Shuffling a deck of cards

**aterrorbite** · October 5th, 2013, 06:50 PM

I'm not sure why my original deck of cards is shuffling.

public class Cards {
 
    public static void main(String[] agrs){
 
        final String[] standardDeck = {"AC","2C","3C","4C","5C","6C","7C","8C","9C","10C","JC","QC","KC",
                "AD","2D","3D","4D","5D","6D","7D","8D","9D","10D","JD","QD","KD",
                "AH","2H","3H","4H","5H","6H","7H","8H","9H","10H","JH","QH","KH",
                "AS","2S","3S","4S","5S","6S","7S","8S","9S","10S","JS","QS","KS",
        };
 
        String[] shuffledDeck=standardDeck;
 
        int r =0;
        for(int i=0;i<shuffledDeck.length;i++){
           r=(int)(Math.random()*shuffledDeck.length);
           String tempString=shuffledDeck[i];
           shuffledDeck[i]=shuffledDeck[r];
           shuffledDeck[r]=tempString;
        }
 
        for(int i=0;i<shuffledDeck.length;i++){
            System.out.println(standardDeck[i]+"  "+shuffledDeck[i]);
        }
    }
}

I believe that there is something wrong with this section of the code but I don't see it.

int r =0;
        for(int i=0;i<shuffledDeck.length;i++){
           r=(int)(Math.random()*shuffledDeck.length);
           String tempString=shuffledDeck[i];
           shuffledDeck[i]=shuffledDeck[r];
           shuffledDeck[r]=tempString;
        }

My output is:

10D  10D
3C  3C
5D  5D
8S  8S
2H  2H
4S  4S
9S  9S
6S  6S
7S  7S
KC  KC
7C  7C
QH  QH
QD  QD
4H  4H
9D  9D
3D  3D
JD  JD
QC  QC
6C  6C
KD  KD
10H  10H
7H  7H
3H  3H
6D  6D
6H  6H
AD  AD
JS  JS
8D  8D
9H  9H
2C  2C
4C  4C
5H  5H
9C  9C
5S  5S
5C  5C
JC  JC
8C  8C
KH  KH
AS  AS
2S  2S
QS  QS
10C  10C
2D  2D
AH  AH
3S  3S
4D  4D
10S  10S
AC  AC
KS  KS
7D  7D
8H  8H
JH  JH

The first column should be not be shuffled but it is. What am I doing wrong?

**camel-man** · October 5th, 2013, 07:00 PM

String[] shuffledDeck=standardDeck;
I believe that this statement points shuffledDeck to standardDeck and therefore whatever changes in shuffled deck changes in standard. Notice how when you print the columns it should come out in the order you intended for the first column.

Edit: Try this instead

String[] shuffledDeck = standardDeck.clone();

**GoodbyeWorld** · October 5th, 2013, 07:40 PM

Originally Posted by camel-man

String[] shuffledDeck=standardDeck;
I believe that this statement points shuffledDeck to standardDeck and therefore whatever changes in shuffled deck changes in standard. Notice how when you print the columns it should come out in the order you intended for the first column.

Edit: Try this instead

String[] shuffledDeck = standardDeck.clone();

Not sure if that'll work either. I'm not sure what class, if any, handles arrays, but I would think that having an array call the clone method, unless arrays have some special override to Object's clone method that I'm not aware of, would make a shallow copy like Object's clone method does, which is basically what the OP already had. A shallow copy refers to the same memory address and hence would change both when you change one of them.

This code definitely makes a deep, or separate, copy:

String[] shuffledDeck = new String[standardDeck.length];
 
for (int i =0; i < shuffledDeck.length; i++)
{
shuffledDeck[i] = standardDeck[i];
 
 
}

**aterrorbite** · October 5th, 2013, 07:44 PM

Originally Posted by camel-man

String[] shuffledDeck=standardDeck;
I believe that this statement points shuffledDeck to standardDeck and therefore whatever changes in shuffled deck changes in standard. Notice how when you print the columns it should come out in the order you intended for the first column.

Edit: Try this instead

String[] shuffledDeck = standardDeck.clone();

Thanks, that solved it.

I also got it to work with the code shown below.

 String[] shuffledDeck= new String[standardDeck.length];
        for(int i =0;i<standardDeck.length;i++){
            shuffledDeck[i] = new String(standardDeck[i]);
        }

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