遇到从命令行输入的计算器有问题 [英] Having a problem with a calculator that takes input from command line

问题描述

我对此代码有疑问:

I''m having a problem with this code:

public class Calculator
{
    public static void main(String[] args)
    {
        try
        {
            int result = 0;
            try
            {
                switch (args[1].charAt(0))
                {
                  case '+': result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
                            break;
                  case '-': result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
                            break;
                  case '*': result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
                            break;
                  case '/': result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
                            break;
                }
                System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = " + result);
            }
            catch(NumberFormatException ex)
            {
                System.out.println(ex.getMessage());
                System.exit(0);
            }
        }
        catch(Exception ex)
        {
            System.out.println("You have to enter it in as: Number1 operator Number2");
            System.exit(0);
        }
  }
}

问题是，当我在命令行中输入3 + 3时，它可以工作，但是如果我写3 * 3，则arg数组会打印出Calculator.class，为什么会发生这种情况?

The problem is that when I toss in 3 + 3 in the command line it works but if I write 3 * 3 the arg array prints out the Calculator.class, why does this happen?

Also Is there a way in NumberFormatException catch to print out the offending input?

推荐答案

问题还在于*字符由外壳程序解释，并由列表替换进行调用的目录中的文件和目录.您需要使用另一个字符来表示乘号或在(双引号)字符内提交*，这样:

The problem is that the * character is interpreted by the shell and is replaced by a list of the files and directories in the directory that the call is made from. You need to use another character to represent multiply or submit the * within " (double quote) characters thus:

java Calculator 3 "*" 3
// or using x character
java Calculator 3 x 3

如何启动调试器，设置一些断点等?

如果还没有免费的工具，请使用免费的Visual Studio Express Edition.

干杯
Uwe

How about firing up a debugger, setting some breakpoints, and the like?

Just use the free Visual Studio Express Edition, if you have no such tool yet.

Cheers
Uwe

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