I have an Array List of cards containing 52 cards. I want to shuffle the deck.
This is what I have done.
Here is my code:
String[] Number = {"A","2","3","4","5","6","7","8","9","10","J","Q","K"};
String[] Suits = {"Club","Diamonds","Hearts","Spades"};
ArrayList<Card> deck = new ArrayList<Card>();
// create a deck
for(int i=0;i<13;i++){
for(int j=0;j<4;j++){
Card card = new Card(Suits[j],Number[i]);
deck.add(card);
}
}
// shuffle of deck
ArrayList<Card> new_deck = new ArrayList<Card>();
while(deck.size()!=0){
Random rand = new Random();
int n = rand.nextInt(deck.size());
new_deck.add(deck.get(n));
deck.remove(n);
}
// Display
for(int i=0;i<52;i++){
System.out.println(new_deck.get(i).getSuit()+" : "+new_deck.get(i).getValue());
}
Finally, I get the shuffled deck from new ArrayList.
Is its randomness good enough or not?
What should I do to increase randomness?
Does it's randomness is enough or not ?
Define good enough (!!)
Your current approach is going to give a good shuffle, with no obvious biases ... except for biases that may be introduced by the random number generator.
And in this case, there is real cause for concern. Random is specified to be a linear congruential generator, and LC generations have distinct patterns in the numbers that they generate. (In statistical terms, they show strong auto-correlation.) This is quite clear if you graph the n'th random number against n.
To improve randomness, you should use a better random number generator. The SecureRandom
generator should be good enough: javadoc.
The same concern about the randomness applies if you use Collections.shuffle
method. For a good (or consistent) shuffle you should use the method overload where you supply a Random
implementation ... and choose a good one.