Another method of parsing a command line string

[Randy Helene]

I would like to thank the previous person who helped me with this.
I am writing a java application to parse a command line string such as java ParseEval 3.5 - 7.0 + 8.1. Only + and - operations are allowed. The string can contain spaces. I am at the point where I can find the position of the + or minus signs, but I am having trouble putting the numbers to be evaluated into a statement that can be evaluated.
I tried the method Gautam gave me and it worked. Thank you, because I learned something new. However, I am taking a java class and we haven't gone over push yet. Therefore I need to do this problem using charAt and then putting the numbers between the signs in a substring. I keep getting stuck here, when trying to specify each of the positions in the substring to get the calculation. We also need to allow for the case where the 1st argument is a sign. I'll show you what I have so far. Thank you for your help.
class ParseEval{
public static void main (String args[]) {
if (args.length==0) return;
String s = new String ();
char ch=0;
for (int i = 0; i < args.length; i++)
s=s.concat(args[i]);
for(int j=0; j < s.length();j++){
ch = s.charAt(j);
if ( ch=='+' || ch=='-'){
System.out.println("Ch is " +ch);
System.out.println("position is " +j);
}
}
}
}
Thanks again.

[Peter Allen]

This is an ugly way of doing it, but maybe it'll give you an idea. It works as long as the input is always given in that way.

import java.util.*;
 
class ParseEval
{
    public static void main (String args[])
    {
        if (args.length == 0)
        {
            return;
        }
        String toParse = "";
        double sum = 0;
        for (int i = 0; i < args.length; i++)
        {
            toParse = toParse.concat(args[i]) + " ";
        }
        StringTokenizer st = new StringTokenizer(toParse);
        while(st.hasMoreTokens())
        {
            String s = st.nextToken();
            String s2 = st.nextToken();
            if ( (st.countTokens() > 0) && (s2.equals("+")) )
            {
                sum += Double.parseDouble(s) + Double.parseDouble (st.nextToken());
            }
            if ( (st.countTokens() > 0) && (s2.equals("-")) )
            {
                sum = Double.parseDouble(s) - Double.parseDouble (st.nextToken()) - sum;
            }
        }
        System.out.println (toParse + " equals " + sum);
    }
}

I hope that'll help you.
[ May 03, 2002: Message edited by: Dirk Schreckmann ]

[Doanh Nguyen]

Originally posted by Randy Helene:
However, I am taking a java class and we haven't gone over push yet.

class Java {
static double operand1;
static double operand2;
static String operator = "+";
public static void calc () {
if ((operand1 == 0) && (operand2 == 0)) return;
if (operator.equals("-")) operand1 -= operand2;
else operand1 += operand2;
operator = "+";
operand2 = 0;
}
public static void main (String args[]) {
if (args.length==0) return;
for (int i = 0; i < args.length; i++) {
String s = args[i].trim();
if (s.equals("-")) operator = s;
else if (s.equals("+")) operator = s;
else {
operand2 = Double.parseDouble(args[i]);
calc();
}
}
calc();
System.out.println(operand1);
}
}

[Randy Helene]

Thank you very much. That helped.

[Sayed Ibrahim Hashimi]

If you are using SDK 1.4 then you can use the new Regular Expression package...java.util.regex
This will problably help you a lot if you know about Regular expressions.