toString类中的return语句

Question

所以我有一个Card类，看起来像这样：

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;
}
}

还有一个Deck类，如下所示：

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 + ".";
    }
}
} 

我在套牌中的toString方法显示错误“缺少返回语句”。 在每次循环后仍允许其打印卡详细信息的同时，如何更改return语句？

Answer 1

您编写的代码将仅从卡座数组返回第0个元素。 它应该像这样：

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

该错误是因为您的toString方法具有返回类型String。
Java检查执行路径。 如果for循环结束并且从不返回任何内容怎么办？

尽管您可能已经对该逻辑进行了硬编码，但是Java编译器并未对此进行统计分析。 因此，它必须返回String类型，如果没有其他作用，则必须执行。

这将起作用：

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 "";
}

但是我想你想要的是：

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

如果您只想打印所有卡信息，则可以使用

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;
}