为什么它总是告诉我“变量卡可能没有被初始化”

Question

这是一个java扑克游戏项目。一开始，我定义了卡类。

class Card { 

/* constant suits and ranks */ 
static final String[] Suit = {"Clubs", "Diamonds", "Hearts", "Spades" }; 
static final String[] Rank = {"","A","2","3","4","5","6","7","8","9","10","J","Q","K"}; 

/* Data field of a card: rank and suit */ 
private int cardRank; /* values: 1-13 (see Rank[] above) */ 
private int cardSuit; /* values: 0-3 (see Suit[] above) */ 

/* Constructor to create a card */ 
/* throw MyPlayingCardException if rank or suit is invalid */ 
public Card(int rank, int suit) throws MyPlayingCardException { 
if ((rank < 1) || (rank > 13)) 
    throw new MyPlayingCardException("Invalid rank:"+rank); 
else 
     cardRank = rank; 
if ((suit < 0) || (suit > 3)) 
    throw new MyPlayingCardException("Invalid suit:"+suit); 
else 
     cardSuit = suit; 
} 

/* Accessor and toString */ 
/* You may impelemnt equals(), but it will not be used */ 
public int getRank() { return cardRank; } 
public int getSuit() { return cardSuit; } 
public String toString() { return Rank[cardRank] + " " + Suit[cardSuit]; } 

然后，我试着定义Deck类来持有卡。但是我在Deck构造函数中遇到了问题。它一直告诉我“变量卡可能未被初始化”。我想我已经在构造函数的开头初始化了它。什么给我错误？

class Decks { 

/* this is used to keep track of original n*52 cards */ 
private List<Card> originalDecks; 

/* this starts with n*52 cards deck from original deck */ 
/* it is used to keep track of remaining cards to deal */ 
/* see reset(): it resets dealDecks to a full deck  */ 
private List<Card> dealDecks; 

/* number of decks in this object */ 
private int numberDecks; 


/** 
* Constructor: Creates default one deck of 52 playing cards in originalDecks and 
*   copy them to dealDecks. 
*    initialize numberDecks=n 
* Note: You need to catch MyPlayingCardException from Card constructor 
*  Use ArrayList for both originalDecks & dealDecks 
*/ 
public Decks() 
{ 
    // implement this method! 

    ArrayList<Card> originalDecks = new ArrayList<Card>(52); 
    ArrayList<Card> dealDecks = new ArrayList<Card>(52); 

    Card card; 
    for (int i=1; i<=3; i++) { 

     for (int j=1; j<= 13; j++) { 

      try{ 
       card = new Card(j,i); 
       }catch (MyPlayingCardException e){ 
        System.out.println("MyPlayingCardException: "+e.getMessage()); 
       } 
      originalDecks.add(card); 
      }    
     } 

    dealDecks.addAll(originalDecks); 


} 

/** 
* Constructor: Creates n decks (52 cards each deck) of playing cards in 
*    originalDecks and copy them to dealDecks. 
*    initialize numberDecks=n 
* Note: You need to catch MyPlayingCardException from Card constructor 
*  Use ArrayList for both originalDecks & dealDecks 
*/ 
public Decks(int n) 
{ 
    int numberDecks=n ; 
    Card card; 

    for (int m=0; m<n; m++){ 

     for (int i=0; i<=3; i++) { 

      for (int j=0; j<= 13; j++) { 

       try{ 
        card = new Card(j,i);  
        } 
        catch (MyPlayingCardException e){ 
         System.out.println("MyPlayingCardException: "+e.getMessage()); 
        } 
       originalDecks.add(card); 
      } 
      dealDecks.addAll(originalDecks); 
     } 
    }    

} 

Answer 1

编译器抱怨这条线......

  originalDecks.add(card); 

...它是正确的。

如果Card构造函数抛出一个MyPlayingCardException那么当你第一次尝试初始化card变量，然后控制就会传递到catch块没有card已经初始化。 catch块会打印一条消息，但只允许控制落入该问题的线路。您可以捕获异常并输出消息，但在这种情况下，catch块也必须抛出一个异常（无论是相同还是不同的异常），否则它必须以某种方式初始化card本身。

请注意，如果Card构造函数在内循环的后续迭代中抛出MyPlayingCardException，则card将保留其先前的值。虽然在这种情况下它不会未初始化，但它所具有的价值并不是您实际想要使用的价值。