Java 输出中为Null，而其他输出中没有Null

我在上java初学者课程。我必须制作一张卡片。然后创建一副牌和一些方法，然后进行测试

我的卡片分类如下

import java.util.*;

public class Card
{
   public final static int ACE   = 1;
   public final static int TWO   = 2;
   public final static int THREE = 3;
   public final static int FOUR  = 4;
   public final static int FIVE  = 5;
   public final static int SIX   = 6;
   public final static int SEVEN = 7;
   public final static int EIGHT = 8;
   public final static int NINE  = 9;
   public final static int TEN   = 10;
   public final static int JACK  = 11;
   public final static int QUEEN = 12;
   public final static int KING  = 13;

   public final static int CLUBS    = 1;
   public final static int DIAMONDS = 2;
   public final static int HEARTS   = 3;
   public final static int SPADES   = 4;

   private final static int NUM_FACES = 13;
   private final static int NUM_SUITS = 4;

   private int face, suit;
   private String faceName, suitName;

   private int myInt1, myInt2;

   Random rand = new Random();

   //-----------------------------------------------------------------
   //  Creates a random card.
   //-----------------------------------------------------------------
   public Card ()
   {
      face = rand.nextInt(4) + 1;
      setFaceName();

      suit = rand.nextInt(13) + 1;
      setSuitName();
   }



   //-----------------------------------------------------------------
   //  Sets the string representation of the face using its stored
   //  numeric value.
   //-----------------------------------------------------------------
   private void setFaceName()
   {
      switch (face)
      {
         case 1:
            faceName = "Ace";
            break;
         case 2:
            faceName = "Two";
            break;
         case 3:
            faceName = "Three";
            break;
         case 4:
            faceName = "Four";
            break;
         case 5:
            faceName = "Five";
            break;
         case 6:
            faceName = "Six";
            break;
         case 7:
            faceName = "Seven";
            break;
         case 8:
            faceName = "Eight";
            break;
         case 9:
            faceName = "Nine";
            break;
         case 10:
            faceName = "Ten";
            break;
         case 11:
            faceName = "Jack";
            break;
         case 12:
            faceName = "Queen";
            break;
         case 13:
            faceName = "King";
            break;
      }
   }

   //-----------------------------------------------------------------
   //  Sets the string representation of the suit using its stored
   //  numeric value.
   //-----------------------------------------------------------------
   private void setSuitName()
   {
      switch (suit)
      {
         case 1:
            suitName = "Clubs";
            break;
         case 2:
            suitName = "Diamonds";
            break;
         case 3:
            suitName = "Hearts";
            break;
         case 4:
            suitName = "Spades";
            break;
      }
   }

   //-----------------------------------------------------------------
   //  Determines if this card is higher than the passed card. The
   //  second parameter determines if aces should be considered high
   //  (beats a King) or low (lowest of all faces).  Uses the suit
   //  if both cards have the same face.
   //-----------------------------------------------------------------
   public boolean isHigherThan (Card card2, boolean aceHigh)
   {
      boolean result = false;

      if (face == card2.getFace())
      {
         if (suit > card2.getSuit())
            result = true;
      }
      else
      {
         if (aceHigh && face == ACE)
            result = true;
         else
            if (face > card2.getFace())
               result = true;
      }

      return result;
   }

   //-----------------------------------------------------------------
   //  Determines if this card is higher than the passed card,
   //  assuming that aces should be considered high.
   //-----------------------------------------------------------------
   public boolean isHigherThan (Card card2)
   {
      return isHigherThan (card2, true);
   }

   //-----------------------------------------------------------------
   //  Returns the face (numeric value) of this card.
   //-----------------------------------------------------------------
   public int getFace ()
   {
      return face;
   }

   //-----------------------------------------------------------------
   //  Returns the suit (numeric value) of this card.
   //-----------------------------------------------------------------
   public int getSuit ()
   {
      return suit;
   }

   //-----------------------------------------------------------------
   //  Returns the face (string value) of this card.
   //-----------------------------------------------------------------
   public String getFaceName ()
   {
      return faceName;
   }

   //-----------------------------------------------------------------
   //  Returns the suit (string value) of this card.
   //-----------------------------------------------------------------
   public String getSuitName ()
   {
      return suitName;
   }

   //-----------------------------------------------------------------
   //  Returns the string representation of this card, including
   //  both face and suit.
   //-----------------------------------------------------------------



   public String toString ()
   {
      return getFaceName() + " of " + getSuitName();
   }
}

import java.util.*;


public class DeckOfCards 
{

    private Card deckOfCards[];
    private int currentCardUsed;
    private final int NumberOfCards = 52;

    private int nextCard;

    private Random rand;

    String myString = "All Cards have been dealt.";




    public DeckOfCards()
    {
        deckOfCards = new Card[NumberOfCards];
        currentCardUsed = 0;

        rand = new Random();

        for(int index = 0; index < deckOfCards.length; index ++)
        {
            deckOfCards[index] = new Card();
        }
    }

    public void shuffleCards()
    {
            currentCardUsed = 0;

            for(int newCard = 0; newCard < deckOfCards.length; newCard ++)
            {
                int nextCard = rand.nextInt(NumberOfCards);

                Card temporaryDeck = deckOfCards[newCard];
                deckOfCards[newCard] = deckOfCards[nextCard];
                deckOfCards[nextCard] = temporaryDeck;
            }
    }

    public Card dealCard()
    {
        if(currentCardUsed < deckOfCards.length)
        {
            return deckOfCards[currentCardUsed ++];
        }
        else
        {
            return null;
        }
    }
}

public class DeckTester 
{
    public static void main(String [] args)
    {
        DeckOfCards deck = new DeckOfCards();

        deck.shuffleCards();

        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());

        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());



    }
}

我的一副牌的种类如下

import java.util.*;

public class Card
{
   public final static int ACE   = 1;
   public final static int TWO   = 2;
   public final static int THREE = 3;
   public final static int FOUR  = 4;
   public final static int FIVE  = 5;
   public final static int SIX   = 6;
   public final static int SEVEN = 7;
   public final static int EIGHT = 8;
   public final static int NINE  = 9;
   public final static int TEN   = 10;
   public final static int JACK  = 11;
   public final static int QUEEN = 12;
   public final static int KING  = 13;

   public final static int CLUBS    = 1;
   public final static int DIAMONDS = 2;
   public final static int HEARTS   = 3;
   public final static int SPADES   = 4;

   private final static int NUM_FACES = 13;
   private final static int NUM_SUITS = 4;

   private int face, suit;
   private String faceName, suitName;

   private int myInt1, myInt2;

   Random rand = new Random();

   //-----------------------------------------------------------------
   //  Creates a random card.
   //-----------------------------------------------------------------
   public Card ()
   {
      face = rand.nextInt(4) + 1;
      setFaceName();

      suit = rand.nextInt(13) + 1;
      setSuitName();
   }



   //-----------------------------------------------------------------
   //  Sets the string representation of the face using its stored
   //  numeric value.
   //-----------------------------------------------------------------
   private void setFaceName()
   {
      switch (face)
      {
         case 1:
            faceName = "Ace";
            break;
         case 2:
            faceName = "Two";
            break;
         case 3:
            faceName = "Three";
            break;
         case 4:
            faceName = "Four";
            break;
         case 5:
            faceName = "Five";
            break;
         case 6:
            faceName = "Six";
            break;
         case 7:
            faceName = "Seven";
            break;
         case 8:
            faceName = "Eight";
            break;
         case 9:
            faceName = "Nine";
            break;
         case 10:
            faceName = "Ten";
            break;
         case 11:
            faceName = "Jack";
            break;
         case 12:
            faceName = "Queen";
            break;
         case 13:
            faceName = "King";
            break;
      }
   }

   //-----------------------------------------------------------------
   //  Sets the string representation of the suit using its stored
   //  numeric value.
   //-----------------------------------------------------------------
   private void setSuitName()
   {
      switch (suit)
      {
         case 1:
            suitName = "Clubs";
            break;
         case 2:
            suitName = "Diamonds";
            break;
         case 3:
            suitName = "Hearts";
            break;
         case 4:
            suitName = "Spades";
            break;
      }
   }

   //-----------------------------------------------------------------
   //  Determines if this card is higher than the passed card. The
   //  second parameter determines if aces should be considered high
   //  (beats a King) or low (lowest of all faces).  Uses the suit
   //  if both cards have the same face.
   //-----------------------------------------------------------------
   public boolean isHigherThan (Card card2, boolean aceHigh)
   {
      boolean result = false;

      if (face == card2.getFace())
      {
         if (suit > card2.getSuit())
            result = true;
      }
      else
      {
         if (aceHigh && face == ACE)
            result = true;
         else
            if (face > card2.getFace())
               result = true;
      }

      return result;
   }

   //-----------------------------------------------------------------
   //  Determines if this card is higher than the passed card,
   //  assuming that aces should be considered high.
   //-----------------------------------------------------------------
   public boolean isHigherThan (Card card2)
   {
      return isHigherThan (card2, true);
   }

   //-----------------------------------------------------------------
   //  Returns the face (numeric value) of this card.
   //-----------------------------------------------------------------
   public int getFace ()
   {
      return face;
   }

   //-----------------------------------------------------------------
   //  Returns the suit (numeric value) of this card.
   //-----------------------------------------------------------------
   public int getSuit ()
   {
      return suit;
   }

   //-----------------------------------------------------------------
   //  Returns the face (string value) of this card.
   //-----------------------------------------------------------------
   public String getFaceName ()
   {
      return faceName;
   }

   //-----------------------------------------------------------------
   //  Returns the suit (string value) of this card.
   //-----------------------------------------------------------------
   public String getSuitName ()
   {
      return suitName;
   }

   //-----------------------------------------------------------------
   //  Returns the string representation of this card, including
   //  both face and suit.
   //-----------------------------------------------------------------



   public String toString ()
   {
      return getFaceName() + " of " + getSuitName();
   }
}

import java.util.*;


public class DeckOfCards 
{

    private Card deckOfCards[];
    private int currentCardUsed;
    private final int NumberOfCards = 52;

    private int nextCard;

    private Random rand;

    String myString = "All Cards have been dealt.";




    public DeckOfCards()
    {
        deckOfCards = new Card[NumberOfCards];
        currentCardUsed = 0;

        rand = new Random();

        for(int index = 0; index < deckOfCards.length; index ++)
        {
            deckOfCards[index] = new Card();
        }
    }

    public void shuffleCards()
    {
            currentCardUsed = 0;

            for(int newCard = 0; newCard < deckOfCards.length; newCard ++)
            {
                int nextCard = rand.nextInt(NumberOfCards);

                Card temporaryDeck = deckOfCards[newCard];
                deckOfCards[newCard] = deckOfCards[nextCard];
                deckOfCards[nextCard] = temporaryDeck;
            }
    }

    public Card dealCard()
    {
        if(currentCardUsed < deckOfCards.length)
        {
            return deckOfCards[currentCardUsed ++];
        }
        else
        {
            return null;
        }
    }
}

public class DeckTester 
{
    public static void main(String [] args)
    {
        DeckOfCards deck = new DeckOfCards();

        deck.shuffleCards();

        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());

        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());
        System.out.println(deck.dealCard());



    }
}

输出：

Two of null
Ace of Hearts
Two of null
Four of null
Ace of null
Ace of Spades
Two of Diamonds
Ace of Clubs
Ace of null

对于为什么不是所有卡都有值的任何帮助，我们将不胜感激，

简单错误：

改变

   public Card ()
   {
      face = rand.nextInt(4) + 1;
      setFaceName();

      suit = rand.nextInt(13) + 1;
      setSuitName();
   }

到

其他建议：

• 使用枚举，而不是神奇的数字，你就不会有这样的混乱
• 不要创建随机牌，创建一个完整的牌组并洗牌

---

共有13张脸和4套衣服（您甚至定义了常数）。所以
应该是

face = rand.nextInt(13) + 1;
// ...
suit = rand.nextInt(4) + 1;

或使用先前定义的

卡

常量，如

face = rand.nextInt(Card.NUM_FACES) + 1;
// ...
suit = rand.nextInt(Card.NUM_SUITS) + 1;

---

使用以下代码更新卡构造函数

public Card() {
        Random r = new Random();
        int Low = 1;
        int High = 13;
        face = r.nextInt(High - Low) + Low;
        setFaceName();

        Random r2 = new Random();
        int Low2 = 1;
        int High2 = 4;
        suit = r2.nextInt(High2 - Low2) + Low2;
        setSuitName();
    }

---

这不是问题，但是您可以通过为faces和Suites创建一个类级字符串数组，然后执行类似于

private void setFaceName（）{faceName=faces[face-1]；}

的操作，使代码更干净。我更改了代码段，但现在所有输出都为空，而不仅仅是一些。我修复了它。谢谢大家的帮助