Go4Expert - Why don't I see any output from my program?

I tried compiling this program several times but did't see any output. Could anyone give me any suggestion on why I'm not seeing any output when I run this code.

Code:

//import java.io.*;

//import java.math.*;

//import java.io.OutputStreamWriter;

import java.io.BufferedInputStream;

//import java.lang.*;

import java.util.*;

import java.util.Scanner;

//import java.io.PrintWriter;

//import java.io.UnsupportedEncodingException;

//import java.util.Locale;





public class StdIn {



private static Scanner scanner = new Scanner(new BufferedInputStream(System.in));





public static boolean isEmpty() 

{ return !scanner.hasNext();}





public static String readString() 

{ return scanner.next();}







public static void main (String args[]){ 





Stack<String> ops = new Stack<String>();



Stack<Double> vals = new Stack<Double>();







while (!StdIn.isEmpty())

{ // Read token, push if operator.

String s = StdIn.readString();

if (s.equals("(")) ;

else if (s.equals("+")) ops.push(s);

else if (s.equals("-")) ops.push(s);

else if (s.equals("*")) ops.push(s);

else if (s.equals("/")) ops.push(s);

else if (s.equals("sqrt")) ops.push(s);

else if (s.equals(")"))



{ // Pop, evaluate, and push result if token is ")".

String op = ops.pop();

double v = vals.pop();

if (op.equals("+")) v = vals.pop() + v;

else if (op.equals("-")) v = vals.pop() - v;

else if (op.equals("*")) v = vals.pop() * v;

else if (op.equals("/")) v = vals.pop() / v;

else if (op.equals("sqrt")) v = Math.sqrt(v);

vals.push(v);

System.out.println(vals.push(v));

} // Token not operator or paren: push double value.

else vals.push(Double.parseDouble(s));

System.out.println(Double.parseDouble(s));



}

System.out.println(vals.pop());        





}





}