Java数组,NullPointerException？

Question

我宣布两张牌:

Card card1 = new Card('3', Card.Suit.clubs);
Card card2 = new Card('T', Card.Suit.diamonds);

这有效:

Hand hand1 = new Hand();

hand1.takeCard(card1);

但为什么这不起作用？它在第二行给我一个NullPointerException:

Hand[] hand = new Hand[2];

hand[0].takeCard(card2);

Answer 1

你正在宣布一组2手牌.这只是设置数组.然后,您需要实例化数组中的手对象.

说

hand[0] = new Hand(); 
hand[1] = new Hand();