box (called a “shoe”) for dealing. The difference between one deck and a five-deck shoe is that the shoe can produce 20 kings in a row. While rare, our simulation does need to cover situations like this.

Also, we may want to build a slightly different shoe that simulates the continuous shuffling machine that some casinos use. In this case, each hand is reshuffled back into the shoe, preventing any attempt at card counting. We don’t want to disturb the basic, common deck when introducing this additional feature.

Won’t all those player interactions break our design?

That’s unlikely. All of the player interactions are in addition to the placeBets() interface. Since we’ve separated the core features of all players from the game-specific features, we can add a subclass to player that will be handle the Blackjack interaction. This new player subclass will have a number of additional methods to handle insurance, even money, split and the regular play questions of hit, double and stand.

In parallel, we’ve separated the core features of all games from the unique features for a specific game. We can now add a subclass for Blackjack which adds a number of methods to offer insurance, even money, split and the regular play questions of hit, double and stand to the Blackjack player.

I can’t find an Outcome in Blackjack. Is it the Ante? If so, the odds vary based on the player’s Hand, but that doesn’t seem to be a RandomEvent.

Good point. We’ll examine this in detail in the exercises. Clearly, the bets are placed on the Ante and Insurance as the two core Outcome objects in Blackjack. The Insurance outcome (really a “dealer has blackjack” outcome) is fixed at . The ante payoff depends on a complex condition of the hand: for a soft 21, or blackjack, it pays ; otherwise it pays 1:1. This will lead to a new subclass of the Outcome class that collaborates with the hand to determine the payout to use.

The “even money” is offered before ordinary insurance to a player with blackjack. It, however, pays even money on the ante, and doesn’t create a new bet; in this respect it could be thought of as a change in the outcome on which the ante bet is created. Accepting the even money offer is a little bit like moving the ante to a “even money for dealer blackjack” outcome, which has 1:1 odds instead of odds. Further, this special outcome is resolved before the dealer peeks at their hole card. Perhaps this is a special best resolution procedure, not a proper instance of the Outcome class.

Looking Forward

The first part of the design for Blackjack requires a design for handling cards, and the randomizer subclasses that model the deck and the dealering shoe. We’ll look at all of these closely-related classes in the next chapter.