“线程“主”java.util.InputMismatchException中的异常”**

Question

我已经搜索过，但我真的找不到代码有什么问题，请帮忙！

代码可以编译，但这是我想回答问题 3 时遇到的错误：

Exception in thread "main" java.util.InputMismatchException
        at java.util.Scanner.throwFor(Unknown Source)
        at java.util.Scanner.next(Unknown Source)
        at java.util.Scanner.nextDouble(Unknown Source)
        at ForgetfulMachine.main(ForgetfulMachine.java:16)

这是我的代码：

import java.util.Scanner;

public class ForgetfulMachine
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);

        System.out.println( "What city is the capital of Germany?" );
        keyboard.next();

        System.out.println( "What is 6 divided by 2?" );
        keyboard.nextInt();

        System.out.println( "What is your favorite number between 0.0 and 1.0?" );
        keyboard.nextDouble();

        System.out.println( "Is there anything else you would like to tell me?" );
        keyboard.next();
    }
}

Answer 1

Scanner 如果条目的格式对于扫描程序的区域设置不正确，则将引发此异常。特别是，在您的情况下，如果使用了错误的小数分隔符。 . 和 , 都是常见的特定于语言环境的小数分隔符。

要找出您可以使用的默认语言环境的小数分隔符：

System.out.println(
    javax.text.DecimalFormatSymbols.getInstance().getDecimalSeparator()
);

另见：

• Scanner#locale()
• Scanner#useLocale(Locale)
• DecimalFormatSymbols#getInstance(Locale)

Answer 2

您的代码没有问题。在输入数据时尊重类型。当您期望整数等时，请勿输入双精度数。 您可以通过应用防御性编码来解决此类错误，在这种编码中，您仅在符合预期值时才接受来自用户的数据。

public static void main(String[] arg) {
    Scanner keyboard = new Scanner(System.in);

    System.out.println( "What city is the capital of Germany?" );
    keyboard.nextLine();

    System.out.println( "What is 6 divided by 2?" );
    boolean isNotCorrect = true;

    while(isNotCorrect){
        isNotCorrect = true;
        try {
            Integer.valueOf(keyboard.nextLine());       
            isNotCorrect = false;
        } catch (NumberFormatException nfe) {
            System.out.println( "Enter an integer value" );
        }
    }


   System.out.println( "What is your favorite number between 0.0 and 1.0?" );
   isNotCorrect = true;

    while(isNotCorrect){

        try {
             Double.valueOf(keyboard.nextLine());
             isNotCorrect = false;
        } catch (NumberFormatException nfe) {
            System.out.println( "Enter a double value" );
        }
    }

    System.out.println( "Is there anything else you would like to tell me?" );
    keyboard.next();
}