SwitchCaseLadder.java

import java.util.Stack;

class ReversePolishNotation {

    public static void main(String[] args) {
        System.out.println(evaluate("5 1 2 + 4 * + 3 -"));
    }

    public static double evaluate(String expr) {
        String[] digitString = expr.split(" ");

        Stack<Float> stack = new Stack<Float>();

        for (String s : digitString) {
            switch (s) {
                case "+": {
                    float numberOne = stack.pop();
                    float numberTwo = stack.pop();
                    stack.push(numberOne + numberTwo);
                    break;
                }
                case "-": {
                    float numberOne = stack.pop();
                    float numberTwo = stack.pop();
                    stack.push(numberTwo - numberOne);
                    break;
                }
                case "*": {
                    float numberOne = stack.pop();
                    float numberTwo = stack.pop();
                    stack.push(numberOne * numberTwo);
                    break;
                }
                case "/": {
                    float numberOne = stack.pop();
                    float numberTwo = stack.pop();
                    stack.push(numberTwo / numberOne);
                    break;
                }
                default: {
                    stack.push(Float.parseFloat(s));
                    break;
                }

            }
        }
        return stack.pop();
    }
}