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;
}
}
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“。