扫描仪 NoSuchElementException [英] Scanner NoSuchElementException

问题描述

我的 Java 作业有问题.我遇到了一个意外的异常，特别是:

I'm having a problem with my Java assignment. I'm getting an unexpected exception, specifically:

java.util.NoSuchElementException:找不到行

java.util.NoSuchElementException: No line found

我正在使用 Scanner(System.in) 并且程序不断读取任何内容并重复无效格式"异常文本.如果我输入正确值的 int，第一部分通过，然后 double 部分立即进入此异常.如果我输入了一个不正确的值 int，那么它就会开始循环异常.

I am using Scanner(System.in) and the program is continually reading nothing and repeating the "invalid format" exception text. If I enter a correctly valued int, the first part passes and then the double part immediately goes into this exception. If I enter an incorrectly valued int, then it starts looping the exception.

这是我的代码:

import java.util.Scanner;

public class Program_4 {

    public static void main(String[] args) {
        getValidInt("Enter an integer from 5 to 50",5,50);
        getValidDouble("Enter a double from 5.0 to 50.0",5.0,50.0);
        getValidString("Enter a string with length from 5 to 8 characters",5,8);
    }


    public static int getInt(String prompt)
    {
       Scanner sc = new Scanner(System.in);
       int i = 0;
       boolean isValid;
       do
       {
          try
          {
             System.out.print(prompt + ": ");
             i = Integer.parseInt(sc.nextLine());
             isValid = true;
          } 
          catch (Exception e)
          {
              System.out.println(e);
              System.out.print("Invalid Format: ");
              isValid = false;
          }
       }
       while (isValid == false);
       sc.close();
       return i;
    }

    public static int getValidInt(String prompt, int min, int max)
    {
        int i = 0;
        boolean isValid = false;
        do
        {
            i = getInt(prompt);
            if(i < min) System.out.println("Value must be >= " + min);
            else if(i > max) System.out.println("Value must be <= " + max);
            else isValid = true;
        } while (isValid == false);

        return i;
    }

    public static double getDouble(String prompt)
    {
       Scanner sc = new Scanner(System.in);
       double i = 0.0;
       boolean isValid;
       do
       {
          try
          {
             System.out.print(prompt + ": ");
             i = Double.parseDouble(sc.nextLine());
             isValid = true;
          } 
          catch (Exception e)
          {
              System.out.println(e);
              System.out.println("Invalid Format: ");
              isValid = false;
          }
       } while (isValid == false);
       sc.close();
       return i;
    }

    public static double getValidDouble(String prompt, double min, double max)
    {
        int i = 0;   
        boolean isValid = false;
        do
        {
            i = getInt(prompt);
            if(i < min) System.out.println("Value must be >= " + min);
            else if(i > max) System.out.println("Value must be <= " + max);
            else isValid = true;
        } while (isValid == false);

        return i;
    }

    public static String getString(String prompt)
    {
       Scanner sc = new Scanner(System.in);
       String i="";
       boolean isValid;
       do
       {
          try
          {
             System.out.print(prompt + ": ");
             i = sc.nextLine();
             isValid = true;
          } 
          catch (Exception e)
          {
              System.out.print("Invalid Format: ");
              isValid = false;
          }
       } while (isValid == false);
       sc.close();
       return i;
    }

    public static String getValidString(String prompt, int min, int max)
    {
        String i;
        boolean isValid = false;

        do
        {
            i = getString(prompt);
            if(i.length() < min) System.out.println("String must be more than "       + min + " characters.");
            else if(i.length() > max) System.out.println("String must be more     than " + max + " characters.");
            else isValid = true;
        } while (isValid == false);

        return i;
    }
}

推荐答案

您关闭了多个 Scanner，这会关闭底层 InputStream，因此另一个 Scanner 无法再从相同的 InputStream 和 NoSuchElementException 结果中读取.

You have more than one Scanner that you close, which closes the underlying InputStream, therefore another Scanner can no longer read from the same InputStream and a NoSuchElementException results.

对于控制台应用程序，使用单个 Scanner 来读取 System.in.

For console apps, use a single Scanner to read from System.in.

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