Question

我的甲板类遇到问题，我的代码创建了一个有限的牌组，并将从数组中返回一个值，然后将其设为null。它还会检查它是否为空，因为getCard（）被多次调用。这确保没有重复的卡。问题是，当我运行我的代码时，它打印出空行，这必须意味着它返回null，这是我的理解发生的。

public class Deck {

  public int randomNumber;
  private String card;
  private String [] deck;
  public Deck()
  {
    deck = new String [] {"Ace Of Hearts" , "2 Of Hearts" , "3 Of Hearts" , "4 Of Hearts" , "5 Of Hearts" , "6 Of Hearts" , "7 Of Hearts" , 
  "8 Of Hearts" , "9 Of Hearts" , "10 Of Hearts" , "Jack Of Hearts" , "Queen Of Hearts" , "King Of Hearts" ,
  "Ace Of Diamonds" , "2 Of Diamonds" , "3 Of Diamonds" , "4 Of Diamonds" , "5 Of Diamonds" , "6 Of Diamonds" ,
  "7 Of Diamonds" , "8 Of Diamonds" , "9 Of Diamonds" , "10 Of Diamonds" , "Jack Of Diamonds" , "Queen Of Diamonds" ,
  "King Of Diamonds" , "Ace Of Clovers" , "2 Of Clovers" , "3 Of Clovers" , "4 Of Clovers" , "5 Of Clovers" ,
  "6 Of Clovers" , "7 Of Clovers" , "8 Of Clovers" , "9 Of Clovers" , "10 Of Clovers" , "Jack Of Clovers" ,
  "Queen Of Clovers" , "King Of Clovers" , "Ace Of Spades" , "2 Of Spades" , "3 Of Spades" , "4 Of Spades" , "5 Of Spades" ,
  "6 Of Spades" , "7 Of Spades" , "8 Of Spades" , "9 Of Spades" , "10 Of Spades" , "Jack Of Spades" ,
  "Queen Of Spades" , "King Of Spades"};
  }

  public String getCard ()
  {
    randomNumber = (int) (Math.random() * 51) + 1;
    String tempCard;
    if (deck[randomNumber] != null)
    {
      tempCard = deck[randomNumber];
      deck[randomNumber] = ("");
      return (tempCard); 
    }
else
{
  while (deck[randomNumber] == null)
  {
    randomNumber = (int) (Math.random() * 51) + 1;
  }
  tempCard = deck[randomNumber];
  deck [randomNumber] = ("");
  return (tempCard);
  }
  }
}

这是一个运行我的甲板课程的测试程序：

import hsa.Console;

public class DeckTest {
static Console c;

  public static void main(String[] args) {

//The Console 
c = new Console();

Deck Card = new Deck();

c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
c.println(Card.getCard());
  }
 }

Answer 1

这项测试是徒劳的：

deck[randomNumber] != null

因为你所有的牌组元素都不是空的，你用＆＃34;＆＃34;替换抽出的牌，这是空字符串，但不是空的。

使用

 deck [randomNumber] = null;

还应该改进循环。

private Random rand = new Random();
public String getCard () {
    String tempCard = null;
    do {
        int r = rand.nextInt( deck.length );
        tempCard = deck[r];
        deck[r] = null;
    } while( tempCard == null );
    return tempCard; 
}

应该添加一个测试，以便不要试图绘制比甲板上更多的东西。

Answer 2

使用您的代码可以改进一些事项。

要解决您的问题：""与null不同。前者是非空的空字符串。后者是指向什么都没有的指针。您将需要使用后者使您的空检查str == null按预期工作。

数组是0索引的。出于某种原因，在你的随机数字中你加1，使得心灵之王成为一张永远无法选择的牌。你想要的是确保你乘以元素数量的大小。这将从[0, size)创建一个均匀分布的数字，并使用强制转换为整数将为您提供正确的数字。

我还建议使用while循环查看do-while循环而不是if语句。这将大大清理您的代码。

Java - 创建卡片组类

2 个答案: