Java ArrayIndexOutOfBoundsException When Trying to Test

Question

I seem to be getting an error with my deck of cards project. I'm trying to print out a shuffled deck of cards and I've had help already, but this error is now stopping me from progressing

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 51
 at Pack.<init>(Pack.java:14)
 at PackTester.main(PackTester.java:14)
Java Result: 1
BUILD SUCCESSFUL (total time: 2 seconds)

  public class Pack {

private PlayingCard[] deck;   // An array of 52 cards, representing the deck.
private int cardsUsed; // How many cards have been dealt from the deck.

/**
* Creating an unshuffled deck of cards
*/
public Pack() {
   deck = new PlayingCard[51]; //Creates an array of 52 playing cards
   int cardCt = 0; // How many cards have been created so far.
   for ( int suit = 0; suit <= 3; suit++ ) { //If a suit is complete, move to the next suit
      for ( int rank = 1; rank <= 14; rank++ ) { //Builds a complete suit
         deck[51] = new PlayingCard(rank, suit);
         cardCt++; //Adds one to the card count
      }
   }
   cardCt = 0;
}

/**
* Shuffling a deck of cards
*/
public void shuffle() {
      // Put all the used cards back into the deck, and shuffle it into
      // a random order.
    for ( int i = 51; i > 0; i-- ) { 
        int rand = (int)(Math.random()*(i+1));
        PlayingCard temp = deck[i];
        deck[i] = deck[rand];
        deck[rand] = temp;
    }
    cardsUsed = 0;
}

public @Override String toString() {

String deckStr = "";

for (int i=0; i<52; i++) {
    deckStr = deckStr + deck[i].toString() + " ";
}

return deckStr;
}
} // end class Pack

And here is the tester class.

public class PackTester {

public static void main(String[] args)
{
    Pack myPack = new Pack();
    myPack.shuffle();
    System.out.println(myPack.toString());
}
}

I just don't know where to go from here so any help would be appreciated.

Consider using Lists and have your PlayingCard class implement the Comparable interface, Then you can easily shuffle the deck by calling Collections.shuffle(myCardList) — Johan Prins, Feb 23 '15 at 11:54

Eran · Accepted Answer · 2021-06-29T14:03:02.413

0

In order to create a Deck of 52 cards you need :

deck = new PlayingCard[52];

In addition, it makes little sense for your loop to always assign a card to the 51st position :

deck[51] = new PlayingCard(rank, suit);

This would make more sense :

public Pack() {
   deck = new PlayingCard[52]; //Creates an array of 52 playing cards
   int cardCt = 0; // How many cards have been created so far.
   for ( int suit = 0; suit <= 3; suit++ ) { //If a suit is complete, move to the next suit
      for ( int rank = 1; rank < 14; rank++ ) { //Builds a complete suit
         deck[cardCt] = new PlayingCard(rank, suit);
         cardCt++; //Adds one to the card count
      }
   }
}

Also note that there should be 13 ranks, not 14.

edited Jun 29 '21 at 14:03

answered Feb 23 '15 at 10:50

Eran

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Still receiving the same error – Ben Parry Feb 23 '15 at 10:55
@BenParry You can't be getting the `java.lang.ArrayIndexOutOfBoundsException: 51` error if you changed the length of your array to 52. Either you didn't change it, or you are getting a different error. – Eran Feb 23 '15 at 10:57
It is though, I've changed 51 to 52, I'm getting the same error, but the number is 52 now – Ben Parry Feb 23 '15 at 11:01
@BenParry Did you change the condition of the inner loop to `rank < 14`? If not, you are creating too many cards, and there's not enough room for them in your array. – Eran Feb 23 '15 at 11:03
Thanks for the help, just had another problem, but it's been resolved now and the program works – Ben Parry Feb 23 '15 at 11:07

score 0 · Answer 2 · answered Feb 23 '15 at 10:50

You defined array as:

deck = new PlayingCard[51];

And you are trying to add element like:

deck[51] = new PlayingCard(rank, suit);

You are trying to set 51st index element in an array.

Also in shuffle method:

for ( int i = 51; i > 0; i-- ) { //either start with 50 or define array as PlayingCard[52]
int rand = (int)(Math.random()*(i+1));
 PlayingCard temp = deck[i];

Remember index of an array starts from 0 and goes up til n -1, so you need 52nd element (52 cards, i.e. 52nd would be accessed by index 51), increase the array capacity from 51 to 52 when you define the array.

Java ArrayIndexOutOfBoundsException When Trying to Test

2 Answers2