扫描仪NoSuchElementException

时间:2013-03-15 22:55:07

标签: java exception java.util.scanner

我的Java分配有问题。我得到了一个意想不到的例外,特别是:

  

java.util.NoSuchElementException:找不到行

我正在使用Scanner(System.in)并且该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int,则第一部分通过,然后double部分立即进入此异常。如果我输入的值不正确int,则会开始循环异常。

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;
    }
}

2 个答案:

答案 0 :(得分:18)

您关闭了多个Scanner,这会关闭基础InputStream,因此另一个Scanner无法再从同一InputStream和{{{ 1}}结果。

对于控制台应用,请使用一个NoSuchElementException来阅读Scanner

答案 1 :(得分:3)

由于您在捕获异常的所有三个地方打印出相同的消息,因此很难确切地说出发生了什么:

  • 使用printStackTrace()查找异常发生的位置

  • 不要那样抓住Exception。捕获您期望的异常以及您的代码旨在处理的异常。如果您抓住Exception,您最终可能会捕获各种意外例外(NPE,文件结尾等)......并且错误地将其报告为“格式无效“。