Question

我是编程和Java的新手。我遇到的问题是我的程序只识别大写字母，如果用户输入是非字母字符则显示错误信息。我被指示使用布尔和字符串来解决这个问题。谢谢！

Scanner in = new Scanner(System.in);
System.out.println("Enter a single letter, and I will tell you what the corresponding digit is on the telephone:");
String letter = in.nextLine();
String upperCase = letter.toUpperCase();
boolean letter = letter.hasUpperCase();


if (letter.equals("A") || letter.equals("B") || letter.equals("C")){
 System.out.println("The digit 2 corresponds to the letter " + letter + " on the telephone.");
}
else if{
  System.out.println("Please enter a letter.")
}

Answer 1

如果你只想检查大写字母，那么一种方法是检查每个字符的ASCII值，看它是否在65到90之间。如果字符串中的所有字符符合这个标准，那么你有一个字符串仅包含AZ。如果没有，您可以根据需要显示错误消息。请根据您的代码查看以下示例。

    Scanner in = new Scanner(System.in);
    System.out.println("Your message here");
    String userInput = in.nextLine();
    in.close();
    // Here you don't know what they entered
    // but looking at your code, you want 
    // only ONE uppercase character

    // validate the input
    boolean validInput = false;

    if (userInput.length() == 1) {
        char letter = userInput.charAt(0);
        if (letter >= 65 && letter <= 90) {
            validInput = true;
        }
    }

    // handle accordingly
    if (validInput) {
        // your logic here
    } else {
        System.out.println("Your error message");
    }

编辑 - 如何检查字符是数字还是符号

...

    // Here you don't know what they entered

    // the validation / execution changes based on your needs
    // suggestion: define other methods

    if (userInput.length() == 1) {
        char c = userInput.charAt(0);

        // what kind of character is it?
        if (isUppercaseLetter(c)) {
            // do something with the uppercase letter
        } else if (isDigit(c)) {
            // do something with the digit
        } else if (isSymbol(c)) {
            // do something with the symbol
        } else {
            // whatever else it might be, this could be an error message
        }
    }

...

// methods here
private boolean isUppercaseLetter(char c) {
    return (c >= 'A' && c <= 'Z'); // ascii codes 65 to 90
}

private boolean isDigit(char c) {
    return (c >= '0' && c <= '9'); // ascii codes 30 to 39
}

private boolean isSymbol(char c) {
    return (c >= '!' && c <= '/'); // 21 to 47, modify based on acceptable symbols
}

Answer 2

我不确定你的要求。但是我修改了你的代码，所以它可以根据我看待它的方式运行。

    Scanner in = new Scanner(System.in);
    System.out.println("Enter a single letter, and I will tell you what the corresponding digit is on the telephone:");
    String letter = in.nextLine();
    boolean hasUpper = false;


    if (letter.equals("A") || letter.equals("B") || letter.equals("C")){
        hasUpper = true;
        System.out.println("The digit 2 corresponds to the letter " + letter + " on the telephone.");
    }
    else if(letter.equals("a") || letter.equals("b") || letter.equals("c")){
        System.out.println("Error! The letter has to be uppercase.");
    }
    else{
         System.out.println("Please enter a letter.");
    }

Java：如何使用boolean和string编写程序以仅识别大写字母

2 个答案: