在一個toString類Return語句

Question

所以我有一個卡類，看起來像這樣：

public class Card 
{ 
    //instance variables 
    private String faceValue; //the face value of the card 
    private String suit; //the suit of the card 
    String[] ranks = {"Ace", "2", "3", "4", "5", "6","7", "8", "9", "10", "Jack", "Queen", "King"}; 
    String[] suits = {"Clubs", "Diamonds", "Hearts", "Spades"}; 

/** 
* Constructor 
*/ 
public Card(int aValue, int aSuit) 
{ 
    faceValue = ranks[aValue]; 
    suit = suits[aSuit]; 
} 

//getters 
/** 
* Getter for faceValue. 
*/ 
public String getFaceValue() 
{ 
    return faceValue; 
} 

/** 
* Getter for suit. 
*/ 
public String getSuit() 
{ 
    return suit; 
} 
//end of getters 

//methods 
/** 
* This method returns a String representation of a Card object. 
* 
* @param none 
* @return String 
*/ 
public String toString() 
{ 
    return "A card: " + faceValue + " of " + suit; 
} 
} 

而且甲板類，看起來像這樣：在甲板上表演

public class Deck 
{ 
    //instance variables 
    private Card[] deck; 

/** 
* Constructor for objects of class Deck 
*/ 
public Deck() 
{ 
    deck = new Card[52]; 

    int cardCount = 0; //number of cards created so far. 
    for (int aSuit = 0; aSuit < 4; aSuit++) 
    { 
     for (int aValue = 0; aValue < 13; aValue++) { 
      deck[cardCount] = new Test(aValue, aSuit); 
      cardCount++; 
     } 
    } 
} 

/** 
* String representation. 
*/ 
public String toString() 
{ 
    for (int i = 0; i < 52; i++) 
    { 
     String v = deck[i].getFaceValue(); 
     String s = deck[i].getSuit(); 
     return "Dealt a card: " + v + " of " + s + "."; 
    } 
} 
} 

我的toString方法錯誤「缺少返回語句」。如何更改退貨聲明，同時仍然允許它在每次循環後打印卡片細節？

Answer 1

你寫的代碼只會從deck數組中返回第0個元素。它應該是這樣的：

public String toString() 
{ 
    StringBuilder sb = new StringBuilder(); 
    for (int i = 0; i < 52; i++) 
    { 
     String v = deck[i].getFaceValue(); 
     String s = deck[i].getSuit(); 
     sb.append("Dealt a card: ").append(v).append(" of ").append(s).append(".\n"); 
    } 
    return sb.toString(); 
} 

Answer 2

錯誤是因爲您的toString方法具有返回類型String。
Java檢查執行路徑。如果for循環結束並且永不返回任何內容會怎麼樣？

儘管您可能已對該邏輯進行了硬編碼，但Java編譯器並未對此進行統計分析。因此它必須返回一個字符串，如果沒有其他的工作，它肯定會執行。

這將工作：

public String toString() 
{ 
    for (int i = 0; i < 52; i++) 
    { 
     String v = deck[i].getFaceValue(); 
     String s = deck[i].getSuit(); 
     return "Dealt a card: " + v + " of " + s + "."; 
    } 
    return ""; 
} 

但我猜你想要的東西是這樣的：

public String toString() 
{ 
    StringBuilder returnValue = new StringBuilder(""); 
    for (int i = 0; i < 52; i++) 
    { 
     String v = deck[i].getFaceValue(); 
     String s = deck[i].getSuit(); 
     returnValue.append("Dealt a card: " + v + " of " + s + "."); 
    } 
    return returnValue.toString(); 
} 

Answer 3

如果u只想打印所有卡的相關信息，u可以使用

public String toString(){ 
    for (int i = 0; i < 52; i++) 
    { 
    String v = deck[i].getFaceValue(); 
    String s = deck[i].getSuit(); 
    System.out.println("Dealt a card: " + v + " of " + s + "."); 
    } 
    return null; 
}