public class DealCard { /**
* @param args
*/
public Map<Integer, String> CardTag = new HashMap<Integer, String>();
public Map<Integer, String> CardNumber = new HashMap<Integer, String>();
//List<Card> card = new ArrayList<Card>();
public DealCard(){
CardTag = put(1, "Spade");
CardTag = put(2, "Heart");
CardTag = put(3, "Club");
CardTag = put(4, "Diamond");
System.out.println(CardTag.size());
}
}
* @param args
*/
public Map<Integer, String> CardTag = new HashMap<Integer, String>();
public Map<Integer, String> CardNumber = new HashMap<Integer, String>();
//List<Card> card = new ArrayList<Card>();
public DealCard(){
CardTag = put(1, "Spade");
CardTag = put(2, "Heart");
CardTag = put(3, "Club");
CardTag = put(4, "Diamond");
System.out.println(CardTag.size());
}
}
* @param args
*/
public Map<Integer, String> CardTag = new HashMap<Integer, String>();
public Map<Integer, String> CardNumber = new HashMap<Integer, String>();
//List<Card> card = new ArrayList<Card>();
public DealCard(){
CardTag = put(1, "Spade");
CardTag = put(2, "Heart");
CardTag = put(3, "Club");
CardTag = put(4, "Diamond");
System.out.println(CardTag.size());//Exception in thread "main" java.lang.NullPointerException
//at DealCard.<init>
}
public static void main(String[] args) {
// TODO Auto-generated method stub
DealCard deal = new DealCard();
}这句不明白 为什么异常了又?
CardTag = put(2, "Heart");
CardTag = put(3, "Club");
CardTag = put(4, "Diamond");
为什么没有写成:
CardTag.put(1, "Spade");
CardTag.put(2, "Heart");
CardTag.put(3, "Club");
CardTag.put(4, "Diamond");
就因为这个原因,你没有在CardTag对象中添加成功,所以程序报空指针异常
在Java程序中,除了静态方法以外,其余的方法都是需要通过对象名点出的.