Question

我正在尝试将一个简单的插卡放在一起，然后我遇到了NullPointerException，程序编译但是如果我运行它并运行方法setSuit，我收到此错误消息：

java.lang.NullPointerException
  at Cards.setCard(Cards.java:18)
  at Cards.<init>(Cards.java:11)

我发布了以下代码并标记了突出显示的区域：

public class Cards {
    private String HEARTS = "Hearts";
    private String CLUBS = "Clubs";
    private String DIAMONDS = "Diamonds";
    private String SPADES = "Spades";
    private int number;
    private String suit;
    public Cards(String newCard, int newNumber1) {
        setCard(newCard);
        setNumber(newNumber1);
    }

    public void setCard(String newSuit) {
        if((suit != null) && // this part get's highlighted 
          (suit.equalsIgnoreCase(HEARTS)) ||
          (suit.equalsIgnoreCase(DIAMONDS)) ||
          (suit.equalsIgnoreCase(CLUBS))    ||
          (suit.equalsIgnoreCase(SPADES))) {
            suit = newSuit;
        } else {
            suit = "Unknown Suit";
            System.out.print("Invalid");
        }

    }
    public int getNumber() {
         return number;
    }

    public String getSuit() {
         return suit;
    }

    public void setNumber(int newNumber) {
         number = newNumber;
         if(newNumber >0 && newNumber <=10) {
              number = newNumber;
         }
    }
}

Answer 1

这是一个操作顺序问题。试试这个：

if ((suit != null) && (suit.equalsIgnoreCase(HEARTS) || suit.equalsIgnoreCase(DIAMONDS) || suit.equalsIgnoreCase(CLUBS) || suit.equalsIgnoreCase(SPADES)))

Answer 2

检查一下，但我认为setCard应该是：

public void setCard(String newSuit)
    {
    if((newSuit != null) && //this part get's highlighted 
    (newSuit.equalsIgnoreCase(HEARTS)) ||
    (newSuit.equalsIgnoreCase(DIAMONDS)) ||
    (newSuit.equalsIgnoreCase(CLUBS))    ||
    (newSuit.equalsIgnoreCase(SPADES)))
    {
        suit = newSuit;
    }
    else 
    {
        suit = "Unknown Suit";
        System.out.print("Invalid");
    }
}

Bluej空指针异常

2 个答案: