是什麼給我這個錯誤？

Question

這是我的學校項目中的撲克遊戲。我有一些例外，我無法弄清楚。

在開始時，我定義了卡類。

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]; } 


/* Few quick tests here */ 
public static void main(String args[]) 
{ 
try { 
    Card c1 = new Card(1,3); // A Spades 
    System.out.println(c1); 
    c1 = new Card(10,0); // 10 Clubs 
    System.out.println(c1); 
    c1 = new Card(10,5);  // generate exception here 
} 
catch (MyPlayingCardException e) 
{ 
    System.out.println("MyPlayingCardException: "+e.getMessage()); 
} 
} 

}

我創建了這個類的異常。然後，在我的Decks類中，我繼續從Deck構造函數中獲取異常錯誤。

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); 

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

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

       Card card = new Card(j,i); 
       originalDecks.add(card); 
      }    
     } 

    dealDecks.addAll(originalDecks); 


} 

爲什麼？如果我使用我的實例卡是從for循環（這意味着他們我< 3，j < 13），爲什麼我仍然得到異常錯誤？

unreported exception MyPlayingCardException; must be caught or declared to be thrown 
       Card card = new Card(j,i); 

Answer 1

在java中，你必須處理，不同的是你的代碼威力拋出。這個編譯器錯誤是說你的Card構造函數可以拋出MyPlayingCardException類型的異常，但是你的Deck構造函數沒有處理它。這裏有兩種方法。你可以改變你的Decks構造函數讀取

public Decks() throws MyPlayingCardException 
{ 
    //constructor code here 
} 

，或者你可以處理這樣

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

      try 
      { 
      Card card = new Card(j,i); 
      originalDecks.add(card); 
      } 
      catch(MyPlayingCardException ex){ 
       //some code to handle MyPlayingCardException here 
      } 
     }    
    } 

Answer 2

在java中的例外，那就是通過一個方法或接口中聲明必須處理的一個例外，無論是抓住它或傳遞給下一個級別。在你的代碼中，Card()構造函數拋出異常。你的Decks()構造函數創建卡片，但不抓住或拋出卡片例外。