为什么我的 java while 循环继续以真实状态打印？答案

【问题标题】：Why is my java while loop continue printing with true status?为什么我的 java while 循环继续以真实状态打印？
【发布时间】：2020-03-29 08:16:56
【问题描述】：

下面我有一个数组，我正在检查用户输入，猜测我钱包中的卡类型？如果为真，则退出 while 循环，否则再次询问用户，直到与我的数组中的相同卡类型匹配。我的问题是当用户猜测正确时，我仍然收到“卡类型不正确重试消息”。有没有办法缩短我的代码或更好地纠正它？

public static void main(String[] args) {
    String correctGuess = validateGuessedCardType();
    System.out.println(correctGuess);
}

private static final String[] cardsTypesInWallet = {
    "DBS",
    "POSB",
    "AMEX",
    "Standard Charted"
};

private static String validateGuessedCardType() {
    boolean correctGuess = false;

    String guessedCard = "";
    while (!correctGuess) {
        in = new Scanner(System.in);
        System.out.println("Guess a card in my wallet");
        guessedCard = in.nextLine();

        for (int i = 0; i < cardsTypesInWallet.length; i++) {
            if (cardsTypesInWallet[i].equals(guessedCard)) {
                correctGuess = true;
            }
        }
        System.out.println("Card Type is incorrect");
        System.out.println("try again");
    }
    return guessedCard;
}

【问题讨论】：

java 中的while 循环评估块中的所有代码，然后检查条件。如果您想在某些代码之后立即中断循环，请添加if (!correctGuess) {break;}

标签： java arrays while-loop boolean

【解决方案1】：

因为循环没有终止，所以一直持续到结束。如果匹配，您可以从for 循环返回值

private static String validateGuessedCardType() {

    String guessedCard = "";
    while (true) {
        in = new Scanner(System.in);
        System.out.println("Guess a card in my wallet");
        guessedCard = in.nextLine();

        for (int i = 0; i < cardsTypesInWallet.length; i++) {
            if (cardsTypesInWallet[i].equals(guessedCard)) {
                return guessedCard;
            }
        }

        System.out.println("Card Type is incorrect");
        System.out.println("try again");
    }
}

【讨论】：

【解决方案2】：

因为您没有将那些 System.out 行放在适当的 if 子句中。

请注意，您正在运行 for 循环，但实际上并不确定循环需要运行的迭代次数 - 因为定义是“继续遍历所有循环，除非其中一个是正确的。如果一个是正确的，请停止”。

这将是进行这两个修复的结果代码。

还请记住，不建议使用中断操作数，因为它违反结构化编程范式推理 - 它会“破坏”结构。因此，即使它可以用来改进你的代码，我建议你改为遵循这个建议。

private static String validateGuessedCardType() {
        boolean correctGuess = false;

        String guessedCard = "";
        while (!correctGuess) {
            in = new Scanner(System.in);
            System.out.println("Guess a card in my wallet");
            guessedCard = in.nextLine();

            int i=0;
            while(i < cardsTypesInWallet.length && !correctGuess) {
                if (cardsTypesInWallet[i].equals(guessedCard)) {
                    correctGuess = true;
                }
                else i++;
            }
            if(!correctGuess){
                System.out.println("Card Type is incorrect"); System.out.println("try again");
            }
        }
        return guessedCard;
    }

【讨论】：

【解决方案3】：

试试这个

    public class Test1 {
    static Scanner in = new Scanner(System.in);
    public static void main(String[] args) {
        String correctGuess = validateGuessedCardType();
        System.out.println(correctGuess);
    }

    private static final String[] cardsTypesInWallet = {
            "DBS",
            "POSB",
            "AMEX",
            "Standard Charted"
    };

    private static String validateGuessedCardType() {
        boolean correctGuess = false;
        String guessedCard = "";
        while (!correctGuess) {

            System.out.println("Guess a card in my wallet");
            guessedCard = in.nextLine();

            for (int i = 0; i < cardsTypesInWallet.length; i++) {
                if (cardsTypesInWallet[i].equals(guessedCard)) {
                    correctGuess = true;
                }
            }
            if(correctGuess) {
                System.out.println("Card Type is correct");
            } else {
                System.out.println("Card Type is incorrect");
                System.out.println("try again");
            }
        }
        return guessedCard;
    }
}

【讨论】：

【解决方案4】：

    private static String validateGuessedCardType() {
        boolean correctGuess = false;

        String guessedCard = "";
        outer:
        while (!correctGuess) {
            in = new Scanner(System.in);
            System.out.println("Guess a card in my wallet");
            guessedCard = in.nextLine();

            for (int i = 0; i < cardsTypesInWallet.length; i++) {
                if (cardsTypesInWallet[i].equals(guessedCard)) {
                    break outer;
                }
            }
            System.out.println("Card Type is incorrect");
            System.out.println("try again");
        }
        return guessedCard;
    }


OR

    private static final List<String> cardsTypesInWallet = Arrays.asList{
      "DBS",
      "POSB",
      "AMEX",
      "Standard Charted"
  };

    private static String validateGuessedCardType() {
      boolean correctGuess = false;

      String guessedCard = "";
      while (!correctGuess) {
          in = new Scanner(System.in);
          System.out.println("Guess a card in my wallet");
          guessedCard = in.nextLine();

          if (cardsTypesInWallet.contains(guessedCard){
  correctGuess = true;
 }
    else {
   System.out.println("Card Type is incorrect");
          System.out.println("try again");
}

      }
      return guessedCard;
  }

【讨论】：