I want to draw a random card from a deck and validates that it's always unique. I'm using the cardGenerator() recursive function to do that. If the random card picked has been shown then it calls itself again. Need a work around or if any of yall got a better logic please let me know.

import java.util.ArrayList;
import java.util.Random;

public class App {
    static ArrayList<Integer[]> deck = new ArrayList<>();
    static ArrayList<Integer[]> dealer = new ArrayList<>();

    static Integer[] cardGenerator() throws Exception{
        Random random = new Random();
        Integer[] card = {0, 0};
        Integer num = random.nextInt(13);
        Integer shape = random.nextInt(4);
        Integer[] deckSet = deck.get(num);
        if(deckSet[shape] == 1){
            deckSet[shape] = 0;
            deck.set(num, deckSet);
            card[0] = num;
            card[1] = shape;
            return card;
        }
        else return cardGenerator();
    }

    public static void main(String[] args) throws Exception {
        Integer[] deckSet = {1, 1, 1, 1};
        for(int i = 0; i < 13; i  ){
            deck.add(deckSet);
        }
        dealer.add(cardGenerator());
        dealer.add(cardGenerator());
        dealer.add(cardGenerator());
        dealer.add(cardGenerator());
        dealer.add(cardGenerator());
    }
}

expecting for dealer to store 5 unique cards, but java.lang.StackOverflowError occured on the cardGenerator function.

CodePudding user response：

You use the same deckSet array for all deck numbers. That means that after drawing for cards for all deck numbers the deckSet will be {0, 0, 0, 0}.

To solve it you need to initialize the deck as

    for(int i = 0; i < 13; i  ){
        Integer[] deckSet = {1, 1, 1, 1};
        deck.add(deckSet);
    }

CodePudding user response：

You need to make a new array for each element of the ArrayList, or else every element in the ArrayList is pointing to the same array. So for each of the 4 draws, it will turn 1 number in { 1, 1, 1, 1 } into 0, and on the 5th draw, a stack overflow occurs as there is no more 1s in the shared array.

You can fix the code by moving the new array declaration inside the loop, so a new array is created to be added to the list:

        for(int i = 0; i < 13; i  ){
            Integer[] deckSet = {1, 1, 1, 1}; // Moved inside
            deck.add(deckSet);
        }

Doesn't seem like you initialized all the Integers in the arrays in deck to be 1, so the conditional in the if statement is always false.

        if(deckSet[shape] == 0){ // Zero for unpicked card
            deckSet[shape] = 1; // One for picked card
            deck.set(num, deckSet);
            card[0] = num;
            card[1] = shape;
            return card;
        }