Java在尝试从Scanner对象收集输入时引发“找不到行”异常

Question

我对Java相当陌生，正在尝试构建一个“十大Java初学者项目”，更具体地说，是一个温度转换器。我的代码引发以下错误：

Exception in thread "main" java.util.NoSuchElementException: No line found
        at java.base/java.util.Scanner.nextLine(Scanner.java:1651)
        at TempConvert.convertToFar(TempConvert.java:78)
        at TempConvert.main(TempConvert.java:15)

我最初使用scanner“*.nextDouble（）”方法获取double，但将其更改为“parseDouble”方法，因为我认为这可能是问题所在。唉，这没有帮助。如果您能帮助解决此问题，我们将不胜感激！

    public static double convertToFar()
    {
        Scanner in = new Scanner(System.in);
        String userEntry;
        double formula, userDouble;
        System.out.print("Enter degrees in Celsius: ");
        userEntry = in.nextLine();
        userDouble = Double.parseDouble(userEntry);
        in.close();
        formula = (userDouble - 32) * (5/9);
        return formula;
    }

Answer 1

我认为，<代码>在。您编写的方法中的nextLine（）最终与用户在关闭输入流之前输入的字符串发生冲突。我创建了一个Scanner对象并将其发送给这些方法，以便它们能够使用相同的对象。我只有在用户输入“E”后程序结束时才关闭它。这对我很有用：

import java.util.*;

public class TempConvert {
    public static void main(String[] args)
    {
    
        double far, cel;
        char userChoice;
        Scanner in = new Scanner(System.in);  // I added this line
        userChoice = displayMenu(in);
        while (userChoice != 'E')
        {
            if (userChoice == 'F')
            {
                far = convertToFar(in);
                System.out.println("Converted: " + far + "\u00B0");
                userChoice = displayMenu(in);
            }
            else if (userChoice == 'C')
            {
                cel = convertToCel(in);
                System.out.println("Converted: " + cel + "\u00B0");
                userChoice = displayMenu(in);
            }
            else
            {
                System.out.println("Invalid Entry");
                userChoice = displayMenu(in);
            }
        }
        in.close();  // closing the input stream when the program ends
    
    
    }

    public static void displayTitle()
    {
        String title = "||---- TEMPERATURE CONVERTER ----||";
        String one = "-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-";
        String two = "||       ** Auth: Arranic        ||";
        String three = "||                               ||";

        System.out.println(one + "\n" + three + "\n" + title + "\n" + three     + "\n" + two + "\n" + three + "\n" + one);
    }

    public static char displayMenu(Scanner input)
    {
        ClearScreen();
        displayTitle();

        System.out.println("\n");

        String choiceString;
        char choice;
    
        System.out.println("F - FARENHEIGHT      C - CELSIUS      E - EXIT");
        System.out.print("CONVERT TO: ");
        choiceString = input.nextLine();
        // input.close()   --> removed this line
        choice = Character.toUpperCase(choiceString.charAt(0));

        return choice;
    }

    public static void ClearScreen()
    {
        System.out.print("\033[H\033[2J");
        System.out.flush();
    }

    public static double convertToCel(Scanner in)
    {
        String userEntry;
        double formula, userDouble;
        System.out.print("Enter degrees in Fahrenheit: ");
        userEntry = in.nextLine();
        // in.close()   --> removed this line
        userDouble = Double.parseDouble(userEntry);
        formula = (userDouble - 32) * (5.0/9);
        return formula;
    }

    public static double convertToFar(Scanner in)
    {
        String userEntry;
        double userDouble, formula;
        System.out.print("Enter degrees in Celsius: ");
        userEntry = in.nextLine();
        // in.close()   --> removed this line
        userDouble = Double.parseDouble(userEntry);
        formula = (userDouble * (9.0/5)) + 32;
        return formula;
    }
}

顺便说一句，你的计算并不精确。你应该记住整数/整数=整数。也就是说，写5/9或9/5是不准确的，因为结果是一个整数类型的数字，而不是我假设你想得到的双类型的数字。（5/9 = 0, 9/5 = 1)所以你应该在计算中添加5.0或9.0，这样Java就会明白你想得到双类型的结果（双/int=双）。还有一件事，你的计算放错了地方（华氏度到摄氏度给了我相反的结果，反之亦然），所以我把它们换了起来；）。