问题和练习

• 问题
• 练习

问题

1. 考虑以下两个类

public class ClassA {
    public void methodOne(int i) {
    }
    public void methodTwo(int i) {
    }
    public static void methodThree(int i) {
    }
    public static void methodFour(int i) {
    }
}

public class ClassB extends ClassA {
    public static void methodOne(int i) {
    }
    public void methodTwo(int i) {
    }
    public void methodThree(int i) {
    }
    public static void methodFour(int i) {
    }
}

• a. 哪个方法重写超类中的方法？

  答：methodTwo

• b. 哪个方法在超类中隐藏一个方法？

  答：methodFour

• c. 其他方法有什么作用？

  答：他们导致编译时错误

2. 考虑 Card， Deck 以及 DisplayDeck 类你写的问题和练习类。每个类应该覆盖 Object 哪些方法？

   答：Card 和 Deck 应重写 equals、hashCode 和 toString。

练习

编写您在问题 2 中回答的方法的实现。

public class Card2 {
    private int rank;
    private int suit;

    public final static int DIAMONDS = 1;
    public final static int CLUBS = 2;
    public final static int HEARTS = 3;
    public final static int SPADES = 4;

    public final static int ACE = 1;
    public final static int DEUCE = 2;
    public final static int THREE = 3;
    public final static int FOUR = 4;
    public final static int FIVE = 5;
    public final static int SIX = 6;
    public final static int SEVEN = 7;
    public final static int EIGHT = 8;
    public final static int NINE = 9;
    public final static int TEN = 10;
    public final static int JACK = 11;
    public final static int QUEEN = 12;
    public final static int KING = 13;

    public Card2(int rank, int suit) {
        this.rank = rank;
        this.suit = suit;
    }

    public int getSuit() {
        return suit;
    }

    public int getRank() {
        return rank;
    }

    public static boolean isValidRank(int rank) {
        return ACE <= rank && rank <= KING;
    }

    public static boolean isValidSuit(int suit) {
        return DIAMONDS <= suit && suit <= SPADES;
    }

    public boolean equals(Object obj) {
        if (obj instanceof Card2) {
            if (((Card2)obj).getRank() == this.rank &&
                ((Card2)obj).getSuit() == this.suit) {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    public int hashCode() {
        return ((suit-1)*13)+rank;
    }

    public String toString() {
        return rankToString(this.rank) + " of "
               + suitToString(this.suit);
    }

    public static String rankToString(int rank) {
        switch (rank) {
            case ACE:
                return "Ace";
            case DEUCE:
                return "Deuce";
            case THREE:
                return "Three";
            case FOUR:
                return "Four";
            case FIVE:
                return "Five";
            case SIX:
                return "Six";
            case SEVEN:
                return "Seven";
            case EIGHT:
                return "Eight";
            case NINE:
                return "Nine";
            case TEN:
                return "Ten";
            case JACK:
                return "Jack";
            case QUEEN:
                return "Queen";
            case KING:
                return "King";
            default:
                //Handle an illegal argument.  There are generally two ways
                //to handle invalid arguments, throwing an exception (see
                //the section on Handling Exceptions):
                throw new IllegalArgumentException("Invalid rank " + rank);
                //or
                //return null;
        }
    }

    public static String suitToString(int suit) {
        String result = "";
        switch (suit) {
            case DIAMONDS:
                return "Diamonds";
            case CLUBS:
                return "Clubs";
            case HEARTS:
                return "Hearts";
            case SPADES:
                return "Spades";
            default:
                throw new IllegalArgumentException("Invalid suit " + suit);
        }
    }

    public static void main(String... args) {
        new Card2(ACE, DIAMONDS);
        new Card2(KING, SPADES);
    }
}