Write a program to evaluate an arithmetic expression written

Write a program to evaluate an arithmetic expression written in postfixed notation. The arithmetic expression will be input as a String (by the user) and will contain only integer operands. Use the following code sequences to parse (i.e., remove) the integers and the operators from the input string, mathExpression:

import java.util;

String thisToken;

StringTokenizer tokens = new StringTokenizer(mathExpression);

while(tokens.hasMoreTokens())

{ thisToken = tokens.nextToken();

//processing for thisToken goes here

}

My code wont run, I just need some help figuring out what the problem is. Code below.

Solution

import java.util.*;

import javax.swing.*;

import java.util.Stack;
import java.util.StringTokenizer;

public class postfixed2
{

public static void main(String[] args) {
Stack<Double> pfStack = new Stack();
String thisToken;
double n1=2, n2=10, ans;
String mathExpression = JOptionPane.showInputDialog(\"Please enter a post fixed math expression: \");
//StringTokenizer tokens = new StringTokenizer(mathExpression,\"*+/-\");

  
   String digits = mathExpression.replaceAll(\"[0-9]\", \",\");
   //System.out.println(\"digits:::::\"+digits);
   StringTokenizer tokens = new StringTokenizer(digits,\",\");
while(tokens.hasMoreTokens()){
thisToken = tokens.nextToken();
//System.out.println(\"thisadadfsToken::::\"+thisToken);
switch (thisToken){

case \"+\":

ans = n1 + n2;
pfStack.push(ans);
break;

case \"-\":
ans = n1 - n2;
pfStack.push(ans);
break;

case \"*\":
ans = n1 * n2;
pfStack.push(ans);
break;

case \"/\":
ans = n1 / n2;
pfStack.push(ans);
break;

default:
   System.out.println(\"defalut:::\"+thisToken);
pfStack.push(Double.parseDouble(thisToken));
break;

}
}
System.out.println(\"pop::::\"+pfStack.pop());
}   

}
//10 + 2 * 6

Input

10+2*6

output

pop::::12.0