String arguments

[Marie Jeanne Thibault]

I'm really stuck. I only want this program accept integer input. Any other input like a char I want it to display a message that it is the wrong type of input and display the input in question. Here is what I've got so far. Any help would be appreciated.
Thanks,
Marie
//ExceptDemo1b.java
public class ExceptDemo1b
{
//Main Method with three arguments
//args[0]: operator
//args[1]: operand1
//args[2]: operand2
public static void main(String[] args)
{
//Declare and initialize variables
int result = 0;
int operand1 = 0;
int operand2 = 0;
if (args.length != 3)
{
System.out.println("Usage: java Calculator operator operand1 operand2");
System.exit(0);
}
if(((operand1 >= 0) || (operand1 < 0)) && ((operand2 >= 0) || (operand2 < 0)))
{
operand1 = Integer.parseInt(args[1]);
operand2 = Integer.parseInt(args[2]);
switch (args[0].charAt(0))
{
case '+': result = Integer.parseInt(args[1]) +
Integer.parseInt(args[2]);
break;
case '-': result = Integer.parseInt(args[1]) -
Integer.parseInt(args[2]);
break;

case '*': result = Integer.parseInt(args[1]) *
Integer.parseInt(args[2]);
break;
case '/': result = Integer.parseInt(args[1]) /
Integer.parseInt(args[2]);
}
//Display the result
System.out.println(args[1]+ ' ' +args[0]+ ' ' +args[2]+ "=" +result);
}
else
{
System.out.println("Wrong input ");
System.exit(0);
}

}
}

[Michael Morris]

Hi Marie,
Welcome to JavaRanch. Well, this stuff is always kinda tricky. First, you should probably try a divide and conquer strategy on the usage. Set up some constants for the usage strings and exit codes (by Unix standards you shouldn't exit 0 on an exceptional event) and create some private methods to actually print the message and exit for you when something bad happens. We Java programmes use a little trick to verify numeric input buy wrapping the parse methods in a try/catch for NumberFormatException. Take a look at this and see if it makes sense to you, if not ask some more questions:

public class ExceptDemo1b
{
    private static final String USAGE = "Usage: java Calculator operator operand1 operand2";
    private static final String INPUT = "Invalid input";
    private static final int BAD_USAGE = 1;
    private static final int BAD_INPUT = 2;
    public static void main(String[] args)
    {
        int result = 0;
        int operand1 = 0;
        int operand2 = 0;
        if (args.length != 3)
        {
            printUsageAndExit();
        }
        try
        {
            operand1 = Integer.parseInt(args[1]);
            operand2 = Integer.parseInt(args[2]);
        }
        catch (NumberFormatException nfe)
        {
            printInvalidAndExit();
        }

        if(((operand1 >= 0) || (operand1 < 0)) && ((operand2 >= 0) || (operand2 < 0)))
        {
            if (args[0].equals("+"))
            {
                result = operand1 + operand2;
            }
            else if (args[0].equals("-"))
            {
                result = operand1 - operand2;
            }
            else if (args[0].equals("*"))
            {
                result = operand1 * operand2;
            }
            else if (args[0].equals("/"))
            {
                result = operand1 / operand2;
            }
            else
            {
                printInvalidAndExit();
            }
        }
        else
        {
            printStatusAndExit("Input out of range", 3);
        }
    }

    private static void printInvalidAndExit()
    {
        printStatusAndExit(INPUT, BAD_INPUT);
    }
    private static void printUsageAndExit()
    {
        printStatusAndExit(USAGE, BAD_USAGE);
    }
    private static void printStatusAndExit(String usage, int exitCode)
    {
        System.out.println(usage);
        System.exit(exitCode);
    }
}

[Jim Yingst]

 if(((operand1 >= 0) || (operand1 < 0)) && ((operand2 >= 0) || (operand2 < 0)))

I'm curious, what do you want this line to do? Whatever it is, I suspect that you should study this expression carefully - it probably doesn't do what you think it does.