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Thread: Shuffling a deck

  1. #1
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    Default Shuffling a deck

    So I have all this made.. and I need to shuffle the deck, but it's not working and it's getting on my nerves...

     
    import java.util.*;
     
    class Hand { 
        static Card[] deck = new Card[52];
        Card[] hand = new Card[10];
        static int index;
     
     
     
     
        public static void createDeck () {
            int m = 0;
            for (int j = 0; j < 4; j++) {
                for (int k = 1; k < 14; k++) {
                   deck[m] = new Card(j,k);
                   m++;
                }
            }
            index = 0;
        } //end createDeck
     
        public static Card deal () {
            index++;
            return deck[index-1];
        } //end deal
     
     
     
        public static int compareCard (Card c1, Card c2) {     
            if (c1.getSuit() > c2.getSuit()) return 1; 
            if (c1.getSuit() < c2.getSuit()) return -1;
            if (c1.getRank() > c2.getRank()) return 1; 
            if (c1.getRank() < c2.getRank()) return -1;
            return 0;
        } //end compareCard
     
        public void printDeck (int size) {
            int j = 0;
            while (j < size) {
                deck[j].printCard();
                j++;
            }
        }//end printDeck
     
        public void shuffleDeck () {
             Random randomNumber = new Random ();
     
            for (int i =0; i < deck.length; i++) {
                int randomInt = randomNumber.nextInt (53);
              Card temp = hand [i];
               hand[i] = hand [randomInt];
               hand[randomInt] = temp;
     
        }
    }//end shuffleDeck
     
    } //end class
    Last edited by Darkzama; June 11th, 2013 at 05:38 PM. Reason: I edited the shuffle.. works a little better. still an error when run


  2. #2
    Super Moderator pbrockway2's Avatar
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    Default Re: Shuffling a deck

    it's not working
    So, what is the problem? Does the code compile? If it does compile, does it do something unwanted or unexpected at runtime? If so, what?

  3. #3
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    Default Re: Shuffling a deck

    It compiles, but when I run the Driver, it gives me an array exception...
    Untitled.jpg

    there's a screen shot of my error

  4. #4
    Super Moderator pbrockway2's Avatar
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    Default Re: Shuffling a deck

    Sorry, I can't read the image.

    What is the stack trace? (the thing that says what the exception is, and then gives a list of lines of your code to go looking at)

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    Default Re: Shuffling a deck

    it says "Java.lang.ArrayIndexOutofboundsexcetion: ## (the number changes each time it's run)
    at hand.shuffleDeck (hand.java:52)
    at Dealer.<init>(Dealer.java:11)
    at Driver.Main(Driver.java:3)

    and then in my code it highlights "Hand[I] = hand [randomInt];"

  6. #6
    Super Moderator pbrockway2's Avatar
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    Default Re: Shuffling a deck

    OK.

    You read these stack traces from the top down, until you reach a line of your code (which happens rather soon here!). It is saying that the problem is an ArrayIndexOutOfBoundsException. In other words you are trying to access an array at a crazy place (say a negative index, or an index that is too big.)

    That ## number is the crazy index that the Java runtime is complaining about. Not all exception messages are as helpful.

    Now the problem is evidently occurring at the line "hand[i] = hand [randomInt];" which is line 52 of the file Hand.java.

    The first thing to do is have a look where the hand array is initialised. That's up near the top:

    Card[] hand = new Card[10];

    So hand is an array that holds exactly ten cards. But back where the problem is occuring you say:

    int randomInt = randomNumber.nextInt (53);
    Card temp = hand [i];
    hand[i] = hand [randomInt];

    If randomInt is ever bigger than nine (and it very well may be) then you will get an ArrayIndexOutOfBoundsException.

    Basically the hand is too small (ten elements) for what you are shuffling (a random thing 0->52). I wonder if you mean to shuffle the hand or the deck...
    Last edited by pbrockway2; June 11th, 2013 at 06:17 PM. Reason: too many typos :( and I was trying hard to get things precise...

  7. The Following User Says Thank You to pbrockway2 For This Useful Post:

    Darkzama (June 11th, 2013)

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    Default Re: Shuffling a deck

    Okay... so, I reduced the random int to 9... and I still got the same error, but on the line above where it was before... and I mean to shuffle the deck....
    *edit*
    I got it.. thanks very much pbrockway!

  9. #8
    Super Moderator pbrockway2's Avatar
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    Default Re: Shuffling a deck

    You're welcome.

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