Having a problem with a calculator that takes input from command line

Question

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I'm having a problem with this code:

Java

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);
        }
  }
}

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?

Posted 4-Sep-10 8:01am

User 6215579

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Comments

Richard MacCutchan 5-Sep-10 13:04pm

As to your second question you never get the exception because you code falls through if the first character of args[1] is not one of the valid operators.

[no name] 5-Sep-10 13:09pm

But if args[1] was a valid operator, how could I do it then.
Or for exceptions in general how does one get the offending input?

2 solutions

Solution 1

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

Posted 4-Sep-10 9:02am

Uwe Keim

Comments

[no name] 4-Sep-10 15:17pm

I don't have any debuggers and wasn't java discontinued from Visual Studio Express, I could be wrong though and would love a link to it if you have the time.
Also I know the problem, I just don't know what causes it. The calculator works for /,+,- but for some reason it doesn't take in *. The * operator does work however if I enclose it with " ": like 3 "*" 3. Could it be that regular expression is messing with this?

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Richard MacCutchan · Accepted Answer · 2010-09-05T06:49:00

Solution 2

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

Posted 5-Sep-10 6:49am

Richard MacCutchan

Updated 5-Sep-10 6:50am

v2

Comments

[no name] 5-Sep-10 12:51pm

Thanks a lot, I figured out I could do "*" but I couldn't understand why it worked.
So thanks for the answer.

Dalek Dave 5-Sep-10 13:42pm

Good Answer