java - 尝试检查猜​​测是否为空时收到异常

Question

这个问题已经有答案了:

Scanner skipping every second line from file [duplicate] (5 个回答)

已关闭 5 年前。

我开发了一款刽子手游戏，已完成 99%。我只有一个小故障，这个小故障是当用户没有输入猜测并按 Enter 时。

我知道我们无法检查字符是否为空，因此我使用 scanner.nextLine().isEmpty() 检查字符串是否为空。现在，如果我不输入任何内容并按 Enter 键，那么它可以正常工作并输出打印行消息。

但是，如果我输入一个字母并按 Enter 键，那么它会转到下一行，并要求我输入一些内容。如果我输入另一个字母，那么它工作正常，如果我什么都不输入并按 Enter 键，那么我会得到一个异常

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0

所以我相信我的问题是 if 语句，我检查字符串是否为空，如果不是，则继续检查字符:

            if (scanner.nextLine().isEmpty()) {
                System.out.println("Your guess seems empty. Please enter in a letter or number");
            } else {

                char input = scanner.nextLine().charAt(0);

                if (input == '-' || Character.isLetter(input) || Character.isDigit(input)) {

                    if (input == '-') {
                        weArePlaying = false;
                        wordCompleted = true;
                    }
....
}

我如何调整它，以便如果为空字符串，则要求用户再次猜测，否则如果不为空，则继续猜测？

下面是更多代码:

public static void main(String[] args) throws FileNotFoundException {

    ArrayList<String> movieList = new ArrayList<>();
    File file = new File("C:\\Users\\mmkp1\\Documents\\listofmovies.txt");
    Scanner fileScanner = new Scanner(file);
    int attempts = 10;
    Scanner scanner = new Scanner(System.in);
    Random random = new Random();
    ArrayList<Character> guessedLetters = new ArrayList<>();

    while (fileScanner.hasNextLine()) {
        String line = fileScanner.nextLine();
        // Reads the whole file
        movieList.add(line);
    }

    boolean weArePlaying = true;
    while (weArePlaying) {
        System.out.println("Welcome to Guess The Movie Game");

        int index = random.nextInt(movieList.size());
        String getMovies = movieList.get(index);
        char[] randomWordToGuess = getMovies.toLowerCase().toCharArray();
        int wordLength = randomWordToGuess.length;
        char[] playerGuess = new char[wordLength];
        boolean wordCompleted = false;

        for (int i = 0; i < playerGuess.length; i++) {
            playerGuess[i] = '_';
        }

        for (int i = 0; i < randomWordToGuess.length; i++) {
            if (randomWordToGuess[i] == ' ') {
                playerGuess[i] = ' ';
            }
        }


        while (!wordCompleted && attempts != 0) {

            printArray(playerGuess);
            System.out.println("Number of attempts left: " + attempts);
            System.out.println("Your previous guesses were:" + guessedLetters);
            System.out.println("Enter a letter or number");

            if (scanner.nextLine().isEmpty()) {
                System.out.println("Your guess seems empty. Please enter in a letter or number");
            } else {

                char input = scanner.nextLine().charAt(0);

                if (input == '-' || Character.isLetter(input) || Character.isDigit(input)) {

                    if (input == '-') {
                        weArePlaying = false;
                        wordCompleted = true;
                    }
....
}

Answer 1

您错误地使用了扫描仪并调用了 nextLine() 两次。

if (scanner.nextLine().isEmpty()) {            // First call.
    System.out.println("empy");
}
else {
    char input = scanner.nextLine().charAt(0); // Second call.
}

假设扫描仪有一条对我们来说很有趣的线。第一次调用将获取它，发现它不为空并将其丢弃。第二次调用不会得到我们感兴趣的行，但会尝试获取(可能是空的)后续行。

尝试访问空字符串的第一个字符会导致您发布的 StringIndexOutOfBoundsException。

您可以借助局部变量轻松修复代码，如下所示:

String line;
char   input;

line = scanner.nextLine();
if (line.isEmpty()) {
    System.out.println("empy");
    return;
}

input = line.charAt(0);
// ...