如何在 java 中操作数组

Question

im making a blackjack game in java and I get an initial array of size two. However when I want to twist I want to add another card to the array. However I cannot change its size

 public static void userDrawCards() {
        int min = 1;
        int max = 11;

        int[] cards = new int[2];

        System.out.println("Welcome to BlackJack");

        for (int i = 0; i < cards.length; i++) {
            int random = (int) (Math.random() * (max - min + 1) + min);
            cards[i] = random;
        }
        System.out.println("Your cards are " + Arrays.toString(cards));
    }

Ive checked and it says an arraylist would be better to use. So i try this and im unsure on how to use it when i try i get this

public static void userDrawCards() {
        int min = 1;
        int max = 11;

        List cards = new ArrayList();

        System.out.println("Welcome to BlackJack");

        for (int i = 0; i < cards.size(); i++) {
            int random = (int) (Math.random() * (max - min + 1) + min);
            cards.set(i, random);
        }
        System.out.println("Your cards are " + cards);
    }

Giving me this Your cards are [] as a response. Any help would be great thanks:)

Answer 1

first of all, it's a good practice to add parameter of type you are going to use in your list. In your case cards are ints so use:

    List<Integer> cards = new ArrayList<Integer>();

this creates an empty list, so it's size is 0. That means your for loop is completely skipped. To fix that declare some variable of how many cards you want to have:

final int amountOfCards = 10;
List<Integer> cards = new ArrayList<>(amountOfCards); // argument is optional, this is just for efficiency purposes

Now you can have for loop like this:

for (int i = 0; i <amountOfCards; i++) {

but you can't use set at this point. The list is empty, so if you use set, you are going to get IndexOutOfBoundsException. If you want to add cards, use add :

cards.add(random);

alternatively you can add at position using cards.add([index here], random)