Write a program to evaluate an arithmetic expression written in postfixed notati

Question

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.

Explanation / Answer

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

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