Use RPN(Reverse Polish Notation) to implement calculator

RPN(Reverse Polish Notation): Operators follow their operands, in contrast to PN(Polish Notation).

public class ReversePolishNotation {
    public static void main(String[] args) {
//        (3+4)*5-6 --> 3 4 + 5 * 6 -
        String suffixNotation = "3 4 + 5 * 6 -";

//        get string list
        List<String> rpnList = getListString(suffixNotation);

//        test
        int result = calculate(rpnList);
        System.out.println(result);

    }

    public static List<String> getListString(String suffixNotaion) {
        String[] split = suffixNotaion.split(" ");
        List<String> list = new ArrayList<String>();
        for (String element : split) {
            list.add(element);
        }
        return list;
    }

    //    RPN: from left to right
    public static int calculate(List<String> list) {
        //only need one stack
        Stack<String> strings = new Stack<>();
        for (String s : list) {
            //regex
            if (s.matches("\\d+")) {//multi-number
                //push in numbers
                strings.push(s);
            } else { //when it comes to operator
                //calculate 2 numbers, then push in the result
                int num2 = Integer.parseInt(strings.pop());
                int num1 = Integer.parseInt(strings.pop());
                int result = 0;
                switch (s) {
                    case "+":
                        result = num1 + num2;
                        break;
                    case "-":
                        result = num1 - num2;
                        break;
                    case "*":
                        result = num1 * num2;
                        break;
                    case "%":
                        result = num1 / num2;
                        break;
                    default:
                        throw new RuntimeException("There's something wrong with the operator.");
                }
                strings.push(String.valueOf(result));
            }
        }
        return Integer.parseInt(strings.pop());
    }
}