我正在使用面向對象編程來制作二十一點游戲。到目前為止，我寫的是：import java.util.Random;public class Blackjack {    public static String[] Card = new String[12];    public static String[] Suits = {"D", "H", "S", "C"};    public void setCard(String[] c) {        Card = c;        Card[0] = "A";        Card[1] = "2";        Card[2] = "3";        Card[3] = "4";        Card[4] = "5";        Card[5] = "6";        Card[6] = "7";        Card[7] = "8";        Card[8] = "9";        Card[9] = "10";        Card[10] = "J";        Card[11] = "Q";        Card[12] = "K";    }    public static void main(String[] args) {        System.out.println("Welcome to Blackjack.");        Random rand = new Random();        int card_Sign1 = (int) (Math.random() * 13);        int card_Sign2 = (int) (Math.random() * 13);        int Suit1 = (int) (Math.random() * 4);        int Suit2 = (int) (Math.random() * 4);        System.out.print(Card[card_Sign1]);    }}輸出我得到的是Welcome to Blackjack那么null。我想知道我是否可以在解決該問題上獲得一些幫助。