逆波兰表达式利用栈实现（Java)

参考代码:

import java.util.Scanner;
import java.util.Stack;

//逆波兰表达式
public class Main {
    public static void main(String[] args) {
        //输入逆波兰表达式字符串
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        String [] arr = str.split(" ");
        double result = getResult(arr);
        System.out.printf("%6f",result);

    }
    public static double getResult(String [] arr){
        Stack<Double> stack = new Stack<>();
        //反向遍历字符串（题目中要求前置表达式）
        for(int i = arr.length-1;i>=0;i--){
            if(arr[i].equals("+") || arr[i].equals("-") ||
                arr[i].equals("*") || arr[i].equals("/")){
                double number1 = stack.pop();
                double number2 = stack.pop();
                switch (arr[i]){
                    case "+":
                        stack.push(number1 + number2);
                        break;
                    case "-":
                        stack.push(number1 - number2);
                        break;
                    case "*":
                        stack.push(number1 * number2);
                        break;
                    case "/":
                        stack.push(number1 / number2);
                        break;
                }
            }else{
                stack.push(Double.parseDouble(arr[i]));
            }
        }
        return stack.pop();
    }
}