Evaluate.java

public class Evaluate
{
  public static void main(String[] args)
  {
    ResizingArrayStack<String> ops = new ResizingArrayStack<String>();
    ResizingArrayStack<Double> vals = new ResizingArrayStack<Double>();
    while (!StdIn.isEmpty())
    { // Read char from standard in, push if token.
      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("%"))     ops.push(s);
      else if (s.equals("sqrt"))  ops.push(s);
      else if (s.equals(")"))
      { // If token equals ")", pop two vals, evaluate with op, push result.
        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("%"))    v = vals.pop() % v;
        else if (op.equals("sqrt")) v = Math.sqrt(v);
        vals.push(v);
      } // If token not operator or paren, convert value to double and push.
      else {
        vals.push(Double.parseDouble(s));
      }
    }
    StdOut.println(vals.pop());
  }
}