在 java 中，如何处理有关 Windows 命令行参数的异常？

Question

我浏览了一堆其他问题和在线，但找不到任何具体回答这个问题的内容。我正在尝试根据 Windows 命令行参数处理和确定有效输入。作为示例，我只是想尽可能简单地查看输入的数字是否为正数。最大的问题，也是让我无法找到具体答案的原因，是我真的在尝试使用递归让它一直询问直到输入有效输入，而不是仅仅终止程序。

Algorithm:
If there is an argument provided and it's a positive integer
    Display value
Otherwise
    Until the argument is a positive number
        Prompt for a positive integer
    Display value

我与代码搏斗并最终让它工作，但它看起来确实效率低下，重复并且被黑客攻击在一起。起初，我在捕获的异常中有 while 循环，但这允许其他东西从命令行中溜走。我怎样才能使它尽可能高效并防止任何逻辑错误或异常？解决这个问题时，我的算法应该采用什么方法？这是我的代码：

import java.util.Scanner;


public class Test
{
    public static void main( String[] args )
    {
        String arg;
        Scanner user_input = new Scanner(System.in);
        int i = 0;

        try {
            arg = args[0];
            i = Integer.parseInt(arg);
        } catch( ArrayIndexOutOfBoundsException e ) {
            arg = "";
        } catch( NumberFormatException e2 ) {
            arg = "";
        }

        while( i <= 0 )
        {
            System.out.print("Please type in a positive whole number.  ");
            arg = user_input.next();

            try {
                i = Integer.parseInt(arg);
            } catch( NumberFormatException e2 ) {
                System.out.print("That's a letter! ");
                continue;
            }

            if( i <= 0 )
            {
                System.out.print("That's a negative. ");
            }
        }


        System.out.println("Input is " + i);
    }
}

Answer 1

我修改了你的代码，让它按照你想要的方式运行。试试这个：

public static void main( String[] args ) {
    String arg;
    Scanner user_input = new Scanner(System.in);
    int numTries = 0, value = 0;

    try {
        numTries = Integer.parseInt(args[0]);      // get max number of tries
    } catch (ArrayIndexOutOfBoundsException e) {
        arg = "";
    } catch (NumberFormatException e2) {
        arg = "";
    }

    // try 'numTries' times to read a valid number input
    for (int i=numTries; i > 0; --i) {
        System.out.print("Please type in a positive whole number: ");
        arg = user_input.next();

        try {
            value = Integer.parseInt(arg);
        } catch(NumberFormatException e2) {
            System.out.println("That's a letter! ");
            continue;
        }

        if (value <= 0) {
            System.out.println("That's a negative. ");
        }
        break;                                     // exit loop if number input found
    }

    System.out.println("Input is " + value);
}

此代码已在 IntelliJ 上测试，运行没有问题。

Answer 2

试试这个：

代码很长，这是因为需要两个单独的try块；一个用于命令行参数，另一个用于通过扫描器提供的参数...

我必须创建自己的自定义异常，"NegativeNumberException"...

        import java.util.Scanner;

    public class NegativeNumberException extends Exception{

        NegativeNumberException(){
            System.out.println(exceptionMessage);
        }

        String exceptionMessage = "Number must be positive";
        static int num;

        public static void main(String[] args) throws NegativeNumberException{

            try
            {
            if(Integer.parseInt(args[0])<0){
                throw new NegativeNumberException();
            }
            else{
                 int num = Integer.parseInt(args[0]);
                 System.out.println("Your number is: " + num);

            }
            }
            catch(NumberFormatException ex){
                System.out.println("That's not even a number.");

            }
            catch(NegativeNumberException ex){
                ex.getMessage();
            }



            while(num==0){
            try{
                System.out.println("Enter a positive number:");
                Scanner input = new Scanner(System.in);
                int num1 = input.nextInt();
                if(num1<0){
                    throw new NegativeNumberException();
                }
                num = num1;
                break;
            }catch(Exception ex){
                System.out.println("Positive number only, try again...");
                }
            }//End While

            System.out.println("Your number is:" + num);
            }

    }

输入：（命令行）：哈哈

输出

       (Console):That's not even a number
                  Enter a positive int

       (Console input via Scanner): -4

       (Console):Number must be positive
                 Positive number only, try again...
                 Enter a positive number:

       (Console input via Scanner): 3


       (Console):Your number is: 3

在 java 中，如何处理有关 Windows 命令行参数的异常？

In java, how can I handle exceptions regarding Windows command line arguments?

java

command-line

user-input

exception