Design Lesson 2

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Object-Oriented Design

Given a technical/real-world problem
Simplify to basic parts
Sketch out the classes and methods
Think like a designer for a game

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4 Steps

Clarify the question
Start with main objects
Try link them up
Action with examples

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Clarify the Question

Interviewer is hiding the detail
Ask like a co-worker
who, where, when, why, how, what
1. Internal/External/International user
2. FE/BE
3. Rush hour? Flat? Normal distributed?
4. Current solution not good enough
5. How would you like to implement
6. What's the specific requirement

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Start with Main Objects

Consider the main parts
"Design a Parking Lot"
- Parking Lot
  - Controller
  - ParkingSpace
    - RegularParkingSpace
    - HandicappedParkingSpace
    - CompactParkingSpace
    - EV, RV, ExpectedMother, Truck
  - Car, Sign, Floor, Parker, PayStation, Valet

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Try Link Them Up

Relationship between objects
Member of.
Inherit & Implement

ParkingLot should have an array of Floors
Floor should have an array of ParkingSpace
RegularPS, CompactPS, HandicappedPS... inherit from ParkingSpace
Sign should be Enum: Full, Empty, Invalid

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Action with Examples

Already have the basic outline of your design
Take a example and walk through
Consider the key actions
Update the design if forgot any object

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SpaceController
- assignSpace
- getCar
Floor
- getVacantSpace#
- isFull

Space
- sign
- type
Car
- Plate#
- type

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Design Blackjack (21 点)

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Design Blackjack

Clarify the question
Start with main objects
Try link them up
Action with examples

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BlackJack: A + FaceCard

21: All cards add up to 21

No Joker

Clarify the Question

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Deck
Card -> BJCard
Suit
Player(Hand) -> BJHand
Dealer (Automator)
MainMethodClass

(Heat, Spade, Club, Diamond)

Start with Main Objects

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Try Link Them Up

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Deck
1. Shuffle
2. DealCards
Card -> BJCard
1. Value (Min/Max)
2. Suit
3. isFaceCard
Player(Hand) -> BJHand
1. addCard
2. getScore
3. isBusted
4. isBlackJack

Action with Examples

Dealer (Automator)
1. init (Deck/Hand)
2. getBlackJack
3. playHand
4. getWinner
MainMethodClass
1. init
2. if (hasBJ)
3. else (playHand)
4. getWinner

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import java.util.ArrayList;

public class Main {
    
    public static void main(String[] args) {
        int numHands = 8;
        
        BlackJackGameAutomator automator = new BlackJackGameAutomator(numHands);
        automator.initializeDeck();
        boolean success = automator.dealInitial();
            if (!success) {
                System.out.println("Error. Out of cards.");
            } else {
            System.out.println("-- Initial --");
            automator.printHandsAndScore();
            ArrayList<Integer> blackjacks = automator.getBlackJacks();
            if (blackjacks.size() > 0) {
                System.out.print("Blackjack at ");
                for (int i : blackjacks) {
                    System.out.print(i + ", ");
                }
                System.out.println("");
            } else {
                success = automator.playAllHands();
                if (!success) {
                    System.out.println("Error. Out of cards.");
                } else {
                    System.out.println("\n-- Completed Game --");
                    automator.printHandsAndScore();
                    ArrayList<Integer> winners = automator.getWinners();
                    if (winners.size() > 0) {
                        System.out.print("Winners: ");
                        for (int i : winners) {
                            System.out.print(i + ", ");
                        }
                        System.out.println("");
                    } else {
                        System.out.println("Draw. All players have busted.");
                    }
                }
            }
        }
    }

}

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import java.util.ArrayList;

public class BlackJackGameAutomator {
    private Deck<BlackJackCard> deck;
    private BlackJackHand[] hands;
    private static final int HIT_UNTIL = 16;
    
    public BlackJackGameAutomator(int numPlayers) {
        hands = new BlackJackHand[numPlayers];
        for (int i = 0; i < numPlayers; i++) {
            hands[i] = new BlackJackHand();
        }
    }
    
    public void initializeDeck() {
        ArrayList<BlackJackCard> cards = new ArrayList<BlackJackCard>();
        for (int i = 1; i <= 13; i++) {
            for (int j = 0; j <= 3; j++) {
                Suit suit = Suit.getSuitFromValue(j);
                BlackJackCard card = new BlackJackCard(i, suit);
                cards.add(card);
            }
        }
        deck = new Deck<BlackJackCard>();
        deck.setDeckOfCards(cards);
        deck.shuffle();
    }

    public boolean dealInitial() {
        for (BlackJackHand hand : hands) {
            BlackJackCard card1 = deck.dealCard();
            BlackJackCard card2 = deck.dealCard();
            if (card1 == null || card2 == null) {
                return false;
            }
            hand.addCard(card1);
            hand.addCard(card2);    
        }
        return true;
    }
    
    public ArrayList<Integer> getBlackJacks() {
        ArrayList<Integer> winners = new ArrayList<Integer>();
        for (int i = 0; i < hands.length; i++) {
            if (hands[i].isBlackJack()) {
                winners.add(i);
            }
        }
        return winners;
    }
    
    public boolean playAllHands() {
        for (BlackJackHand hand : hands) {
            if (!playHand(hand)) {
                return false;
            }
        }
        return true;
    }

    public boolean playHand(BlackJackHand hand) {
        while (hand.score() <= HIT_UNTIL) {
            BlackJackCard card = deck.dealCard();
            if (card == null) {
                return false;
            }
            hand.addCard(card);
        }
        return true;
    }    

    public ArrayList<Integer> getWinners() {
        ArrayList<Integer> winners = new ArrayList<Integer>();
        int winningScore = 0;
        for (int i = 0; i < hands.length; i++) {
            BlackJackHand hand = hands[i];
            if (!hand.busted()) {
                if (hand.score() > winningScore) {
                    winningScore = hand.score();
                    winners.clear();
                    winners.add(i);
                } else if (hand.score() == winningScore) {
                    winners.add(i);
                }
            }
        }
        return winners;
    }
    
    public void printHandsAndScore() {
        for (int i = 0; i < hands.length; i++) {
            System.out.print("Hand " + i + " (" + hands[i].score() + "): ");
            hands[i].print();
            System.out.println("");
        }
    }
}

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public abstract class Card {
    private boolean available = true;

    protected int faceValue;
    protected Suit suit;

    public Card(int c, Suit s) {
        faceValue = c;
        suit = s;
    }
    
    public abstract int value();
    
    public Suit suit() { 
        return suit; 
    }
    
    public boolean isAvailable() {
        return available;
    }
    
    public void markUnavailable() {
        available = false;
    }
    
    public void markAvailable() {
        available = true;
    }
    
    public void print() {
        switch (suit) {
        case Club:
            System.out.print("♣");
            break;
        case Heart:
            System.out.print("♥");
            break;
        case Diamond:
            System.out.print("♦");
            break;
        case Spade:
            System.out.print("♠");
            break;            
        }
        String[] faceValues = {"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"};
        System.out.print(faceValues[faceValue - 1]);
        System.out.print(" ");
    }
}

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public enum Suit { 
    Club (0),
    Diamond (1),
    Heart (2),
    Spade (3);
    
    private int value;
    private Suit(int v) {
        value = v;
    }
    
    public int getValue() {
        return value;
    }
    
    public static Suit getSuitFromValue(int value) {
        switch (value) {
        case 0:
            return Suit.Club;
        case 1:
            return Suit.Diamond;
        case 2:
            return Suit.Heart;
        case 3: 
            return Suit.Spade;
        default:
                return null;
        }
    }
}

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public class BlackJackCard extends Card {
    public BlackJackCard(int c, Suit s) {
        super(c, s);
    }
    
    public int value() {
        if (faceValue >= 11 && faceValue <= 13) { // Face card
            return 10;
        } else { // Number card
            return faceValue;
        }
    }
    
    public int minValue() {
        return isAce() ? 1 : value();
    }
    
    public int maxValue() {
        return isAce() ? 11 : value();
    }
    
    public boolean isAce() { 
        return faceValue == 1;
    } 
    
    public boolean isFaceCard() {
        return faceValue >= 11 && faceValue <= 13;
    }
}

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import java.util.ArrayList;

public class Deck <T extends Card> {
    private ArrayList<T> cards;
    private int dealtIndex = 0; // marks first undealt card
    
    public void setDeckOfCards(ArrayList<T> deckOfCards) {
        cards = deckOfCards;
    }
    
    public void shuffle() {
        for (int i = 0; i < cards.size(); i++) {
            int j = randomIntInRange(i, cards.size() - i - 1);
            T card1 = cards.get(i);
            T card2 = cards.get(j);
            cards.set(i, card2);
            cards.set(j, card1);
        }
    }
    
    public T dealCard() {
        if (remainingCards() == 0) {
            return null;
        }
        T card = cards.get(dealtIndex);
        card.markUnavailable();
        dealtIndex++;
        return card;        
    }
    
    public void print() {
        for (T card : cards) {
            card.print();
        }
    }

    private int randomIntInRange(int min, int max) {
        int diff = max - min + 1;
        return (int) (Math.random() * diff) + min;
    }
    
    private int remainingCards() {
        return cards.size() - dealtIndex;
    }
}

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import java.util.ArrayList;

public class Hand <T extends Card> {
    protected ArrayList<T> cards = new ArrayList<T>();
    
    public int score() {
        int score = 0;
        for (T card : cards) {
            score += card.value();
        }
        return score;
    }
    
    public void addCard(T card) {
        cards.add(card);
    }    
    
    public void print() {
        for (Card card : cards) {
            card.print();
        }
    }    
}

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import java.util.ArrayList;

public class BlackJackHand extends Hand<BlackJackCard> {
    
    public int score() {
        ArrayList<Integer> scores = possibleScores();
        int maxUnder = Integer.MIN_VALUE;
        int minOver = Integer.MAX_VALUE;
        for (int score : scores) {
            if (score > 21 && score < minOver) {
                minOver = score;
            } else if (score <= 21 && score > maxUnder) {
                maxUnder = score;
            }
        }
        return maxUnder == Integer.MIN_VALUE ? minOver : maxUnder;
    }
    
    private ArrayList<Integer> possibleScores() {
        ArrayList<Integer> scores = new ArrayList<Integer>();
        if (cards.size() == 0) {
            return scores;
        }
        for (BlackJackCard card : cards) {
            addCardToScoreList(card, scores);
        }
        return scores;
    }
    
    private void addCardToScoreList(BlackJackCard card, ArrayList<Integer> scores) {
        if (scores.size() == 0) {
            scores.add(0);
        } 
        int length = scores.size();
        for (int i = 0; i < length; i++) {
            int score = scores.get(i);
            scores.set(i, score + card.minValue());
            if (card.minValue() != card.maxValue()) {
                scores.add(score + card.maxValue());
            }
        }
    }
    
    public boolean busted() {
        return score() > 21;
    }
    
    public boolean is21() {
        return score() == 21;
    }
    
    public boolean isBlackJack() {
        if (cards.size() != 2) {
            return false;
        }
        BlackJackCard first = cards.get(0);
        BlackJackCard second = cards.get(1);
        return first.isAce() && second.isFaceCard() || second.isAce() && first.isFaceCard();
    }
}

Design Lesson 2

Object-Oriented Design

4 Steps

Clarify the Question

Start with Main Objects

Try Link Them Up

Action with Examples

Design Blackjack (21 点)

Design Blackjack

Clarify the Question

Start with Main Objects

Try Link Them Up

Action with Examples

[GoValley-201612] Design Lesson 3 OO Design

[GoValley-201612] Design Lesson 3 OO Design

govalley201612

Design Lesson 2

Object-Oriented Design

4 Steps

Clarify the Question

Start with Main Objects

Try Link Them Up

Action with Examples

Design Blackjack (21 点)

Design Blackjack

Clarify the Question

Start with Main Objects

Try Link Them Up

Action with Examples

[GoValley-201612] Design Lesson 3 OO Design

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