Computer Science 313 – Advanced Programming Topics

Rules of Blackjack  Give each 2 cards at the very start  When dealt cards match, make two hands (split)  Request extra cards during turn (take a hit)  Double bet & take one more card (double down)  Try to get close to 21, without going bust  Number cards (2, 3, 4, 5, …, 10) worth value  10 points for each face card (Jack, Queen, King)  Each player can use Ace as 1 or 11  Players win if they beat dealers hand

Dealer Follows Rules  Dealer automatically wins when starting at 21  Equal scores considered tie, otherwise  Very simple set of rules followed by dealer  Must take hit when hand is under 17  Stands in when hand is high enough (18+)  On “soft-17” casino rules vary  Players should be able to win regularly  Casinos not built on losing  Many “winning” systems exist, however

How To Not Lose Quickly  Track cards remaining in deck  Counting cards legal, but hard…  …counting relative values far easier  Remember how “rich” deck is  For each 10 or higher, subtract 1 point  Add 1 for 7s or lower seen so far  As deck score over many hands  Change strategies to reflect situation

Developing this Program  Simple, straightforward program to write  Make decisions using deck’s current value  Deck’s score stored in a field  Update value each time a card is seen  To beat the house, develop complex set of rules  Write needHit(), doubleDown() and others  Each method has HUGE if-else or switch  Hard to make minor changes to your strategy  Thinking about reusing code? Do not bother.

Was That a Hint?  I left a big clue to solution in last slide  Hopefully, you started thinking design pattern  We already discussed this design pattern  Should be obvious choice to encourage reuse  Algorithm family changed dynamically needed

Developing this Program

I’m Master of the Lost Art

Close but not Quite  Strategy pattern holds obvious allure  Several reasons NOT to use this pattern, however  Reasons why strategy pattern inappropriate  Strategy changes internal to context instance  Means of tracking current state is lacking  Unable to find current strategy being used  For this to work, need to update strategies

State Pattern Intent  Instances alter strategy when state changes  Includes Strategy pattern to define actions  Strategies responsible for changing themselves  Actions & state transitions delegated by instance  Perfect for use with finite state machines  Common tool from theory & software engineering  Can be found in many, many systems  Parsers  Systems performing real-time computing  User interface subsystems

For Next Class  Lab due 1 week from today  Please, please, please do not wait until last minute…  Design is hard, but code is very simple  Give yourself time to think and ask questions  Read up on how we implement State pattern  Prepare so we can have fun activity next week