我洗牌的想法是生成一个随机数，然后在cardsToSelect这个List里面在该随机数的位置把元素取出来按顺序放进新建的List——washedList里面。
我想打印一下输出看看有没有成功，就报错Exception in thread "main" java.lang.NullPointerException
该怎么解决？
代码在下面
谢谢
cardsToSelect是什么？初始化了吗
public void washCard() {
int size = cardsToSelect.size();
List<Card> washedList = new ArrayList<Card>();
for (int i = 0; i < size; i++) {
Card temp = new Card();
do {
temp = cardsToSelect.get(random.nextInt(size));
} while (washedList.contains(temp));
washedList.add(temp);
}
System.out.println("==========洗牌后==========");
for (int i = 0; i < size; i++) {
System.out.print(washedList.get(i).type
+ washedList.get(i).num + ",");
}
}