枚举用法报错，说是空指针，不知道为什么,该怎么解决

enum Number { A,two,three,four,five,six,seven,eight,nine,ten,J,Q,K,}enum Color { diamonds,hearts,spade,plum,}class Cards{    public Number number;    public Color color;    public Cards(Number number,Color color){        this.number = number;        this.color = color;    }}public class Pocker {    private Cards []card;    private int deck;    public void init(int n){        if(n<1)            deck=1;        else            deck = n;        card = new Cards[n*52];        for(int i=0;i<52*n;++i){            switch(i%13){            case 1:card[i].number = Number.A;break;            case 2:card[i].number = Number.two;break;            case 3:card[i].number = Number.three;break;            case 4:card[i].number = Number.four;break;            case 5:card[i].number = Number.five;break;            case 6:card[i].number = Number.six;break;            case 7:    card[i].number = Number.seven;break;            case 8:card[i].number = Number.eight;break;            case 9:card[i].number = Number.nine;break;            case 10:card[i].number = Number.ten;break;            case 11:card[i].number = Number.J;break;            case 12:card[i].number = Number.Q;break;            case 13:card[i].number = Number.K;break;                    }            switch(i/13){            case 0:card[i].color = Color.hearts;break;            case 1:card[i].color=Color.diamonds;break;            case 2:card[i].color = Color.plum;break;            case 3:card[i].color=Color.spade;break;            default:break;            }        }    }        public void printInfo(){        for(int i=0;i<card.length;++i){            if(i%13==0)                System.out.println();            System.out.println(card[i].color+" "+card[i].number);        }    }    public static void main(String[] args) {        // TODO Auto-generated method stub                Pocker p = new Pocker();        p.init(2);        p.printInfo();    }}