Reverse Polish Notation Java - stack

Question

I want to make Reverse Polish Notation algorithm, but my code isn't working. Can anyone explain me why ?
In my code, I would like to take the characters, until "/+-*"tokens . If this tokens was next , make operation , that contains in case .
import java.util.Stack;
import java.util.StringTokenizer;
import javax.swing.JOptionPane;
public class ONP {
public static void main(String[] args) {
Stack<Double> stack = new Stack<Double>();
double number1;
double number2;
String x = JOptionPane.showInputDialog("Tokens");
StringTokenizer str = new StringTokenizer(x);
while (str.hasMoreElements()) {
str.nextElement();
stack.push((Double) str.nextElement());
for (int i = 0; i < x.length(); i++) {
switch (x.charAt(i)) {
case '+':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 + number2);
break;
case '-':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 - number2);
break;
case '/':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 / number2);
break;
case '*':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 * number2);
break;
}
}
System.out.println(stack.pop());
}
}
}
I would like to write it without StringBuilder or sth like that.
Input:
2 2 + 2 / 2 /
Output :
(2+2) / 2 / 2

Answer 1

try this
String s1;
while (str.hasMoreElements())
{
s1 = str.nextElement();
if(s1.equals("+") || s1.equals("-") || s1.equals("*") || s1.equals("/"))
{
switch (s1)
{
case '+':
number1 = stack.pop();
number2 = stack.pop();
System.out.print(number1 + " + " + number2);
break;
case '-':
number1 = stack.pop();
number2 = stack.pop();
System.out.print(number1 +" - "+ number2);
break;
case '/':
number1 = stack.pop();
number2 = stack.pop();
System.out.print(number1 +" / "+ number2);
break;
case '*':
number1 = stack.pop();
number2 = stack.pop();
System.out.print(number1 +" * "+ number2);
break;
}
}
else
{
stack.push(s1);
}
}
instead of
while (str.hasMoreElements()) {
str.nextElement();
stack.push((Double) str.nextElement());
for (int i = 0; i < x.length(); i++) {
switch (x.charAt(i)) {
case '+':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 + number2);
break;
case '-':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 - number2);
break;
case '/':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 / number2);
break;
case '*':
number1 = stack.pop();
number2 = stack.pop();
System.out.println(number1 * number2);
break;
}
}
System.out.println(stack.pop());
}