Evaluate.java in pgm

Evaluate.java

public class Evaluate

{

 public static void main(String[] args)

 {

     Stack ops  = new Stack();

      Stack vals = new Stack();

       while (!StdIn.isEmpty())

        {

            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(")")) {

                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);

            }

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

        }

        StdOut.println(vals.pop());

    }

}