Dijkstraの二重スタック演算式の求め方

package First;

import java.util.Scanner;
import java.util.Stack;
import java.util.regex.Pattern;

public class Evaluate {
    public static void main(String[] args) {
        //    
        Stack opsStack = new Stack<>();
        //    
        Stack valsStack = new Stack<>();
        //              
        String ops = "+-*/sqrt";
        Scanner input = new Scanner(System.in);
        //     
        String exp = input.nextLine();
        for(int i = 0;i < exp.length();i++){
            String s = exp.charAt(i) + "";
            if(s.matches("[\\(\\s]")) continue;
            //      
            if (ops.contains(s)){
                opsStack.push(s);
            } else if(s.equals(")")){ //     ”）“，         ，           
                String op = opsStack.pop();
                double v = valsStack.pop();
                if(op.equals("+")) v = valsStack.pop() + v;
                else if(op.equals("-")) v = valsStack.pop() - v;
                else if(op.equals("*")) v = valsStack.pop() * v;
                else if(op.equals("/")) v = valsStack.pop() / v;
                else if(op.equals("sqrt")) v = Math.sqrt(v);
                valsStack.push(v);
            }
            //              ，    double    
            else valsStack.push(Double.parseDouble(s));
        }
        System.out.println(valsStack.pop());
    }
}